linux-kernel - [tip: locking/core] locking/spinlock/debug: Fix data-race in do_raw_write

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Message-ID: <176104293117.2601451.6475877416936398769.tip-bot2@tip-bot2>
Date: Tue, 21 Oct 2025 10:35:31 -0000
From: "tip-bot2 for Alexander Sverdlin" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Adrian Freihofer <adrian.freihofer@...mens.com>,
 Alexander Sverdlin <alexander.sverdlin@...mens.com>,
 Boqun Feng <boqun.feng@...il.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 "Paul E. McKenney" <paulmck@...nel.org>, Waiman Long <longman@...hat.com>,
 stable@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: locking/core] locking/spinlock/debug: Fix data-race in
 do_raw_write_lock

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     c14ecb555c3ee80eeb030a4e46d00e679537f03a
Gitweb:        https://git.kernel.org/tip/c14ecb555c3ee80eeb030a4e46d00e679537f03a
Author:        Alexander Sverdlin <alexander.sverdlin@...mens.com>
AuthorDate:    Fri, 19 Sep 2025 11:12:38 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 21 Oct 2025 12:31:55 +02:00

locking/spinlock/debug: Fix data-race in do_raw_write_lock

KCSAN reports:

BUG: KCSAN: data-race in do_raw_write_lock / do_raw_write_lock

write (marked) to 0xffff800009cf504c of 4 bytes by task 1102 on cpu 1:
 do_raw_write_lock+0x120/0x204
 _raw_write_lock_irq
 do_exit
 call_usermodehelper_exec_async
 ret_from_fork

read to 0xffff800009cf504c of 4 bytes by task 1103 on cpu 0:
 do_raw_write_lock+0x88/0x204
 _raw_write_lock_irq
 do_exit
 call_usermodehelper_exec_async
 ret_from_fork

value changed: 0xffffffff -> 0x00000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1103 Comm: kworker/u4:1 6.1.111

Commit 1a365e822372 ("locking/spinlock/debug: Fix various data races") has
adressed most of these races, but seems to be not consistent/not complete.

>>From do_raw_write_lock() only debug_write_lock_after() part has been
converted to WRITE_ONCE(), but not debug_write_lock_before() part.
Do it now.

Fixes: 1a365e822372 ("locking/spinlock/debug: Fix various data races")
Reported-by: Adrian Freihofer <adrian.freihofer@...mens.com>
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@...mens.com>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Paul E. McKenney <paulmck@...nel.org>
Acked-by: Waiman Long <longman@...hat.com>
Cc: stable@...r.kernel.org
---
 kernel/locking/spinlock_debug.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/spinlock_debug.c b/kernel/locking/spinlock_debug.c
index 87b03d2..2338b3a 100644
--- a/kernel/locking/spinlock_debug.c
+++ b/kernel/locking/spinlock_debug.c
@@ -184,8 +184,8 @@ void do_raw_read_unlock(rwlock_t *lock)
 static inline void debug_write_lock_before(rwlock_t *lock)
 {
 	RWLOCK_BUG_ON(lock->magic != RWLOCK_MAGIC, lock, "bad magic");
-	RWLOCK_BUG_ON(lock->owner == current, lock, "recursion");
-	RWLOCK_BUG_ON(lock->owner_cpu == raw_smp_processor_id(),
+	RWLOCK_BUG_ON(READ_ONCE(lock->owner) == current, lock, "recursion");
+	RWLOCK_BUG_ON(READ_ONCE(lock->owner_cpu) == raw_smp_processor_id(),
 							lock, "cpu recursion");
 }