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kexec: use atomic_try_cmpxchg in crash_kexec

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Use atomic_try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
crash_kexec().  x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after cmpxchg.

No functional change intended.

Link: https://lkml.kernel.org/r/20231114161228.108516-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Uros Bizjak 2023-11-14 17:12:01 +01:00 committed by Andrew Morton
parent 1ee918ffa6
commit 0311d82724
1 changed files with 3 additions and 2 deletions
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5
kernel/kexec_core.c
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@ -1063,9 +1063,10 @@ __bpf_kfunc void crash_kexec(struct pt_regs *regs)
* panic(). Otherwise parallel calls of panic() and crash_kexec()
* may stop each other. To exclude them, we use panic_cpu here too.
*/
old_cpu = PANIC_CPU_INVALID;
this_cpu = raw_smp_processor_id();
old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu);
if (old_cpu == PANIC_CPU_INVALID) {
if (atomic_try_cmpxchg(&panic_cpu, &old_cpu, this_cpu)) {
/* This is the 1st CPU which comes here, so go ahead. */
__crash_kexec(regs);