// SPDX-License-Identifier: GPL-2.0
#define CREATE_TRACE_POINTS
#include <trace/events/mmap_lock.h>

#include <linux/mm.h>
#include <linux/cgroup.h>
#include <linux/memcontrol.h>
#include <linux/mmap_lock.h>
#include <linux/mutex.h>
#include <linux/percpu.h>
#include <linux/rcupdate.h>
#include <linux/smp.h>
#include <linux/trace_events.h>

EXPORT_TRACEPOINT_SYMBOL(mmap_lock_start_locking);
EXPORT_TRACEPOINT_SYMBOL(mmap_lock_acquire_returned);
EXPORT_TRACEPOINT_SYMBOL(mmap_lock_released);

#ifdef CONFIG_MEMCG

/*
 * Our various events all share the same buffer (because we don't want or need
 * to allocate a set of buffers *per event type*), so we need to protect against
 * concurrent _reg() and _unreg() calls, and count how many _reg() calls have
 * been made.
 */
static DEFINE_MUTEX(reg_lock);
static int reg_refcount; /* Protected by reg_lock. */

/*
 * Size of the buffer for memcg path names. Ignoring stack trace support,
 * trace_events_hist.c uses MAX_FILTER_STR_VAL for this, so we also use it.
 */
#define MEMCG_PATH_BUF_SIZE MAX_FILTER_STR_VAL

/*
 * How many contexts our trace events might be called in: normal, softirq, irq,
 * and NMI.
 */
#define CONTEXT_COUNT 4

static DEFINE_PER_CPU(char __rcu *, memcg_path_buf);
static char **tmp_bufs;
static DEFINE_PER_CPU(int, memcg_path_buf_idx);

/* Called with reg_lock held. */
static void free_memcg_path_bufs(void)
{
        int cpu;
        char **old = tmp_bufs;

        for_each_possible_cpu(cpu) {
                *(old++) = rcu_dereference_protected(
                        per_cpu(memcg_path_buf, cpu),
                        lockdep_is_held(&reg_lock));
                rcu_assign_pointer(per_cpu(memcg_path_buf, cpu), NULL);
        }

        /* Wait for inflight memcg_path_buf users to finish. */
        synchronize_rcu();

        old = tmp_bufs;
        for_each_possible_cpu(cpu) {
                kfree(*(old++));
        }

        kfree(tmp_bufs);
        tmp_bufs = NULL;
}

int trace_mmap_lock_reg(void)
{
        int cpu;
        char *new;

        mutex_lock(&reg_lock);

        /* If the refcount is going 0->1, proceed with allocating buffers. */
        if (reg_refcount++)
                goto out;

        tmp_bufs = kmalloc_array(num_possible_cpus(), sizeof(*tmp_bufs),
                                 GFP_KERNEL);
        if (tmp_bufs == NULL)
                goto out_fail;

        for_each_possible_cpu(cpu) {
                new = kmalloc(MEMCG_PATH_BUF_SIZE * CONTEXT_COUNT, GFP_KERNEL);
                if (new == NULL)
                        goto out_fail_free;
                rcu_assign_pointer(per_cpu(memcg_path_buf, cpu), new);
                /* Don't need to wait for inflights, they'd have gotten NULL. */
        }

out:
        mutex_unlock(&reg_lock);
        return 0;

out_fail_free:
        free_memcg_path_bufs();
out_fail:
        /* Since we failed, undo the earlier ref increment. */
        --reg_refcount;

        mutex_unlock(&reg_lock);
        return -ENOMEM;
}

void trace_mmap_lock_unreg(void)
{
        mutex_lock(&reg_lock);

        /* If the refcount is going 1->0, proceed with freeing buffers. */
        if (--reg_refcount)
                goto out;

        free_memcg_path_bufs();

out:
        mutex_unlock(&reg_lock);
}

static inline char *get_memcg_path_buf(void)
{
        char *buf;
        int idx;

        rcu_read_lock();
        buf = rcu_dereference(*this_cpu_ptr(&memcg_path_buf));
        if (buf == NULL) {
                rcu_read_unlock();
                return NULL;
        }
        idx = this_cpu_add_return(memcg_path_buf_idx, MEMCG_PATH_BUF_SIZE) -
              MEMCG_PATH_BUF_SIZE;
        return &buf[idx];
}

static inline void put_memcg_path_buf(void)
{
        this_cpu_sub(memcg_path_buf_idx, MEMCG_PATH_BUF_SIZE);
        rcu_read_unlock();
}

/*
 * Write the given mm_struct's memcg path to a percpu buffer, and return a
 * pointer to it. If the path cannot be determined, or no buffer was available
 * (because the trace event is being unregistered), NULL is returned.
 *
 * Note: buffers are allocated per-cpu to avoid locking, so preemption must be
 * disabled by the caller before calling us, and re-enabled only after the
 * caller is done with the pointer.
 *
 * The caller must call put_memcg_path_buf() once the buffer is no longer
 * needed. This must be done while preemption is still disabled.
 */
static const char *get_mm_memcg_path(struct mm_struct *mm)
{
        char *buf = NULL;
        struct mem_cgroup *memcg = get_mem_cgroup_from_mm(mm);

        if (memcg == NULL)
                goto out;
        if (unlikely(memcg->css.cgroup == NULL))
                goto out_put;

        buf = get_memcg_path_buf();
        if (buf == NULL)
                goto out_put;

        cgroup_path(memcg->css.cgroup, buf, MEMCG_PATH_BUF_SIZE);

out_put:
        css_put(&memcg->css);
out:
        return buf;
}

#define TRACE_MMAP_LOCK_EVENT(type, mm, ...)                                   \
        do {                                                                   \
                const char *memcg_path;                                        \
                preempt_disable();                                             \
                memcg_path = get_mm_memcg_path(mm);                            \
                trace_mmap_lock_##type(mm,                                     \
                                       memcg_path != NULL ? memcg_path : "",   \
                                       ##__VA_ARGS__);                         \
                if (likely(memcg_path != NULL))                                \
                        put_memcg_path_buf();                                  \
                preempt_enable();                                              \
        } while (0)

#else /* !CONFIG_MEMCG */

int trace_mmap_lock_reg(void)
{
        return 0;
}

void trace_mmap_lock_unreg(void)
{
}

#define TRACE_MMAP_LOCK_EVENT(type, mm, ...)                                   \
        trace_mmap_lock_##type(mm, "", ##__VA_ARGS__)

#endif /* CONFIG_MEMCG */

/*
 * Trace calls must be in a separate file, as otherwise there's a circular
 * dependency between linux/mmap_lock.h and trace/events/mmap_lock.h.
 */

void __mmap_lock_do_trace_start_locking(struct mm_struct *mm, bool write)
{
        TRACE_MMAP_LOCK_EVENT(start_locking, mm, write);
}
EXPORT_SYMBOL(__mmap_lock_do_trace_start_locking);

void __mmap_lock_do_trace_acquire_returned(struct mm_struct *mm, bool write,
                                           bool success)
{
        TRACE_MMAP_LOCK_EVENT(acquire_returned, mm, write, success);
}
EXPORT_SYMBOL(__mmap_lock_do_trace_acquire_returned);

void __mmap_lock_do_trace_released(struct mm_struct *mm, bool write)
{
        TRACE_MMAP_LOCK_EVENT(released, mm, write);
}
EXPORT_SYMBOL(__mmap_lock_do_trace_released);