linux-kernel - timers: Add missing READ_ONCE() in __run_timer

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Message-ID: <87a5emyqk0.ffs@tglx>
Date: Wed, 30 Oct 2024 08:53:51 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: kernel test robot <oliver.sang@...el.com>, Anna-Maria Behnsen
 <anna-maria@...utronix.de>
Cc: oe-lkp@...ts.linux.dev, lkp@...el.com, linux-kernel@...r.kernel.org,
 Frederic Weisbecker <frederic@...nel.org>, oliver.sang@...el.com
Subject: timers: Add missing READ_ONCE() in __run_timer_base()

__run_timer_base() checks base::next_expiry without holding
base::lock. That can race with a remote CPU updating next_expiry under the
lock. This is an intentional and harmless data race, but lacks a
READ_ONCE(), so KCSAN complains about this.

Add the missing READ_ONCE(). All other places are covered already.

Fixes: 79f8b28e85f8 ("timers: Annotate possible non critical data race of next_expiry")
Reported-by: kernel test robot <oliver.sang@...el.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Closes: https://lore.kernel.org/oe-lkp/202410301205.ef8e9743-lkp@intel.com
---
 kernel/time/timer.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -2422,7 +2422,8 @@ static inline void __run_timers(struct t
 
 static void __run_timer_base(struct timer_base *base)
 {
-	if (time_before(jiffies, base->next_expiry))
+	/* Can race against a remote CPU updating next_expiry under the lock */
+	if (time_before(jiffies, READ_ONCE(base->next_expiry)))
 		return;
 
 	timer_base_lock_expiry(base);