This is a note to let you know that I've just added the patch titled timer: Prevent base->clk from moving backward to the 5.7-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: timer-prevent-base-clk-from-moving-backward.patch and it can be found in the queue-5.7 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 30c66fc30ee7a98c4f3adf5fb7e213b61884474f Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker <frederic@xxxxxxxxxx> Date: Fri, 3 Jul 2020 03:06:57 +0200 Subject: timer: Prevent base->clk from moving backward From: Frederic Weisbecker <frederic@xxxxxxxxxx> commit 30c66fc30ee7a98c4f3adf5fb7e213b61884474f upstream. When a timer is enqueued with a negative delta (ie: expiry is below base->clk), it gets added to the wheel as expiring now (base->clk). Yet the value that gets stored in base->next_expiry, while calling trigger_dyntick_cpu(), is the initial timer->expires value. The resulting state becomes: base->next_expiry < base->clk On the next timer enqueue, forward_timer_base() may accidentally rewind base->clk. As a possible outcome, timers may expire way too early, the worst case being that the highest wheel levels get spuriously processed again. To prevent from that, make sure that base->next_expiry doesn't get below base->clk. Fixes: a683f390b93f ("timers: Forward the wheel clock whenever possible") Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Reviewed-by: Anna-Maria Behnsen <anna-maria@xxxxxxxxxxxxx> Tested-by: Juri Lelli <juri.lelli@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Link: https://lkml.kernel.org/r/20200703010657.2302-1-frederic@xxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/time/timer.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -585,7 +585,15 @@ trigger_dyntick_cpu(struct timer_base *b * Set the next expiry time and kick the CPU so it can reevaluate the * wheel: */ - base->next_expiry = timer->expires; + if (time_before(timer->expires, base->clk)) { + /* + * Prevent from forward_timer_base() moving the base->clk + * backward + */ + base->next_expiry = base->clk; + } else { + base->next_expiry = timer->expires; + } wake_up_nohz_cpu(base->cpu); } @@ -897,10 +905,13 @@ static inline void forward_timer_base(st * If the next expiry value is > jiffies, then we fast forward to * jiffies otherwise we forward to the next expiry value. */ - if (time_after(base->next_expiry, jnow)) + if (time_after(base->next_expiry, jnow)) { base->clk = jnow; - else + } else { + if (WARN_ON_ONCE(time_before(base->next_expiry, base->clk))) + return; base->clk = base->next_expiry; + } #endif } Patches currently in stable-queue which might be from frederic@xxxxxxxxxx are queue-5.7/timer-fix-wheel-index-calculation-on-last-level.patch queue-5.7/timer-prevent-base-clk-from-moving-backward.patch