6.6-stable review patch. If anyone has any objections, please let me know.
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From: Frederic Weisbecker frederic@kernel.org
[ Upstream commit 3ce74f1a8566dbbc9774f85fb0ce781fe290fd32 ]
tick_nohz_idle_got_tick() is called by cpuidle_reflect() within the idle loop with interrupts enabled. This function modifies the struct tick_sched's bitfield "got_idle_tick". However this bitfield is stored within the same mask as other bitfields that can be modified from interrupts.
Fortunately so far it looks like the only race that can happen is while writing ->got_idle_tick to 0, an interrupt fires and writes the ->idle_active field to 0. It's then possible that the interrupted write to ->got_idle_tick writes back the old value of ->idle_active back to 1.
However if that happens, the worst possible outcome is that the time spent between that interrupt and the upcoming call to tick_nohz_idle_exit() is accounted as idle, which is negligible quantity.
Still all the bitfield writes within this struct tick_sched's shadow mask should be IRQ-safe. Therefore move this bitfield out to its own storage to avoid further suprises.
Signed-off-by: Frederic Weisbecker frederic@kernel.org Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Thomas Gleixner tglx@linutronix.de Link: https://lore.kernel.org/r/20240225225508.11587-12-frederic@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/time/tick-sched.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h index 5ed5a9d41d5a7..03a586e12cf89 100644 --- a/kernel/time/tick-sched.h +++ b/kernel/time/tick-sched.h @@ -61,7 +61,6 @@ struct tick_sched { unsigned int tick_stopped : 1; unsigned int idle_active : 1; unsigned int do_timer_last : 1; - unsigned int got_idle_tick : 1;
/* Tick handling: jiffies stall check */ unsigned int stalled_jiffies; @@ -73,6 +72,7 @@ struct tick_sched { ktime_t next_tick; unsigned long idle_jiffies; ktime_t idle_waketime; + unsigned int got_idle_tick;
/* Idle entry */ seqcount_t idle_sleeptime_seq;