treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 135
[sfrench/cifs-2.6.git] / drivers / xen / preempt.c
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * Preemptible hypercalls
4  *
5  * Copyright (C) 2014 Citrix Systems R&D ltd.
6  */
7
8 #include <linux/sched.h>
9 #include <xen/xen-ops.h>
10
11 #ifndef CONFIG_PREEMPT
12
13 /*
14  * Some hypercalls issued by the toolstack can take many 10s of
15  * seconds. Allow tasks running hypercalls via the privcmd driver to
16  * be voluntarily preempted even if full kernel preemption is
17  * disabled.
18  *
19  * Such preemptible hypercalls are bracketed by
20  * xen_preemptible_hcall_begin() and xen_preemptible_hcall_end()
21  * calls.
22  */
23
24 DEFINE_PER_CPU(bool, xen_in_preemptible_hcall);
25 EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
26
27 asmlinkage __visible void xen_maybe_preempt_hcall(void)
28 {
29         if (unlikely(__this_cpu_read(xen_in_preemptible_hcall)
30                      && need_resched())) {
31                 /*
32                  * Clear flag as we may be rescheduled on a different
33                  * cpu.
34                  */
35                 __this_cpu_write(xen_in_preemptible_hcall, false);
36                 _cond_resched();
37                 __this_cpu_write(xen_in_preemptible_hcall, true);
38         }
39 }
40 #endif /* CONFIG_PREEMPT */