1menu "printk and dmesg options" 2 3config PRINTK_TIME 4 bool "Show timing information on printks" 5 depends on PRINTK 6 help 7 Selecting this option causes time stamps of the printk() 8 messages to be added to the output of the syslog() system 9 call and at the console. 10 11 The timestamp is always recorded internally, and exported 12 to /dev/kmsg. This flag just specifies if the timestamp should 13 be included, not that the timestamp is recorded. 14 15 The behavior is also controlled by the kernel command line 16 parameter printk.time=1. See Documentation/admin-guide/kernel-parameters.rst 17 18config CONSOLE_LOGLEVEL_DEFAULT 19 int "Default console loglevel (1-15)" 20 range 1 15 21 default "7" 22 help 23 Default loglevel to determine what will be printed on the console. 24 25 Setting a default here is equivalent to passing in loglevel=<x> in 26 the kernel bootargs. loglevel=<x> continues to override whatever 27 value is specified here as well. 28 29 Note: This does not affect the log level of un-prefixed printk() 30 usage in the kernel. That is controlled by the MESSAGE_LOGLEVEL_DEFAULT 31 option. 32 33config MESSAGE_LOGLEVEL_DEFAULT 34 int "Default message log level (1-7)" 35 range 1 7 36 default "4" 37 help 38 Default log level for printk statements with no specified priority. 39 40 This was hard-coded to KERN_WARNING since at least 2.6.10 but folks 41 that are auditing their logs closely may want to set it to a lower 42 priority. 43 44 Note: This does not affect what message level gets printed on the console 45 by default. To change that, use loglevel=<x> in the kernel bootargs, 46 or pick a different CONSOLE_LOGLEVEL_DEFAULT configuration value. 47 48config BOOT_PRINTK_DELAY 49 bool "Delay each boot printk message by N milliseconds" 50 depends on DEBUG_KERNEL && PRINTK && GENERIC_CALIBRATE_DELAY 51 help 52 This build option allows you to read kernel boot messages 53 by inserting a short delay after each one. The delay is 54 specified in milliseconds on the kernel command line, 55 using "boot_delay=N". 56 57 It is likely that you would also need to use "lpj=M" to preset 58 the "loops per jiffie" value. 59 See a previous boot log for the "lpj" value to use for your 60 system, and then set "lpj=M" before setting "boot_delay=N". 61 NOTE: Using this option may adversely affect SMP systems. 62 I.e., processors other than the first one may not boot up. 63 BOOT_PRINTK_DELAY also may cause LOCKUP_DETECTOR to detect 64 what it believes to be lockup conditions. 65 66config DYNAMIC_DEBUG 67 bool "Enable dynamic printk() support" 68 default n 69 depends on PRINTK 70 depends on DEBUG_FS 71 help 72 73 Compiles debug level messages into the kernel, which would not 74 otherwise be available at runtime. These messages can then be 75 enabled/disabled based on various levels of scope - per source file, 76 function, module, format string, and line number. This mechanism 77 implicitly compiles in all pr_debug() and dev_dbg() calls, which 78 enlarges the kernel text size by about 2%. 79 80 If a source file is compiled with DEBUG flag set, any 81 pr_debug() calls in it are enabled by default, but can be 82 disabled at runtime as below. Note that DEBUG flag is 83 turned on by many CONFIG_*DEBUG* options. 84 85 Usage: 86 87 Dynamic debugging is controlled via the 'dynamic_debug/control' file, 88 which is contained in the 'debugfs' filesystem. Thus, the debugfs 89 filesystem must first be mounted before making use of this feature. 90 We refer the control file as: <debugfs>/dynamic_debug/control. This 91 file contains a list of the debug statements that can be enabled. The 92 format for each line of the file is: 93 94 filename:lineno [module]function flags format 95 96 filename : source file of the debug statement 97 lineno : line number of the debug statement 98 module : module that contains the debug statement 99 function : function that contains the debug statement 100 flags : '=p' means the line is turned 'on' for printing 101 format : the format used for the debug statement 102 103 From a live system: 104 105 nullarbor:~ # cat <debugfs>/dynamic_debug/control 106 # filename:lineno [module]function flags format 107 fs/aio.c:222 [aio]__put_ioctx =_ "__put_ioctx:\040freeing\040%p\012" 108 fs/aio.c:248 [aio]ioctx_alloc =_ "ENOMEM:\040nr_events\040too\040high\012" 109 fs/aio.c:1770 [aio]sys_io_cancel =_ "calling\040cancel\012" 110 111 Example usage: 112 113 // enable the message at line 1603 of file svcsock.c 114 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > 115 <debugfs>/dynamic_debug/control 116 117 // enable all the messages in file svcsock.c 118 nullarbor:~ # echo -n 'file svcsock.c +p' > 119 <debugfs>/dynamic_debug/control 120 121 // enable all the messages in the NFS server module 122 nullarbor:~ # echo -n 'module nfsd +p' > 123 <debugfs>/dynamic_debug/control 124 125 // enable all 12 messages in the function svc_process() 126 nullarbor:~ # echo -n 'func svc_process +p' > 127 <debugfs>/dynamic_debug/control 128 129 // disable all 12 messages in the function svc_process() 130 nullarbor:~ # echo -n 'func svc_process -p' > 131 <debugfs>/dynamic_debug/control 132 133 See Documentation/admin-guide/dynamic-debug-howto.rst for additional 134 information. 135 136endmenu # "printk and dmesg options" 137 138menu "Compile-time checks and compiler options" 139 140config DEBUG_INFO 141 bool "Compile the kernel with debug info" 142 depends on DEBUG_KERNEL && !COMPILE_TEST 143 help 144 If you say Y here the resulting kernel image will include 145 debugging info resulting in a larger kernel image. 146 This adds debug symbols to the kernel and modules (gcc -g), and 147 is needed if you intend to use kernel crashdump or binary object 148 tools like crash, kgdb, LKCD, gdb, etc on the kernel. 149 Say Y here only if you plan to debug the kernel. 150 151 If unsure, say N. 152 153config DEBUG_INFO_REDUCED 154 bool "Reduce debugging information" 155 depends on DEBUG_INFO 156 help 157 If you say Y here gcc is instructed to generate less debugging 158 information for structure types. This means that tools that 159 need full debugging information (like kgdb or systemtap) won't 160 be happy. But if you merely need debugging information to 161 resolve line numbers there is no loss. Advantage is that 162 build directory object sizes shrink dramatically over a full 163 DEBUG_INFO build and compile times are reduced too. 164 Only works with newer gcc versions. 165 166config DEBUG_INFO_SPLIT 167 bool "Produce split debuginfo in .dwo files" 168 depends on DEBUG_INFO 169 help 170 Generate debug info into separate .dwo files. This significantly 171 reduces the build directory size for builds with DEBUG_INFO, 172 because it stores the information only once on disk in .dwo 173 files instead of multiple times in object files and executables. 174 In addition the debug information is also compressed. 175 176 Requires recent gcc (4.7+) and recent gdb/binutils. 177 Any tool that packages or reads debug information would need 178 to know about the .dwo files and include them. 179 Incompatible with older versions of ccache. 180 181config DEBUG_INFO_DWARF4 182 bool "Generate dwarf4 debuginfo" 183 depends on DEBUG_INFO 184 help 185 Generate dwarf4 debug info. This requires recent versions 186 of gcc and gdb. It makes the debug information larger. 187 But it significantly improves the success of resolving 188 variables in gdb on optimized code. 189 190config GDB_SCRIPTS 191 bool "Provide GDB scripts for kernel debugging" 192 depends on DEBUG_INFO 193 help 194 This creates the required links to GDB helper scripts in the 195 build directory. If you load vmlinux into gdb, the helper 196 scripts will be automatically imported by gdb as well, and 197 additional functions are available to analyze a Linux kernel 198 instance. See Documentation/dev-tools/gdb-kernel-debugging.rst 199 for further details. 200 201config ENABLE_WARN_DEPRECATED 202 bool "Enable __deprecated logic" 203 default y 204 help 205 Enable the __deprecated logic in the kernel build. 206 Disable this to suppress the "warning: 'foo' is deprecated 207 (declared at kernel/power/somefile.c:1234)" messages. 208 209config ENABLE_MUST_CHECK 210 bool "Enable __must_check logic" 211 default y 212 help 213 Enable the __must_check logic in the kernel build. Disable this to 214 suppress the "warning: ignoring return value of 'foo', declared with 215 attribute warn_unused_result" messages. 216 217config FRAME_WARN 218 int "Warn for stack frames larger than (needs gcc 4.4)" 219 range 0 8192 220 default 3072 if KASAN_EXTRA 221 default 2048 if GCC_PLUGIN_LATENT_ENTROPY 222 default 1280 if (!64BIT && PARISC) 223 default 1024 if (!64BIT && !PARISC) 224 default 2048 if 64BIT 225 help 226 Tell gcc to warn at build time for stack frames larger than this. 227 Setting this too low will cause a lot of warnings. 228 Setting it to 0 disables the warning. 229 Requires gcc 4.4 230 231config STRIP_ASM_SYMS 232 bool "Strip assembler-generated symbols during link" 233 default n 234 help 235 Strip internal assembler-generated symbols during a link (symbols 236 that look like '.Lxxx') so they don't pollute the output of 237 get_wchan() and suchlike. 238 239config READABLE_ASM 240 bool "Generate readable assembler code" 241 depends on DEBUG_KERNEL 242 help 243 Disable some compiler optimizations that tend to generate human unreadable 244 assembler output. This may make the kernel slightly slower, but it helps 245 to keep kernel developers who have to stare a lot at assembler listings 246 sane. 247 248config UNUSED_SYMBOLS 249 bool "Enable unused/obsolete exported symbols" 250 default y if X86 251 help 252 Unused but exported symbols make the kernel needlessly bigger. For 253 that reason most of these unused exports will soon be removed. This 254 option is provided temporarily to provide a transition period in case 255 some external kernel module needs one of these symbols anyway. If you 256 encounter such a case in your module, consider if you are actually 257 using the right API. (rationale: since nobody in the kernel is using 258 this in a module, there is a pretty good chance it's actually the 259 wrong interface to use). If you really need the symbol, please send a 260 mail to the linux kernel mailing list mentioning the symbol and why 261 you really need it, and what the merge plan to the mainline kernel for 262 your module is. 263 264config PAGE_OWNER 265 bool "Track page owner" 266 depends on DEBUG_KERNEL && STACKTRACE_SUPPORT 267 select DEBUG_FS 268 select STACKTRACE 269 select STACKDEPOT 270 select PAGE_EXTENSION 271 help 272 This keeps track of what call chain is the owner of a page, may 273 help to find bare alloc_page(s) leaks. Even if you include this 274 feature on your build, it is disabled in default. You should pass 275 "page_owner=on" to boot parameter in order to enable it. Eats 276 a fair amount of memory if enabled. See tools/vm/page_owner_sort.c 277 for user-space helper. 278 279 If unsure, say N. 280 281config DEBUG_FS 282 bool "Debug Filesystem" 283 help 284 debugfs is a virtual file system that kernel developers use to put 285 debugging files into. Enable this option to be able to read and 286 write to these files. 287 288 For detailed documentation on the debugfs API, see 289 Documentation/filesystems/. 290 291 If unsure, say N. 292 293config HEADERS_CHECK 294 bool "Run 'make headers_check' when building vmlinux" 295 depends on !UML 296 help 297 This option will extract the user-visible kernel headers whenever 298 building the kernel, and will run basic sanity checks on them to 299 ensure that exported files do not attempt to include files which 300 were not exported, etc. 301 302 If you're making modifications to header files which are 303 relevant for userspace, say 'Y', and check the headers 304 exported to $(INSTALL_HDR_PATH) (usually 'usr/include' in 305 your build tree), to make sure they're suitable. 306 307config DEBUG_SECTION_MISMATCH 308 bool "Enable full Section mismatch analysis" 309 help 310 The section mismatch analysis checks if there are illegal 311 references from one section to another section. 312 During linktime or runtime, some sections are dropped; 313 any use of code/data previously in these sections would 314 most likely result in an oops. 315 In the code, functions and variables are annotated with 316 __init,, etc. (see the full list in include/linux/init.h), 317 which results in the code/data being placed in specific sections. 318 The section mismatch analysis is always performed after a full 319 kernel build, and enabling this option causes the following 320 additional steps to occur: 321 - Add the option -fno-inline-functions-called-once to gcc commands. 322 When inlining a function annotated with __init in a non-init 323 function, we would lose the section information and thus 324 the analysis would not catch the illegal reference. 325 This option tells gcc to inline less (but it does result in 326 a larger kernel). 327 - Run the section mismatch analysis for each module/built-in.a file. 328 When we run the section mismatch analysis on vmlinux.o, we 329 lose valuable information about where the mismatch was 330 introduced. 331 Running the analysis for each module/built-in.a file 332 tells where the mismatch happens much closer to the 333 source. The drawback is that the same mismatch is 334 reported at least twice. 335 - Enable verbose reporting from modpost in order to help resolve 336 the section mismatches that are reported. 337 338config SECTION_MISMATCH_WARN_ONLY 339 bool "Make section mismatch errors non-fatal" 340 default y 341 help 342 If you say N here, the build process will fail if there are any 343 section mismatch, instead of just throwing warnings. 344 345 If unsure, say Y. 346 347# 348# Select this config option from the architecture Kconfig, if it 349# is preferred to always offer frame pointers as a config 350# option on the architecture (regardless of KERNEL_DEBUG): 351# 352config ARCH_WANT_FRAME_POINTERS 353 bool 354 355config FRAME_POINTER 356 bool "Compile the kernel with frame pointers" 357 depends on DEBUG_KERNEL && (M68K || UML || SUPERH) || ARCH_WANT_FRAME_POINTERS 358 default y if (DEBUG_INFO && UML) || ARCH_WANT_FRAME_POINTERS 359 help 360 If you say Y here the resulting kernel image will be slightly 361 larger and slower, but it gives very useful debugging information 362 in case of kernel bugs. (precise oopses/stacktraces/warnings) 363 364config STACK_VALIDATION 365 bool "Compile-time stack metadata validation" 366 depends on HAVE_STACK_VALIDATION 367 default n 368 help 369 Add compile-time checks to validate stack metadata, including frame 370 pointers (if CONFIG_FRAME_POINTER is enabled). This helps ensure 371 that runtime stack traces are more reliable. 372 373 This is also a prerequisite for generation of ORC unwind data, which 374 is needed for CONFIG_UNWINDER_ORC. 375 376 For more information, see 377 tools/objtool/Documentation/stack-validation.txt. 378 379config DEBUG_FORCE_WEAK_PER_CPU 380 bool "Force weak per-cpu definitions" 381 depends on DEBUG_KERNEL 382 help 383 s390 and alpha require percpu variables in modules to be 384 defined weak to work around addressing range issue which 385 puts the following two restrictions on percpu variable 386 definitions. 387 388 1. percpu symbols must be unique whether static or not 389 2. percpu variables can't be defined inside a function 390 391 To ensure that generic code follows the above rules, this 392 option forces all percpu variables to be defined as weak. 393 394endmenu # "Compiler options" 395 396config MAGIC_SYSRQ 397 bool "Magic SysRq key" 398 depends on !UML 399 help 400 If you say Y here, you will have some control over the system even 401 if the system crashes for example during kernel debugging (e.g., you 402 will be able to flush the buffer cache to disk, reboot the system 403 immediately or dump some status information). This is accomplished 404 by pressing various keys while holding SysRq (Alt+PrintScreen). It 405 also works on a serial console (on PC hardware at least), if you 406 send a BREAK and then within 5 seconds a command keypress. The 407 keys are documented in <file:Documentation/admin-guide/sysrq.rst>. 408 Don't say Y unless you really know what this hack does. 409 410config MAGIC_SYSRQ_DEFAULT_ENABLE 411 hex "Enable magic SysRq key functions by default" 412 depends on MAGIC_SYSRQ 413 default 0x1 414 help 415 Specifies which SysRq key functions are enabled by default. 416 This may be set to 1 or 0 to enable or disable them all, or 417 to a bitmask as described in Documentation/admin-guide/sysrq.rst. 418 419config MAGIC_SYSRQ_SERIAL 420 bool "Enable magic SysRq key over serial" 421 depends on MAGIC_SYSRQ 422 default y 423 help 424 Many embedded boards have a disconnected TTL level serial which can 425 generate some garbage that can lead to spurious false sysrq detects. 426 This option allows you to decide whether you want to enable the 427 magic SysRq key. 428 429config DEBUG_KERNEL 430 bool "Kernel debugging" 431 help 432 Say Y here if you are developing drivers or trying to debug and 433 identify kernel problems. 434 435menu "Memory Debugging" 436 437source mm/Kconfig.debug 438 439config DEBUG_OBJECTS 440 bool "Debug object operations" 441 depends on DEBUG_KERNEL 442 help 443 If you say Y here, additional code will be inserted into the 444 kernel to track the life time of various objects and validate 445 the operations on those objects. 446 447config DEBUG_OBJECTS_SELFTEST 448 bool "Debug objects selftest" 449 depends on DEBUG_OBJECTS 450 help 451 This enables the selftest of the object debug code. 452 453config DEBUG_OBJECTS_FREE 454 bool "Debug objects in freed memory" 455 depends on DEBUG_OBJECTS 456 help 457 This enables checks whether a k/v free operation frees an area 458 which contains an object which has not been deactivated 459 properly. This can make kmalloc/kfree-intensive workloads 460 much slower. 461 462config DEBUG_OBJECTS_TIMERS 463 bool "Debug timer objects" 464 depends on DEBUG_OBJECTS 465 help 466 If you say Y here, additional code will be inserted into the 467 timer routines to track the life time of timer objects and 468 validate the timer operations. 469 470config DEBUG_OBJECTS_WORK 471 bool "Debug work objects" 472 depends on DEBUG_OBJECTS 473 help 474 If you say Y here, additional code will be inserted into the 475 work queue routines to track the life time of work objects and 476 validate the work operations. 477 478config DEBUG_OBJECTS_RCU_HEAD 479 bool "Debug RCU callbacks objects" 480 depends on DEBUG_OBJECTS 481 help 482 Enable this to turn on debugging of RCU list heads (call_rcu() usage). 483 484config DEBUG_OBJECTS_PERCPU_COUNTER 485 bool "Debug percpu counter objects" 486 depends on DEBUG_OBJECTS 487 help 488 If you say Y here, additional code will be inserted into the 489 percpu counter routines to track the life time of percpu counter 490 objects and validate the percpu counter operations. 491 492config DEBUG_OBJECTS_ENABLE_DEFAULT 493 int "debug_objects bootup default value (0-1)" 494 range 0 1 495 default "1" 496 depends on DEBUG_OBJECTS 497 help 498 Debug objects boot parameter default value 499 500config DEBUG_SLAB 501 bool "Debug slab memory allocations" 502 depends on DEBUG_KERNEL && SLAB 503 help 504 Say Y here to have the kernel do limited verification on memory 505 allocation as well as poisoning memory on free to catch use of freed 506 memory. This can make kmalloc/kfree-intensive workloads much slower. 507 508config DEBUG_SLAB_LEAK 509 bool "Memory leak debugging" 510 depends on DEBUG_SLAB 511 512config SLUB_DEBUG_ON 513 bool "SLUB debugging on by default" 514 depends on SLUB && SLUB_DEBUG 515 default n 516 help 517 Boot with debugging on by default. SLUB boots by default with 518 the runtime debug capabilities switched off. Enabling this is 519 equivalent to specifying the "slub_debug" parameter on boot. 520 There is no support for more fine grained debug control like 521 possible with slub_debug=xxx. SLUB debugging may be switched 522 off in a kernel built with CONFIG_SLUB_DEBUG_ON by specifying 523 "slub_debug=-". 524 525config SLUB_STATS 526 default n 527 bool "Enable SLUB performance statistics" 528 depends on SLUB && SYSFS 529 help 530 SLUB statistics are useful to debug SLUBs allocation behavior in 531 order find ways to optimize the allocator. This should never be 532 enabled for production use since keeping statistics slows down 533 the allocator by a few percentage points. The slabinfo command 534 supports the determination of the most active slabs to figure 535 out which slabs are relevant to a particular load. 536 Try running: slabinfo -DA 537 538config HAVE_DEBUG_KMEMLEAK 539 bool 540 541config DEBUG_KMEMLEAK 542 bool "Kernel memory leak detector" 543 depends on DEBUG_KERNEL && HAVE_DEBUG_KMEMLEAK 544 select DEBUG_FS 545 select STACKTRACE if STACKTRACE_SUPPORT 546 select KALLSYMS 547 select CRC32 548 help 549 Say Y here if you want to enable the memory leak 550 detector. The memory allocation/freeing is traced in a way 551 similar to the Boehm's conservative garbage collector, the 552 difference being that the orphan objects are not freed but 553 only shown in /sys/kernel/debug/kmemleak. Enabling this 554 feature will introduce an overhead to memory 555 allocations. See Documentation/dev-tools/kmemleak.rst for more 556 details. 557 558 Enabling DEBUG_SLAB or SLUB_DEBUG may increase the chances 559 of finding leaks due to the slab objects poisoning. 560 561 In order to access the kmemleak file, debugfs needs to be 562 mounted (usually at /sys/kernel/debug). 563 564config DEBUG_KMEMLEAK_EARLY_LOG_SIZE 565 int "Maximum kmemleak early log entries" 566 depends on DEBUG_KMEMLEAK 567 range 200 40000 568 default 400 569 help 570 Kmemleak must track all the memory allocations to avoid 571 reporting false positives. Since memory may be allocated or 572 freed before kmemleak is initialised, an early log buffer is 573 used to store these actions. If kmemleak reports "early log 574 buffer exceeded", please increase this value. 575 576config DEBUG_KMEMLEAK_TEST 577 tristate "Simple test for the kernel memory leak detector" 578 depends on DEBUG_KMEMLEAK && m 579 help 580 This option enables a module that explicitly leaks memory. 581 582 If unsure, say N. 583 584config DEBUG_KMEMLEAK_DEFAULT_OFF 585 bool "Default kmemleak to off" 586 depends on DEBUG_KMEMLEAK 587 help 588 Say Y here to disable kmemleak by default. It can then be enabled 589 on the command line via kmemleak=on. 590 591config DEBUG_STACK_USAGE 592 bool "Stack utilization instrumentation" 593 depends on DEBUG_KERNEL && !IA64 594 help 595 Enables the display of the minimum amount of free stack which each 596 task has ever had available in the sysrq-T and sysrq-P debug output. 597 598 This option will slow down process creation somewhat. 599 600config DEBUG_VM 601 bool "Debug VM" 602 depends on DEBUG_KERNEL 603 help 604 Enable this to turn on extended checks in the virtual-memory system 605 that may impact performance. 606 607 If unsure, say N. 608 609config DEBUG_VM_VMACACHE 610 bool "Debug VMA caching" 611 depends on DEBUG_VM 612 help 613 Enable this to turn on VMA caching debug information. Doing so 614 can cause significant overhead, so only enable it in non-production 615 environments. 616 617 If unsure, say N. 618 619config DEBUG_VM_RB 620 bool "Debug VM red-black trees" 621 depends on DEBUG_VM 622 help 623 Enable VM red-black tree debugging information and extra validations. 624 625 If unsure, say N. 626 627config DEBUG_VM_PGFLAGS 628 bool "Debug page-flags operations" 629 depends on DEBUG_VM 630 help 631 Enables extra validation on page flags operations. 632 633 If unsure, say N. 634 635config ARCH_HAS_DEBUG_VIRTUAL 636 bool 637 638config DEBUG_VIRTUAL 639 bool "Debug VM translations" 640 depends on DEBUG_KERNEL && ARCH_HAS_DEBUG_VIRTUAL 641 help 642 Enable some costly sanity checks in virtual to page code. This can 643 catch mistakes with virt_to_page() and friends. 644 645 If unsure, say N. 646 647config DEBUG_NOMMU_REGIONS 648 bool "Debug the global anon/private NOMMU mapping region tree" 649 depends on DEBUG_KERNEL && !MMU 650 help 651 This option causes the global tree of anonymous and private mapping 652 regions to be regularly checked for invalid topology. 653 654config DEBUG_MEMORY_INIT 655 bool "Debug memory initialisation" if EXPERT 656 default !EXPERT 657 help 658 Enable this for additional checks during memory initialisation. 659 The sanity checks verify aspects of the VM such as the memory model 660 and other information provided by the architecture. Verbose 661 information will be printed at KERN_DEBUG loglevel depending 662 on the mminit_loglevel= command-line option. 663 664 If unsure, say Y 665 666config MEMORY_NOTIFIER_ERROR_INJECT 667 tristate "Memory hotplug notifier error injection module" 668 depends on MEMORY_HOTPLUG_SPARSE && NOTIFIER_ERROR_INJECTION 669 help 670 This option provides the ability to inject artificial errors to 671 memory hotplug notifier chain callbacks. It is controlled through 672 debugfs interface under /sys/kernel/debug/notifier-error-inject/memory 673 674 If the notifier call chain should be failed with some events 675 notified, write the error code to "actions/<notifier event>/error". 676 677 Example: Inject memory hotplug offline error (-12 == -ENOMEM) 678 679 # cd /sys/kernel/debug/notifier-error-inject/memory 680 # echo -12 > actions/MEM_GOING_OFFLINE/error 681 # echo offline > /sys/devices/system/memory/memoryXXX/state 682 bash: echo: write error: Cannot allocate memory 683 684 To compile this code as a module, choose M here: the module will 685 be called memory-notifier-error-inject. 686 687 If unsure, say N. 688 689config DEBUG_PER_CPU_MAPS 690 bool "Debug access to per_cpu maps" 691 depends on DEBUG_KERNEL 692 depends on SMP 693 help 694 Say Y to verify that the per_cpu map being accessed has 695 been set up. This adds a fair amount of code to kernel memory 696 and decreases performance. 697 698 Say N if unsure. 699 700config DEBUG_HIGHMEM 701 bool "Highmem debugging" 702 depends on DEBUG_KERNEL && HIGHMEM 703 help 704 This option enables additional error checking for high memory 705 systems. Disable for production systems. 706 707config HAVE_DEBUG_STACKOVERFLOW 708 bool 709 710config DEBUG_STACKOVERFLOW 711 bool "Check for stack overflows" 712 depends on DEBUG_KERNEL && HAVE_DEBUG_STACKOVERFLOW 713 ---help--- 714 Say Y here if you want to check for overflows of kernel, IRQ 715 and exception stacks (if your architecture uses them). This 716 option will show detailed messages if free stack space drops 717 below a certain limit. 718 719 These kinds of bugs usually occur when call-chains in the 720 kernel get too deep, especially when interrupts are 721 involved. 722 723 Use this in cases where you see apparently random memory 724 corruption, especially if it appears in 'struct thread_info' 725 726 If in doubt, say "N". 727 728source "lib/Kconfig.kasan" 729 730endmenu # "Memory Debugging" 731 732config ARCH_HAS_KCOV 733 bool 734 help 735 KCOV does not have any arch-specific code, but currently it is enabled 736 only for x86_64. KCOV requires testing on other archs, and most likely 737 disabling of instrumentation for some early boot code. 738 739config KCOV 740 bool "Code coverage for fuzzing" 741 depends on ARCH_HAS_KCOV 742 select DEBUG_FS 743 select GCC_PLUGINS if !COMPILE_TEST 744 select GCC_PLUGIN_SANCOV if !COMPILE_TEST 745 help 746 KCOV exposes kernel code coverage information in a form suitable 747 for coverage-guided fuzzing (randomized testing). 748 749 If RANDOMIZE_BASE is enabled, PC values will not be stable across 750 different machines and across reboots. If you need stable PC values, 751 disable RANDOMIZE_BASE. 752 753 For more details, see Documentation/dev-tools/kcov.rst. 754 755config KCOV_ENABLE_COMPARISONS 756 bool "Enable comparison operands collection by KCOV" 757 depends on KCOV 758 default n 759 help 760 KCOV also exposes operands of every comparison in the instrumented 761 code along with operand sizes and PCs of the comparison instructions. 762 These operands can be used by fuzzing engines to improve the quality 763 of fuzzing coverage. 764 765config KCOV_INSTRUMENT_ALL 766 bool "Instrument all code by default" 767 depends on KCOV 768 default y if KCOV 769 help 770 If you are doing generic system call fuzzing (like e.g. syzkaller), 771 then you will want to instrument the whole kernel and you should 772 say y here. If you are doing more targeted fuzzing (like e.g. 773 filesystem fuzzing with AFL) then you will want to enable coverage 774 for more specific subsets of files, and should say n here. 775 776config DEBUG_SHIRQ 777 bool "Debug shared IRQ handlers" 778 depends on DEBUG_KERNEL 779 help 780 Enable this to generate a spurious interrupt as soon as a shared 781 interrupt handler is registered, and just before one is deregistered. 782 Drivers ought to be able to handle interrupts coming in at those 783 points; some don't and need to be caught. 784 785menu "Debug Lockups and Hangs" 786 787config LOCKUP_DETECTOR 788 bool 789 790config SOFTLOCKUP_DETECTOR 791 bool "Detect Soft Lockups" 792 depends on DEBUG_KERNEL && !S390 793 select LOCKUP_DETECTOR 794 help 795 Say Y here to enable the kernel to act as a watchdog to detect 796 soft lockups. 797 798 Softlockups are bugs that cause the kernel to loop in kernel 799 mode for more than 20 seconds, without giving other tasks a 800 chance to run. The current stack trace is displayed upon 801 detection and the system will stay locked up. 802 803config BOOTPARAM_SOFTLOCKUP_PANIC 804 bool "Panic (Reboot) On Soft Lockups" 805 depends on SOFTLOCKUP_DETECTOR 806 help 807 Say Y here to enable the kernel to panic on "soft lockups", 808 which are bugs that cause the kernel to loop in kernel 809 mode for more than 20 seconds (configurable using the watchdog_thresh 810 sysctl), without giving other tasks a chance to run. 811 812 The panic can be used in combination with panic_timeout, 813 to cause the system to reboot automatically after a 814 lockup has been detected. This feature is useful for 815 high-availability systems that have uptime guarantees and 816 where a lockup must be resolved ASAP. 817 818 Say N if unsure. 819 820config BOOTPARAM_SOFTLOCKUP_PANIC_VALUE 821 int 822 depends on SOFTLOCKUP_DETECTOR 823 range 0 1 824 default 0 if !BOOTPARAM_SOFTLOCKUP_PANIC 825 default 1 if BOOTPARAM_SOFTLOCKUP_PANIC 826 827config HARDLOCKUP_DETECTOR_PERF 828 bool 829 select SOFTLOCKUP_DETECTOR 830 831# 832# Enables a timestamp based low pass filter to compensate for perf based 833# hard lockup detection which runs too fast due to turbo modes. 834# 835config HARDLOCKUP_CHECK_TIMESTAMP 836 bool 837 838# 839# arch/ can define HAVE_HARDLOCKUP_DETECTOR_ARCH to provide their own hard 840# lockup detector rather than the perf based detector. 841# 842config HARDLOCKUP_DETECTOR 843 bool "Detect Hard Lockups" 844 depends on DEBUG_KERNEL && !S390 845 depends on HAVE_HARDLOCKUP_DETECTOR_PERF || HAVE_HARDLOCKUP_DETECTOR_ARCH 846 select LOCKUP_DETECTOR 847 select HARDLOCKUP_DETECTOR_PERF if HAVE_HARDLOCKUP_DETECTOR_PERF 848 select HARDLOCKUP_DETECTOR_ARCH if HAVE_HARDLOCKUP_DETECTOR_ARCH 849 help 850 Say Y here to enable the kernel to act as a watchdog to detect 851 hard lockups. 852 853 Hardlockups are bugs that cause the CPU to loop in kernel mode 854 for more than 10 seconds, without letting other interrupts have a 855 chance to run. The current stack trace is displayed upon detection 856 and the system will stay locked up. 857 858config BOOTPARAM_HARDLOCKUP_PANIC 859 bool "Panic (Reboot) On Hard Lockups" 860 depends on HARDLOCKUP_DETECTOR 861 help 862 Say Y here to enable the kernel to panic on "hard lockups", 863 which are bugs that cause the kernel to loop in kernel 864 mode with interrupts disabled for more than 10 seconds (configurable 865 using the watchdog_thresh sysctl). 866 867 Say N if unsure. 868 869config BOOTPARAM_HARDLOCKUP_PANIC_VALUE 870 int 871 depends on HARDLOCKUP_DETECTOR 872 range 0 1 873 default 0 if !BOOTPARAM_HARDLOCKUP_PANIC 874 default 1 if BOOTPARAM_HARDLOCKUP_PANIC 875 876config DETECT_HUNG_TASK 877 bool "Detect Hung Tasks" 878 depends on DEBUG_KERNEL 879 default SOFTLOCKUP_DETECTOR 880 help 881 Say Y here to enable the kernel to detect "hung tasks", 882 which are bugs that cause the task to be stuck in 883 uninterruptible "D" state indefinitely. 884 885 When a hung task is detected, the kernel will print the 886 current stack trace (which you should report), but the 887 task will stay in uninterruptible state. If lockdep is 888 enabled then all held locks will also be reported. This 889 feature has negligible overhead. 890 891config DEFAULT_HUNG_TASK_TIMEOUT 892 int "Default timeout for hung task detection (in seconds)" 893 depends on DETECT_HUNG_TASK 894 default 120 895 help 896 This option controls the default timeout (in seconds) used 897 to determine when a task has become non-responsive and should 898 be considered hung. 899 900 It can be adjusted at runtime via the kernel.hung_task_timeout_secs 901 sysctl or by writing a value to 902 /proc/sys/kernel/hung_task_timeout_secs. 903 904 A timeout of 0 disables the check. The default is two minutes. 905 Keeping the default should be fine in most cases. 906 907config BOOTPARAM_HUNG_TASK_PANIC 908 bool "Panic (Reboot) On Hung Tasks" 909 depends on DETECT_HUNG_TASK 910 help 911 Say Y here to enable the kernel to panic on "hung tasks", 912 which are bugs that cause the kernel to leave a task stuck 913 in uninterruptible "D" state. 914 915 The panic can be used in combination with panic_timeout, 916 to cause the system to reboot automatically after a 917 hung task has been detected. This feature is useful for 918 high-availability systems that have uptime guarantees and 919 where a hung tasks must be resolved ASAP. 920 921 Say N if unsure. 922 923config BOOTPARAM_HUNG_TASK_PANIC_VALUE 924 int 925 depends on DETECT_HUNG_TASK 926 range 0 1 927 default 0 if !BOOTPARAM_HUNG_TASK_PANIC 928 default 1 if BOOTPARAM_HUNG_TASK_PANIC 929 930config WQ_WATCHDOG 931 bool "Detect Workqueue Stalls" 932 depends on DEBUG_KERNEL 933 help 934 Say Y here to enable stall detection on workqueues. If a 935 worker pool doesn't make forward progress on a pending work 936 item for over a given amount of time, 30s by default, a 937 warning message is printed along with dump of workqueue 938 state. This can be configured through kernel parameter 939 "workqueue.watchdog_thresh" and its sysfs counterpart. 940 941endmenu # "Debug lockups and hangs" 942 943config PANIC_ON_OOPS 944 bool "Panic on Oops" 945 help 946 Say Y here to enable the kernel to panic when it oopses. This 947 has the same effect as setting oops=panic on the kernel command 948 line. 949 950 This feature is useful to ensure that the kernel does not do 951 anything erroneous after an oops which could result in data 952 corruption or other issues. 953 954 Say N if unsure. 955 956config PANIC_ON_OOPS_VALUE 957 int 958 range 0 1 959 default 0 if !PANIC_ON_OOPS 960 default 1 if PANIC_ON_OOPS 961 962config PANIC_TIMEOUT 963 int "panic timeout" 964 default 0 965 help 966 Set the timeout value (in seconds) until a reboot occurs when the 967 the kernel panics. If n = 0, then we wait forever. A timeout 968 value n > 0 will wait n seconds before rebooting, while a timeout 969 value n < 0 will reboot immediately. 970 971config SCHED_DEBUG 972 bool "Collect scheduler debugging info" 973 depends on DEBUG_KERNEL && PROC_FS 974 default y 975 help 976 If you say Y here, the /proc/sched_debug file will be provided 977 that can help debug the scheduler. The runtime overhead of this 978 option is minimal. 979 980config SCHED_INFO 981 bool 982 default n 983 984config SCHEDSTATS 985 bool "Collect scheduler statistics" 986 depends on DEBUG_KERNEL && PROC_FS 987 select SCHED_INFO 988 help 989 If you say Y here, additional code will be inserted into the 990 scheduler and related routines to collect statistics about 991 scheduler behavior and provide them in /proc/schedstat. These 992 stats may be useful for both tuning and debugging the scheduler 993 If you aren't debugging the scheduler or trying to tune a specific 994 application, you can say N to avoid the very slight overhead 995 this adds. 996 997config SCHED_STACK_END_CHECK 998 bool "Detect stack corruption on calls to schedule()" 999 depends on DEBUG_KERNEL 1000 default n
1001 help 1002 This option checks for a stack overrun on calls to schedule(). 1003 If the stack end location is found to be over written always panic as 1004 the content of the corrupted region can no longer be trusted. 1005 This is to ensure no erroneous behaviour occurs which could result in 1006 data corruption or a sporadic crash at a later stage once the region 1007 is examined. The runtime overhead introduced is minimal. 1008 1009config DEBUG_TIMEKEEPING 1010 bool "Enable extra timekeeping sanity checking" 1011 help 1012 This option will enable additional timekeeping sanity checks 1013 which may be helpful when diagnosing issues where timekeeping 1014 problems are suspected. 1015 1016 This may include checks in the timekeeping hotpaths, so this 1017 option may have a (very small) performance impact to some 1018 workloads. 1019 1020 If unsure, say N. 1021 1022config DEBUG_PREEMPT 1023 bool "Debug preemptible kernel" 1024 depends on DEBUG_KERNEL && PREEMPT && TRACE_IRQFLAGS_SUPPORT 1025 default y 1026 help 1027 If you say Y here then the kernel will use a debug variant of the 1028 commonly used smp_processor_id() function and will print warnings 1029 if kernel code uses it in a preemption-unsafe way. Also, the kernel 1030 will detect preemption count underflows. 1031 1032menu "Lock Debugging (spinlocks, mutexes, etc...)" 1033 1034config LOCK_DEBUGGING_SUPPORT 1035 bool 1036 depends on TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1037 default y 1038 1039config PROVE_LOCKING 1040 bool "Lock debugging: prove locking correctness" 1041 depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT 1042 select LOCKDEP 1043 select DEBUG_SPINLOCK 1044 select DEBUG_MUTEXES 1045 select DEBUG_RT_MUTEXES if RT_MUTEXES 1046 select DEBUG_RWSEMS if RWSEM_SPIN_ON_OWNER 1047 select DEBUG_WW_MUTEX_SLOWPATH 1048 select DEBUG_LOCK_ALLOC 1049 select TRACE_IRQFLAGS 1050 default n 1051 help 1052 This feature enables the kernel to prove that all locking 1053 that occurs in the kernel runtime is mathematically 1054 correct: that under no circumstance could an arbitrary (and 1055 not yet triggered) combination of observed locking 1056 sequences (on an arbitrary number of CPUs, running an 1057 arbitrary number of tasks and interrupt contexts) cause a 1058 deadlock. 1059 1060 In short, this feature enables the kernel to report locking 1061 related deadlocks before they actually occur. 1062 1063 The proof does not depend on how hard and complex a 1064 deadlock scenario would be to trigger: how many 1065 participant CPUs, tasks and irq-contexts would be needed 1066 for it to trigger. The proof also does not depend on 1067 timing: if a race and a resulting deadlock is possible 1068 theoretically (no matter how unlikely the race scenario 1069 is), it will be proven so and will immediately be 1070 reported by the kernel (once the event is observed that 1071 makes the deadlock theoretically possible). 1072 1073 If a deadlock is impossible (i.e. the locking rules, as 1074 observed by the kernel, are mathematically correct), the 1075 kernel reports nothing. 1076 1077 NOTE: this feature can also be enabled for rwlocks, mutexes 1078 and rwsems - in which case all dependencies between these 1079 different locking variants are observed and mapped too, and 1080 the proof of observed correctness is also maintained for an 1081 arbitrary combination of these separate locking variants. 1082 1083 For more details, see Documentation/locking/lockdep-design.txt. 1084 1085config LOCK_STAT 1086 bool "Lock usage statistics" 1087 depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT 1088 select LOCKDEP 1089 select DEBUG_SPINLOCK 1090 select DEBUG_MUTEXES 1091 select DEBUG_RT_MUTEXES if RT_MUTEXES 1092 select DEBUG_LOCK_ALLOC 1093 default n 1094 help 1095 This feature enables tracking lock contention points 1096 1097 For more details, see Documentation/locking/lockstat.txt 1098 1099 This also enables lock events required by "perf lock", 1100 subcommand of perf. 1101 If you want to use "perf lock", you also need to turn on 1102 CONFIG_EVENT_TRACING. 1103 1104 CONFIG_LOCK_STAT defines "contended" and "acquired" lock events. 1105 (CONFIG_LOCKDEP defines "acquire" and "release" events.) 1106 1107config DEBUG_RT_MUTEXES 1108 bool "RT Mutex debugging, deadlock detection" 1109 depends on DEBUG_KERNEL && RT_MUTEXES 1110 help 1111 This allows rt mutex semantics violations and rt mutex related 1112 deadlocks (lockups) to be detected and reported automatically. 1113 1114config DEBUG_SPINLOCK 1115 bool "Spinlock and rw-lock debugging: basic checks" 1116 depends on DEBUG_KERNEL 1117 select UNINLINE_SPIN_UNLOCK 1118 help 1119 Say Y here and build SMP to catch missing spinlock initialization 1120 and certain other kinds of spinlock errors commonly made. This is 1121 best used in conjunction with the NMI watchdog so that spinlock 1122 deadlocks are also debuggable. 1123 1124config DEBUG_MUTEXES 1125 bool "Mutex debugging: basic checks" 1126 depends on DEBUG_KERNEL 1127 help 1128 This feature allows mutex semantics violations to be detected and 1129 reported. 1130 1131config DEBUG_WW_MUTEX_SLOWPATH 1132 bool "Wait/wound mutex debugging: Slowpath testing" 1133 depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT 1134 select DEBUG_LOCK_ALLOC 1135 select DEBUG_SPINLOCK 1136 select DEBUG_MUTEXES 1137 help 1138 This feature enables slowpath testing for w/w mutex users by 1139 injecting additional -EDEADLK wound/backoff cases. Together with 1140 the full mutex checks enabled with (CONFIG_PROVE_LOCKING) this 1141 will test all possible w/w mutex interface abuse with the 1142 exception of simply not acquiring all the required locks. 1143 Note that this feature can introduce significant overhead, so 1144 it really should not be enabled in a production or distro kernel, 1145 even a debug kernel. If you are a driver writer, enable it. If 1146 you are a distro, do not. 1147 1148config DEBUG_RWSEMS 1149 bool "RW Semaphore debugging: basic checks" 1150 depends on DEBUG_KERNEL && RWSEM_SPIN_ON_OWNER 1151 help 1152 This debugging feature allows mismatched rw semaphore locks and unlocks 1153 to be detected and reported. 1154 1155config DEBUG_LOCK_ALLOC 1156 bool "Lock debugging: detect incorrect freeing of live locks" 1157 depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT 1158 select DEBUG_SPINLOCK 1159 select DEBUG_MUTEXES 1160 select DEBUG_RT_MUTEXES if RT_MUTEXES 1161 select LOCKDEP 1162 help 1163 This feature will check whether any held lock (spinlock, rwlock, 1164 mutex or rwsem) is incorrectly freed by the kernel, via any of the 1165 memory-freeing routines (kfree(), kmem_cache_free(), free_pages(), 1166 vfree(), etc.), whether a live lock is incorrectly reinitialized via 1167 spin_lock_init()/mutex_init()/etc., or whether there is any lock 1168 held during task exit. 1169 1170config LOCKDEP 1171 bool 1172 depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT 1173 select STACKTRACE 1174 select FRAME_POINTER if !MIPS && !PPC && !ARM_UNWIND && !S390 && !MICROBLAZE && !ARC && !X86 1175 select KALLSYMS 1176 select KALLSYMS_ALL 1177 1178config LOCKDEP_SMALL 1179 bool 1180 1181config DEBUG_LOCKDEP 1182 bool "Lock dependency engine debugging" 1183 depends on DEBUG_KERNEL && LOCKDEP 1184 help 1185 If you say Y here, the lock dependency engine will do 1186 additional runtime checks to debug itself, at the price 1187 of more runtime overhead. 1188 1189config DEBUG_ATOMIC_SLEEP 1190 bool "Sleep inside atomic section checking" 1191 select PREEMPT_COUNT 1192 depends on DEBUG_KERNEL 1193 help 1194 If you say Y here, various routines which may sleep will become very 1195 noisy if they are called inside atomic sections: when a spinlock is 1196 held, inside an rcu read side critical section, inside preempt disabled 1197 sections, inside an interrupt, etc... 1198 1199config DEBUG_LOCKING_API_SELFTESTS 1200 bool "Locking API boot-time self-tests" 1201 depends on DEBUG_KERNEL 1202 help 1203 Say Y here if you want the kernel to run a short self-test during 1204 bootup. The self-test checks whether common types of locking bugs 1205 are detected by debugging mechanisms or not. (if you disable 1206 lock debugging then those bugs wont be detected of course.) 1207 The following locking APIs are covered: spinlocks, rwlocks, 1208 mutexes and rwsems. 1209 1210config LOCK_TORTURE_TEST 1211 tristate "torture tests for locking" 1212 depends on DEBUG_KERNEL 1213 select TORTURE_TEST 1214 default n 1215 help 1216 This option provides a kernel module that runs torture tests 1217 on kernel locking primitives. The kernel module may be built 1218 after the fact on the running kernel to be tested, if desired. 1219 1220 Say Y here if you want kernel locking-primitive torture tests 1221 to be built into the kernel. 1222 Say M if you want these torture tests to build as a module. 1223 Say N if you are unsure. 1224 1225config WW_MUTEX_SELFTEST 1226 tristate "Wait/wound mutex selftests" 1227 help 1228 This option provides a kernel module that runs tests on the 1229 on the struct ww_mutex locking API. 1230 1231 It is recommended to enable DEBUG_WW_MUTEX_SLOWPATH in conjunction 1232 with this test harness. 1233 1234 Say M if you want these self tests to build as a module. 1235 Say N if you are unsure. 1236 1237endmenu # lock debugging 1238 1239config TRACE_IRQFLAGS 1240 bool 1241 help 1242 Enables hooks to interrupt enabling and disabling for 1243 either tracing or lock debugging. 1244 1245config STACKTRACE 1246 bool "Stack backtrace support" 1247 depends on STACKTRACE_SUPPORT 1248 help 1249 This option causes the kernel to create a /proc/pid/stack for 1250 every process, showing its current stack trace. 1251 It is also used by various kernel debugging features that require 1252 stack trace generation. 1253 1254config WARN_ALL_UNSEEDED_RANDOM 1255 bool "Warn for all uses of unseeded randomness" 1256 default n 1257 help 1258 Some parts of the kernel contain bugs relating to their use of 1259 cryptographically secure random numbers before it's actually possible 1260 to generate those numbers securely. This setting ensures that these 1261 flaws don't go unnoticed, by enabling a message, should this ever 1262 occur. This will allow people with obscure setups to know when things 1263 are going wrong, so that they might contact developers about fixing 1264 it. 1265 1266 Unfortunately, on some models of some architectures getting 1267 a fully seeded CRNG is extremely difficult, and so this can 1268 result in dmesg getting spammed for a surprisingly long 1269 time. This is really bad from a security perspective, and 1270 so architecture maintainers really need to do what they can 1271 to get the CRNG seeded sooner after the system is booted. 1272 However, since users can not do anything actionble to 1273 address this, by default the kernel will issue only a single 1274 warning for the first use of unseeded randomness. 1275 1276 Say Y here if you want to receive warnings for all uses of 1277 unseeded randomness. This will be of use primarily for 1278 those developers interersted in improving the security of 1279 Linux kernels running on their architecture (or 1280 subarchitecture). 1281 1282config DEBUG_KOBJECT 1283 bool "kobject debugging" 1284 depends on DEBUG_KERNEL 1285 help 1286 If you say Y here, some extra kobject debugging messages will be sent 1287 to the syslog. 1288 1289config DEBUG_KOBJECT_RELEASE 1290 bool "kobject release debugging" 1291 depends on DEBUG_OBJECTS_TIMERS 1292 help 1293 kobjects are reference counted objects. This means that their 1294 last reference count put is not predictable, and the kobject can 1295 live on past the point at which a driver decides to drop it's 1296 initial reference to the kobject gained on allocation. An 1297 example of this would be a struct device which has just been 1298 unregistered. 1299 1300 However, some buggy drivers assume that after such an operation, 1301 the memory backing the kobject can be immediately freed. This 1302 goes completely against the principles of a refcounted object. 1303 1304 If you say Y here, the kernel will delay the release of kobjects 1305 on the last reference count to improve the visibility of this 1306 kind of kobject release bug. 1307 1308config HAVE_DEBUG_BUGVERBOSE 1309 bool 1310 1311config DEBUG_BUGVERBOSE 1312 bool "Verbose BUG() reporting (adds 70K)" if DEBUG_KERNEL && EXPERT 1313 depends on BUG && (GENERIC_BUG || HAVE_DEBUG_BUGVERBOSE) 1314 default y 1315 help 1316 Say Y here to make BUG() panics output the file name and line number 1317 of the BUG call as well as the EIP and oops trace. This aids 1318 debugging but costs about 70-100K of memory. 1319 1320config DEBUG_LIST 1321 bool "Debug linked list manipulation" 1322 depends on DEBUG_KERNEL || BUG_ON_DATA_CORRUPTION 1323 help 1324 Enable this to turn on extended checks in the linked-list 1325 walking routines. 1326 1327 If unsure, say N. 1328 1329config DEBUG_PI_LIST 1330 bool "Debug priority linked list manipulation" 1331 depends on DEBUG_KERNEL 1332 help 1333 Enable this to turn on extended checks in the priority-ordered 1334 linked-list (plist) walking routines. This checks the entire 1335 list multiple times during each manipulation. 1336 1337 If unsure, say N. 1338 1339config DEBUG_SG 1340 bool "Debug SG table operations" 1341 depends on DEBUG_KERNEL 1342 help 1343 Enable this to turn on checks on scatter-gather tables. This can 1344 help find problems with drivers that do not properly initialize 1345 their sg tables. 1346 1347 If unsure, say N. 1348 1349config DEBUG_NOTIFIERS 1350 bool "Debug notifier call chains" 1351 depends on DEBUG_KERNEL 1352 help 1353 Enable this to turn on sanity checking for notifier call chains. 1354 This is most useful for kernel developers to make sure that 1355 modules properly unregister themselves from notifier chains. 1356 This is a relatively cheap check but if you care about maximum 1357 performance, say N. 1358 1359config DEBUG_CREDENTIALS 1360 bool "Debug credential management" 1361 depends on DEBUG_KERNEL 1362 help 1363 Enable this to turn on some debug checking for credential 1364 management. The additional code keeps track of the number of 1365 pointers from task_structs to any given cred struct, and checks to 1366 see that this number never exceeds the usage count of the cred 1367 struct. 1368 1369 Furthermore, if SELinux is enabled, this also checks that the 1370 security pointer in the cred struct is never seen to be invalid. 1371 1372 If unsure, say N. 1373 1374source "kernel/rcu/Kconfig.debug" 1375 1376config DEBUG_WQ_FORCE_RR_CPU 1377 bool "Force round-robin CPU selection for unbound work items" 1378 depends on DEBUG_KERNEL 1379 default n 1380 help 1381 Workqueue used to implicitly guarantee that work items queued 1382 without explicit CPU specified are put on the local CPU. This 1383 guarantee is no longer true and while local CPU is still 1384 preferred work items may be put on foreign CPUs. Kernel 1385 parameter "workqueue.debug_force_rr_cpu" is added to force 1386 round-robin CPU selection to flush out usages which depend on the 1387 now broken guarantee. This config option enables the debug 1388 feature by default. When enabled, memory and cache locality will 1389 be impacted. 1390 1391config DEBUG_BLOCK_EXT_DEVT 1392 bool "Force extended block device numbers and spread them" 1393 depends on DEBUG_KERNEL 1394 depends on BLOCK 1395 default n 1396 help 1397 BIG FAT WARNING: ENABLING THIS OPTION MIGHT BREAK BOOTING ON 1398 SOME DISTRIBUTIONS. DO NOT ENABLE THIS UNLESS YOU KNOW WHAT 1399 YOU ARE DOING. Distros, please enable this and fix whatever 1400 is broken. 1401 1402 Conventionally, block device numbers are allocated from 1403 predetermined contiguous area. However, extended block area 1404 may introduce non-contiguous block device numbers. This 1405 option forces most block device numbers to be allocated from 1406 the extended space and spreads them to discover kernel or 1407 userland code paths which assume predetermined contiguous 1408 device number allocation. 1409 1410 Note that turning on this debug option shuffles all the 1411 device numbers for all IDE and SCSI devices including libata 1412 ones, so root partition specified using device number 1413 directly (via rdev or root=MAJ:MIN) won't work anymore. 1414 Textual device names (root=/dev/sdXn) will continue to work. 1415 1416 Say N if you are unsure. 1417 1418config CPU_HOTPLUG_STATE_CONTROL 1419 bool "Enable CPU hotplug state control" 1420 depends on DEBUG_KERNEL 1421 depends on HOTPLUG_CPU 1422 default n 1423 help 1424 Allows to write steps between "offline" and "online" to the CPUs 1425 sysfs target file so states can be stepped granular. This is a debug 1426 option for now as the hotplug machinery cannot be stopped and 1427 restarted at arbitrary points yet. 1428 1429 Say N if your are unsure. 1430 1431config NOTIFIER_ERROR_INJECTION 1432 tristate "Notifier error injection" 1433 depends on DEBUG_KERNEL 1434 select DEBUG_FS 1435 help 1436 This option provides the ability to inject artificial errors to 1437 specified notifier chain callbacks. It is useful to test the error 1438 handling of notifier call chain failures. 1439 1440 Say N if unsure. 1441 1442config PM_NOTIFIER_ERROR_INJECT 1443 tristate "PM notifier error injection module" 1444 depends on PM && NOTIFIER_ERROR_INJECTION 1445 default m if PM_DEBUG 1446 help 1447 This option provides the ability to inject artificial errors to 1448 PM notifier chain callbacks. It is controlled through debugfs 1449 interface /sys/kernel/debug/notifier-error-inject/pm 1450 1451 If the notifier call chain should be failed with some events 1452 notified, write the error code to "actions/<notifier event>/error". 1453 1454 Example: Inject PM suspend error (-12 = -ENOMEM) 1455 1456 # cd /sys/kernel/debug/notifier-error-inject/pm/ 1457 # echo -12 > actions/PM_SUSPEND_PREPARE/error 1458 # echo mem > /sys/power/state 1459 bash: echo: write error: Cannot allocate memory 1460 1461 To compile this code as a module, choose M here: the module will 1462 be called pm-notifier-error-inject. 1463 1464 If unsure, say N. 1465 1466config OF_RECONFIG_NOTIFIER_ERROR_INJECT 1467 tristate "OF reconfig notifier error injection module" 1468 depends on OF_DYNAMIC && NOTIFIER_ERROR_INJECTION 1469 help 1470 This option provides the ability to inject artificial errors to 1471 OF reconfig notifier chain callbacks. It is controlled 1472 through debugfs interface under 1473 /sys/kernel/debug/notifier-error-inject/OF-reconfig/ 1474 1475 If the notifier call chain should be failed with some events 1476 notified, write the error code to "actions/<notifier event>/error". 1477 1478 To compile this code as a module, choose M here: the module will 1479 be called of-reconfig-notifier-error-inject. 1480 1481 If unsure, say N. 1482 1483config NETDEV_NOTIFIER_ERROR_INJECT 1484 tristate "Netdev notifier error injection module" 1485 depends on NET && NOTIFIER_ERROR_INJECTION 1486 help 1487 This option provides the ability to inject artificial errors to 1488 netdevice notifier chain callbacks. It is controlled through debugfs 1489 interface /sys/kernel/debug/notifier-error-inject/netdev 1490 1491 If the notifier call chain should be failed with some events 1492 notified, write the error code to "actions/<notifier event>/error". 1493 1494 Example: Inject netdevice mtu change error (-22 = -EINVAL) 1495 1496 # cd /sys/kernel/debug/notifier-error-inject/netdev 1497 # echo -22 > actions/NETDEV_CHANGEMTU/error 1498 # ip link set eth0 mtu 1024 1499 RTNETLINK answers: Invalid argument 1500 1501 To compile this code as a module, choose M here: the module will 1502 be called netdev-notifier-error-inject. 1503 1504 If unsure, say N. 1505 1506config FAULT_INJECTION 1507 bool "Fault-injection framework" 1508 depends on DEBUG_KERNEL 1509 help 1510 Provide fault-injection framework. 1511 For more details, see Documentation/fault-injection/. 1512 1513config FUNCTION_ERROR_INJECTION 1514 def_bool y 1515 depends on HAVE_FUNCTION_ERROR_INJECTION && KPROBES 1516 1517config FAILSLAB 1518 bool "Fault-injection capability for kmalloc" 1519 depends on FAULT_INJECTION 1520 depends on SLAB || SLUB 1521 help 1522 Provide fault-injection capability for kmalloc. 1523 1524config FAIL_PAGE_ALLOC 1525 bool "Fault-injection capabilitiy for alloc_pages()" 1526 depends on FAULT_INJECTION 1527 help 1528 Provide fault-injection capability for alloc_pages(). 1529 1530config FAIL_MAKE_REQUEST 1531 bool "Fault-injection capability for disk IO" 1532 depends on FAULT_INJECTION && BLOCK 1533 help 1534 Provide fault-injection capability for disk IO. 1535 1536config FAIL_IO_TIMEOUT 1537 bool "Fault-injection capability for faking disk interrupts" 1538 depends on FAULT_INJECTION && BLOCK 1539 help 1540 Provide fault-injection capability on end IO handling. This 1541 will make the block layer "forget" an interrupt as configured, 1542 thus exercising the error handling. 1543 1544 Only works with drivers that use the generic timeout handling, 1545 for others it wont do anything. 1546 1547config FAIL_MMC_REQUEST 1548 bool "Fault-injection capability for MMC IO" 1549 depends on FAULT_INJECTION_DEBUG_FS && MMC 1550 help 1551 Provide fault-injection capability for MMC IO. 1552 This will make the mmc core return data errors. This is 1553 useful to test the error handling in the mmc block device 1554 and to test how the mmc host driver handles retries from 1555 the block device. 1556 1557config FAIL_FUTEX 1558 bool "Fault-injection capability for futexes" 1559 select DEBUG_FS 1560 depends on FAULT_INJECTION && FUTEX 1561 help 1562 Provide fault-injection capability for futexes. 1563 1564config FAIL_FUNCTION 1565 bool "Fault-injection capability for functions" 1566 depends on FAULT_INJECTION_DEBUG_FS && FUNCTION_ERROR_INJECTION 1567 help 1568 Provide function-based fault-injection capability. 1569 This will allow you to override a specific function with a return 1570 with given return value. As a result, function caller will see 1571 an error value and have to handle it. This is useful to test the 1572 error handling in various subsystems. 1573 1574config FAULT_INJECTION_DEBUG_FS 1575 bool "Debugfs entries for fault-injection capabilities" 1576 depends on FAULT_INJECTION && SYSFS && DEBUG_FS 1577 help 1578 Enable configuration of fault-injection capabilities via debugfs. 1579 1580config FAULT_INJECTION_STACKTRACE_FILTER 1581 bool "stacktrace filter for fault-injection capabilities" 1582 depends on FAULT_INJECTION_DEBUG_FS && STACKTRACE_SUPPORT 1583 depends on !X86_64 1584 select STACKTRACE 1585 select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC && !X86 1586 help 1587 Provide stacktrace filter for fault-injection capabilities 1588 1589config LATENCYTOP 1590 bool "Latency measuring infrastructure" 1591 depends on DEBUG_KERNEL 1592 depends on STACKTRACE_SUPPORT 1593 depends on PROC_FS 1594 select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC && !X86 1595 select KALLSYMS 1596 select KALLSYMS_ALL 1597 select STACKTRACE 1598 select SCHEDSTATS 1599 select SCHED_DEBUG 1600 help 1601 Enable this option if you want to use the LatencyTOP tool 1602 to find out which userspace is blocking on what kernel operations. 1603 1604source kernel/trace/Kconfig 1605 1606config PROVIDE_OHCI1394_DMA_INIT 1607 bool "Remote debugging over FireWire early on boot" 1608 depends on PCI && X86 1609 help 1610 If you want to debug problems which hang or crash the kernel early 1611 on boot and the crashing machine has a FireWire port, you can use 1612 this feature to remotely access the memory of the crashed machine 1613 over FireWire. This employs remote DMA as part of the OHCI1394 1614 specification which is now the standard for FireWire controllers. 1615 1616 With remote DMA, you can monitor the printk buffer remotely using 1617 firescope and access all memory below 4GB using fireproxy from gdb. 1618 Even controlling a kernel debugger is possible using remote DMA. 1619 1620 Usage: 1621 1622 If ohci1394_dma=early is used as boot parameter, it will initialize 1623 all OHCI1394 controllers which are found in the PCI config space. 1624 1625 As all changes to the FireWire bus such as enabling and disabling 1626 devices cause a bus reset and thereby disable remote DMA for all 1627 devices, be sure to have the cable plugged and FireWire enabled on 1628 the debugging host before booting the debug target for debugging. 1629 1630 This code (~1k) is freed after boot. By then, the firewire stack 1631 in charge of the OHCI-1394 controllers should be used instead. 1632 1633 See Documentation/debugging-via-ohci1394.txt for more information. 1634 1635config DMA_API_DEBUG 1636 bool "Enable debugging of DMA-API usage" 1637 depends on HAVE_DMA_API_DEBUG 1638 help 1639 Enable this option to debug the use of the DMA API by device drivers. 1640 With this option you will be able to detect common bugs in device 1641 drivers like double-freeing of DMA mappings or freeing mappings that 1642 were never allocated. 1643 1644 This also attempts to catch cases where a page owned by DMA is 1645 accessed by the cpu in a way that could cause data corruption. For 1646 example, this enables cow_user_page() to check that the source page is 1647 not undergoing DMA. 1648 1649 This option causes a performance degradation. Use only if you want to 1650 debug device drivers and dma interactions. 1651 1652 If unsure, say N. 1653 1654menuconfig RUNTIME_TESTING_MENU 1655 bool "Runtime Testing" 1656 def_bool y 1657 1658if RUNTIME_TESTING_MENU 1659 1660config LKDTM 1661 tristate "Linux Kernel Dump Test Tool Module" 1662 depends on DEBUG_FS 1663 depends on BLOCK 1664 default n 1665 help 1666 This module enables testing of the different dumping mechanisms by 1667 inducing system failures at predefined crash points. 1668 If you don't need it: say N 1669 Choose M here to compile this code as a module. The module will be 1670 called lkdtm. 1671 1672 Documentation on how to use the module can be found in 1673 Documentation/fault-injection/provoke-crashes.txt 1674 1675config TEST_LIST_SORT 1676 tristate "Linked list sorting test" 1677 depends on DEBUG_KERNEL || m 1678 help 1679 Enable this to turn on 'list_sort()' function test. This test is 1680 executed only once during system boot (so affects only boot time), 1681 or at module load time. 1682 1683 If unsure, say N. 1684 1685config TEST_SORT 1686 tristate "Array-based sort test" 1687 depends on DEBUG_KERNEL || m 1688 help 1689 This option enables the self-test function of 'sort()' at boot, 1690 or at module load time. 1691 1692 If unsure, say N. 1693 1694config KPROBES_SANITY_TEST 1695 bool "Kprobes sanity tests" 1696 depends on DEBUG_KERNEL 1697 depends on KPROBES 1698 default n 1699 help 1700 This option provides for testing basic kprobes functionality on 1701 boot. A sample kprobe, jprobe and kretprobe are inserted and 1702 verified for functionality. 1703 1704 Say N if you are unsure. 1705 1706config BACKTRACE_SELF_TEST 1707 tristate "Self test for the backtrace code" 1708 depends on DEBUG_KERNEL 1709 default n 1710 help 1711 This option provides a kernel module that can be used to test 1712 the kernel stack backtrace code. This option is not useful 1713 for distributions or general kernels, but only for kernel 1714 developers working on architecture code. 1715 1716 Note that if you want to also test saved backtraces, you will 1717 have to enable STACKTRACE as well. 1718 1719 Say N if you are unsure. 1720 1721config RBTREE_TEST 1722 tristate "Red-Black tree test" 1723 depends on DEBUG_KERNEL 1724 help 1725 A benchmark measuring the performance of the rbtree library. 1726 Also includes rbtree invariant checks. 1727 1728config INTERVAL_TREE_TEST 1729 tristate "Interval tree test" 1730 depends on DEBUG_KERNEL 1731 select INTERVAL_TREE 1732 help 1733 A benchmark measuring the performance of the interval tree library 1734 1735config PERCPU_TEST 1736 tristate "Per cpu operations test" 1737 depends on m && DEBUG_KERNEL 1738 help 1739 Enable this option to build test module which validates per-cpu 1740 operations. 1741 1742 If unsure, say N. 1743 1744config ATOMIC64_SELFTEST 1745 tristate "Perform an atomic64_t self-test" 1746 help 1747 Enable this option to test the atomic64_t functions at boot or 1748 at module load time. 1749 1750 If unsure, say N. 1751 1752config ASYNC_RAID6_TEST 1753 tristate "Self test for hardware accelerated raid6 recovery" 1754 depends on ASYNC_RAID6_RECOV 1755 select ASYNC_MEMCPY 1756 ---help--- 1757 This is a one-shot self test that permutes through the 1758 recovery of all the possible two disk failure scenarios for a 1759 N-disk array. Recovery is performed with the asynchronous 1760 raid6 recovery routines, and will optionally use an offload 1761 engine if one is available. 1762 1763 If unsure, say N. 1764 1765config TEST_HEXDUMP 1766 tristate "Test functions located in the hexdump module at runtime" 1767 1768config TEST_STRING_HELPERS 1769 tristate "Test functions located in the string_helpers module at runtime" 1770 1771config TEST_KSTRTOX 1772 tristate "Test kstrto*() family of functions at runtime" 1773 1774config TEST_PRINTF 1775 tristate "Test printf() family of functions at runtime" 1776 1777config TEST_BITMAP 1778 tristate "Test bitmap_*() family of functions at runtime" 1779 default n 1780 help 1781 Enable this option to test the bitmap functions at boot. 1782 1783 If unsure, say N. 1784 1785config TEST_UUID 1786 tristate "Test functions located in the uuid module at runtime" 1787 1788config TEST_RHASHTABLE 1789 tristate "Perform selftest on resizable hash table" 1790 default n 1791 help 1792 Enable this option to test the rhashtable functions at boot. 1793 1794 If unsure, say N. 1795 1796config TEST_HASH 1797 tristate "Perform selftest on hash functions" 1798 default n 1799 help 1800 Enable this option to test the kernel's integer (<linux/hash.h>), 1801 string (<linux/stringhash.h>), and siphash (<linux/siphash.h>) 1802 hash functions on boot (or module load). 1803 1804 This is intended to help people writing architecture-specific 1805 optimized versions. If unsure, say N. 1806 1807config TEST_PARMAN 1808 tristate "Perform selftest on priority array manager" 1809 default n 1810 depends on PARMAN 1811 help 1812 Enable this option to test priority array manager on boot 1813 (or module load). 1814 1815 If unsure, say N. 1816 1817config TEST_LKM 1818 tristate "Test module loading with 'hello world' module" 1819 default n 1820 depends on m 1821 help 1822 This builds the "test_module" module that emits "Hello, world" 1823 on printk when loaded. It is designed to be used for basic 1824 evaluation of the module loading subsystem (for example when 1825 validating module verification). It lacks any extra dependencies, 1826 and will not normally be loaded by the system unless explicitly 1827 requested by name. 1828 1829 If unsure, say N. 1830 1831config TEST_USER_COPY 1832 tristate "Test user/kernel boundary protections" 1833 default n 1834 depends on m 1835 help 1836 This builds the "test_user_copy" module that runs sanity checks 1837 on the copy_to/from_user infrastructure, making sure basic 1838 user/kernel boundary testing is working. If it fails to load, 1839 a regression has been detected in the user/kernel memory boundary 1840 protections. 1841 1842 If unsure, say N. 1843 1844config TEST_BPF 1845 tristate "Test BPF filter functionality" 1846 default n 1847 depends on m && NET 1848 help 1849 This builds the "test_bpf" module that runs various test vectors 1850 against the BPF interpreter or BPF JIT compiler depending on the 1851 current setting. This is in particular useful for BPF JIT compiler 1852 development, but also to run regression tests against changes in 1853 the interpreter code. It also enables test stubs for eBPF maps and 1854 verifier used by user space verifier testsuite. 1855 1856 If unsure, say N. 1857 1858config FIND_BIT_BENCHMARK 1859 tristate "Test find_bit functions" 1860 default n 1861 help 1862 This builds the "test_find_bit" module that measure find_*_bit() 1863 functions performance. 1864 1865 If unsure, say N. 1866 1867config TEST_FIRMWARE 1868 tristate "Test firmware loading via userspace interface" 1869 default n 1870 depends on FW_LOADER 1871 help 1872 This builds the "test_firmware" module that creates a userspace 1873 interface for testing firmware loading. This can be used to 1874 control the triggering of firmware loading without needing an 1875 actual firmware-using device. The contents can be rechecked by 1876 userspace. 1877 1878 If unsure, say N. 1879 1880config TEST_SYSCTL 1881 tristate "sysctl test driver" 1882 default n 1883 depends on PROC_SYSCTL 1884 help 1885 This builds the "test_sysctl" module. This driver enables to test the 1886 proc sysctl interfaces available to drivers safely without affecting 1887 production knobs which might alter system functionality. 1888 1889 If unsure, say N. 1890 1891config TEST_UDELAY 1892 tristate "udelay test driver" 1893 default n 1894 help 1895 This builds the "udelay_test" module that helps to make sure 1896 that udelay() is working properly. 1897 1898 If unsure, say N. 1899 1900config TEST_STATIC_KEYS 1901 tristate "Test static keys" 1902 default n 1903 depends on m 1904 help 1905 Test the static key interfaces. 1906 1907 If unsure, say N. 1908 1909config TEST_KMOD 1910 tristate "kmod stress tester" 1911 default n 1912 depends on m 1913 depends on BLOCK && (64BIT || LBDAF) # for XFS, BTRFS 1914 depends on NETDEVICES && NET_CORE && INET # for TUN 1915 select TEST_LKM 1916 select XFS_FS 1917 select TUN 1918 select BTRFS_FS 1919 help 1920 Test the kernel's module loading mechanism: kmod. kmod implements 1921 support to load modules using the Linux kernel's usermode helper. 1922 This test provides a series of tests against kmod. 1923 1924 Although technically you can either build test_kmod as a module or 1925 into the kernel we disallow building it into the kernel since 1926 it stress tests request_module() and this will very likely cause 1927 some issues by taking over precious threads available from other 1928 module load requests, ultimately this could be fatal. 1929 1930 To run tests run: 1931 1932 tools/testing/selftests/kmod/kmod.sh --help 1933 1934 If unsure, say N. 1935 1936config TEST_DEBUG_VIRTUAL 1937 tristate "Test CONFIG_DEBUG_VIRTUAL feature" 1938 depends on DEBUG_VIRTUAL 1939 help 1940 Test the kernel's ability to detect incorrect calls to 1941 virt_to_phys() done against the non-linear part of the 1942 kernel's virtual address map. 1943 1944 If unsure, say N. 1945 1946endif # RUNTIME_TESTING_MENU 1947 1948config MEMTEST 1949 bool "Memtest" 1950 depends on HAVE_MEMBLOCK 1951 ---help--- 1952 This option adds a kernel parameter 'memtest', which allows memtest 1953 to be set. 1954 memtest=0, mean disabled; -- default 1955 memtest=1, mean do 1 test pattern; 1956 ... 1957 memtest=17, mean do 17 test patterns. 1958 If you are unsure how to answer this question, answer N. 1959 1960config BUG_ON_DATA_CORRUPTION 1961 bool "Trigger a BUG when data corruption is detected" 1962 select DEBUG_LIST 1963 help 1964 Select this option if the kernel should BUG when it encounters 1965 data corruption in kernel memory structures when they get checked 1966 for validity. 1967 1968 If unsure, say N. 1969 1970source "samples/Kconfig" 1971 1972source "lib/Kconfig.kgdb" 1973 1974source "lib/Kconfig.ubsan" 1975 1976config ARCH_HAS_DEVMEM_IS_ALLOWED 1977 bool 1978 1979config STRICT_DEVMEM 1980 bool "Filter access to /dev/mem" 1981 depends on MMU && DEVMEM 1982 depends on ARCH_HAS_DEVMEM_IS_ALLOWED 1983 default y if PPC || X86 || ARM64 1984 ---help--- 1985 If this option is disabled, you allow userspace (root) access to all 1986 of memory, including kernel and userspace memory. Accidental 1987 access to this is obviously disastrous, but specific access can 1988 be used by people debugging the kernel. Note that with PAT support 1989 enabled, even in this case there are restrictions on /dev/mem 1990 use due to the cache aliasing requirements. 1991 1992 If this option is switched on, and IO_STRICT_DEVMEM=n, the /dev/mem 1993 file only allows userspace access to PCI space and the BIOS code and 1994 data regions. This is sufficient for dosemu and X and all common 1995 users of /dev/mem. 1996 1997 If in doubt, say Y. 1998 1999config IO_STRICT_DEVMEM 2000 bool "Filter I/O access to /dev/mem"
2001 depends on STRICT_DEVMEM 2002 ---help--- 2003 If this option is disabled, you allow userspace (root) access to all 2004 io-memory regardless of whether a driver is actively using that 2005 range. Accidental access to this is obviously disastrous, but 2006 specific access can be used by people debugging kernel drivers. 2007 2008 If this option is switched on, the /dev/mem file only allows 2009 userspace access to *idle* io-memory ranges (see /proc/iomem) This 2010 may break traditional users of /dev/mem (dosemu, legacy X, etc...) 2011 if the driver using a given range cannot be disabled. 2012 2013 If in doubt, say Y. 2014