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panic: use atomic_try_cmpxchg in panic() and nmi_panic() 

Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old
in panic() and nmi_panic().  x86 CMPXCHG instruction returns success in ZF
flag, so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).

Also, rename cpu variable to this_cpu in nmi_panic() and try to unify
logic flow between panic() and nmi_panic().

No functional change intended.

[ubizjak@gmail.com: clean up if/else block]
  Link: https://lkml.kernel.org/r/20230906191200.68707-1-ubizjak@gmail.com
Link: https://lkml.kernel.org/r/20230904152230.9227-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Uros Bizjak 2023-09-04 17:21:01 +02:00 committed by Andrew Morton
parent 3983520491
commit 9734fe4dc2
1 changed files with 13 additions and 9 deletions
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22
kernel/panic.c
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@ -192,14 +192,15 @@ atomic_t panic_cpu = ATOMIC_INIT(PANIC_CPU_INVALID);
*/ */
void nmi_panic(struct pt_regs *regs, const char *msg) void nmi_panic(struct pt_regs *regs, const char *msg)
{ {
int old_cpu, cpu; int old_cpu, this_cpu;
cpu = raw_smp_processor_id(); old_cpu = PANIC_CPU_INVALID;
old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, cpu); this_cpu = raw_smp_processor_id();
if (old_cpu == PANIC_CPU_INVALID) /* atomic_try_cmpxchg updates old_cpu on failure */
if (atomic_try_cmpxchg(&panic_cpu, &old_cpu, this_cpu))
panic("%s", msg); panic("%s", msg);
else if (old_cpu != cpu) else if (old_cpu != this_cpu)
nmi_panic_self_stop(regs); nmi_panic_self_stop(regs);
} }
EXPORT_SYMBOL(nmi_panic); EXPORT_SYMBOL(nmi_panic);
@ -311,15 +312,18 @@ void panic(const char *fmt, ...)
* stop themself or will wait until they are stopped by the 1st CPU * stop themself or will wait until they are stopped by the 1st CPU
* with smp_send_stop(). * with smp_send_stop().
* *
* `old_cpu == PANIC_CPU_INVALID' means this is the 1st CPU which * cmpxchg success means this is the 1st CPU which comes here,
* comes here, so go ahead. * so go ahead.
* `old_cpu == this_cpu' means we came from nmi_panic() which sets * `old_cpu == this_cpu' means we came from nmi_panic() which sets
* panic_cpu to this CPU. In this case, this is also the 1st CPU. * panic_cpu to this CPU. In this case, this is also the 1st CPU.
*/ */
old_cpu = PANIC_CPU_INVALID;
this_cpu = raw_smp_processor_id(); this_cpu = raw_smp_processor_id();
old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu);
if (old_cpu != PANIC_CPU_INVALID && old_cpu != this_cpu) /* atomic_try_cmpxchg updates old_cpu on failure */
if (atomic_try_cmpxchg(&panic_cpu, &old_cpu, this_cpu)) {
/* go ahead */
} else if (old_cpu != this_cpu)
panic_smp_self_stop(); panic_smp_self_stop();
console_verbose(); console_verbose();