linux-kernel - [PATCH] fork: Use this_cpu_try_cmpxchg() in try_release_thread_stack_to

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Date: Thu, 23 May 2024 09:35:14 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: linux-kernel@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] fork: Use this_cpu_try_cmpxchg() in try_release_thread_stack_to_cache()

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.

Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
---
 kernel/fork.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 99076dbe27d8..c9e994d66930 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -205,7 +205,9 @@ 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)
+		struct vm_struct *tmp = NULL;
+
+		if (!this_cpu_try_cmpxchg(cached_stacks[i], &tmp, vm))
 			continue;
 		return true;
 	}
-- 
2.45.1