LXR linux/drivers/xen/preempt.c

   1/*
   2 * Preemptible hypercalls
   3 *
   4 * Copyright (C) 2014 Citrix Systems R&D ltd.
   5 *
   6 * This source code is free software; you can redistribute it and/or
   7 * modify it under the terms of the GNU General Public License as
   8 * published by the Free Software Foundation; either version 2 of the
   9 * License, or (at your option) any later version.
  10 */
  11
  12#include <linux/sched.h>
  13#include <xen/xen-ops.h>
  14
  15#ifndef CONFIG_PREEMPT
  16
  17/*
  18 * Some hypercalls issued by the toolstack can take many 10s of
  19 * seconds. Allow tasks running hypercalls via the privcmd driver to
  20 * be voluntarily preempted even if full kernel preemption is
  21 * disabled.
  22 *
  23 * Such preemptible hypercalls are bracketed by
  24 * xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
  25 * calls.
  26 */
  27
  28DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
  29EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
  30
  31asmlinkage __visible void xen_maybe_preempt_hcall(void)
  32{
  33        if (unlikely(__this_cpu_read(xen_in_preemptible_hcall)
  34                     && need_resched())) {
  35                /*
  36                 * Clear flag as we may be rescheduled on a different
  37                 * cpu.
  38                 */
  39                __this_cpu_write(xen_in_preemptible_hcall, false);
  40                _cond_resched();
  41                __this_cpu_write(xen_in_preemptible_hcall, true);
  42        }
  43}
  44#endif /* CONFIG_PREEMPT */
  45