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
  28 DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
  29 EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
  30
  31 asmlinkage __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 */