The patch titled
Subject: fork: use this_cpu_try_cmpxchg() in try_release_thread_stack_to_cache()
has been added to the -mm mm-nonmm-unstable branch. Its filename is
fork-use-this_cpu_try_cmpxchg-in-try_release_thread_stack_to_cache.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fork-use-this_cpu_try_cmpxchg-in-try_release_thread_stack_to_cache.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Uros Bizjak <ubizjak@xxxxxxxxx>
Subject: fork: use this_cpu_try_cmpxchg() in try_release_thread_stack_to_cache()
Date: Thu, 23 May 2024 09:35:14 +0200
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.
Link: https://lkml.kernel.org/r/20240523073530.8128-1-ubizjak@xxxxxxxxx
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/fork.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
--- a/kernel/fork.c~fork-use-this_cpu_try_cmpxchg-in-try_release_thread_stack_to_cache
+++ a/kernel/fork.c
@@ -205,7 +205,9 @@ static bool try_release_thread_stack_to_
unsigned int i;
for (i = 0; i < NR_CACHED_STACKS; i++) {
- if (this_cpu_cmpxchg(cached_stacks[i], NULL, vm) != NULL)
+ struct vm_struct *tmp = NULL;
+
+ if (!this_cpu_try_cmpxchg(cached_stacks[i], &tmp, vm))
continue;
return true;
}
_
Patches currently in -mm which might be from ubizjak@xxxxxxxxx are
fork-use-this_cpu_try_cmpxchg-in-try_release_thread_stack_to_cache.patch
