linux-kernel - [PATCH bpf-next v2 03/26] locking: Allow obtaining result of arch_mcs_spin_lock

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Message-ID: <20250206105435.2159977-4-memxor@gmail.com>
Date: Thu,  6 Feb 2025 02:54:11 -0800
From: Kumar Kartikeya Dwivedi <memxor@...il.com>
To: bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Barret Rhoden <brho@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Will Deacon <will@...nel.org>,
	Waiman Long <llong@...hat.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Martin KaFai Lau <martin.lau@...nel.org>,
	Eduard Zingerman <eddyz87@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Tejun Heo <tj@...nel.org>,
	Josh Don <joshdon@...gle.com>,
	Dohyun Kim <dohyunkim@...gle.com>,
	linux-arm-kernel@...ts.infradead.org,
	kernel-team@...a.com
Subject: [PATCH bpf-next v2 03/26] locking: Allow obtaining result of arch_mcs_spin_lock_contended

To support upcoming changes that require inspecting the return value
once the conditional waiting loop in arch_mcs_spin_lock_contended
terminates, modify the macro to preserve the result of
smp_cond_load_acquire. This enables checking the return value as needed,
which will help disambiguate the MCS node’s locked state in future
patches.

Reviewed-by: Barret Rhoden <brho@...gle.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
---
 kernel/locking/mcs_spinlock.h | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h
index 16160ca8907f..5c92ba199b90 100644
--- a/kernel/locking/mcs_spinlock.h
+++ b/kernel/locking/mcs_spinlock.h
@@ -24,9 +24,7 @@
  * spinning, and smp_cond_load_acquire() provides that behavior.
  */
 #define arch_mcs_spin_lock_contended(l)					\
-do {									\
-	smp_cond_load_acquire(l, VAL);					\
-} while (0)
+	smp_cond_load_acquire(l, VAL)
 #endif
 
 #ifndef arch_mcs_spin_unlock_contended
-- 
2.43.5