The patch titled
Subject: kexec: Use atomic_try_cmpxchg in crash_kexec
has been added to the -mm mm-nonmm-unstable branch. Its filename is
kexec-use-atomic_try_cmpxchg-in-crash_kexec.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kexec-use-atomic_try_cmpxchg-in-crash_kexec.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: kexec: Use atomic_try_cmpxchg in crash_kexec
Date: Tue, 14 Nov 2023 17:12:01 +0100
Use atomic_try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
crash_kexec(). x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after cmpxchg.
No functional change intended.
Link: https://lkml.kernel.org/r/20231114161228.108516-1-ubizjak@xxxxxxxxx
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Acked-by: Baoquan He <bhe@xxxxxxxxxx>
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/kexec_core.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
--- a/kernel/kexec_core.c~kexec-use-atomic_try_cmpxchg-in-crash_kexec
+++ a/kernel/kexec_core.c
@@ -1063,9 +1063,10 @@ __bpf_kfunc void crash_kexec(struct pt_r
* panic(). Otherwise parallel calls of panic() and crash_kexec()
* may stop each other. To exclude them, we use panic_cpu here too.
*/
+ old_cpu = PANIC_CPU_INVALID;
this_cpu = raw_smp_processor_id();
- old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu);
- if (old_cpu == PANIC_CPU_INVALID) {
+
+ if (atomic_try_cmpxchg(&panic_cpu, &old_cpu, this_cpu)) {
/* This is the 1st CPU which comes here, so go ahead. */
__crash_kexec(regs);
_
Patches currently in -mm which might be from ubizjak@xxxxxxxxx are
kexec-use-atomic_try_cmpxchg-in-crash_kexec.patch
