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fork: use this_cpu_try_cmpxchg() in try_release_thread_stack_to_cache()

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

No functional change intended.

[ubizjak@gmail.com: simplify the for loop a bit]
  Link: https://lkml.kernel.org/r/20240523214442.21102-1-ubizjak@gmail.com
Link: https://lkml.kernel.org/r/20240523073530.8128-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Uros Bizjak 2024-05-23 09:35:14 +02:00 committed by Andrew Morton
parent af77c4fc18
commit 47e39c7933
1 changed files with 4 additions and 3 deletions
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kernel/fork.c
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@ -205,9 +205,10 @@ static bool try_release_thread_stack_to_cache(struct vm_struct *vm)
unsigned int i;
for (i = 0; i < NR_CACHED_STACKS; i++) {
if (this_cpu_cmpxchg(cached_stacks[i], NULL, vm) != NULL)
continue;
return true;
struct vm_struct *tmp = NULL;
if (this_cpu_try_cmpxchg(cached_stacks[i], &tmp, vm))
return true;
}
return false;
}