__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@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.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);

On Wed, Oct 30, 2024 at 08:53:51AM +0100, Thomas Gleixner wrote:
> __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@intel.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Closes: https://lore.kernel.org/oe-lkp/202410301205.ef8e9743-lkp@intel.com

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

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

Commit-ID:     1d4199cbbe95efaba51304cfd844bd0ccd224e61
Gitweb:        https://git.kernel.org/tip/1d4199cbbe95efaba51304cfd844bd0ccd224e61
Author:        Thomas Gleixner <tglx@linutronix.de>
AuthorDate:    Wed, 30 Oct 2024 08:53:51 +01:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Thu, 31 Oct 2024 11:45:01 +01:00

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@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/all/87a5emyqk0.ffs@tglx
Closes: https://lore.kernel.org/oe-lkp/202410301205.ef8e9743-lkp@intel.com
---
 kernel/time/timer.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 02355b2..a283e52 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -2421,7 +2421,8 @@ static inline void __run_timers(struct timer_base *base)
 
 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);