+ fork-use-this_cpu_try_cmpxchg-in-try_release_thread_stack_to_cache.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

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@gmail.com>
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@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>
---

 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@gmail.com are

fork-use-this_cpu_try_cmpxchg-in-try_release_thread_stack_to_cache.patch