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

Commit-ID: 30c66fc30ee7a98c4f3adf5fb7e213b61884474f Gitweb: https://git.kernel.org/tip/30c66fc30ee7a98c4f3adf5fb7e213b61884474f Author: Frederic Weisbecker frederic@kernel.org AuthorDate: Fri, 03 Jul 2020 03:06:57 +02:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Thu, 09 Jul 2020 11:56:57 +02:00

timer: Prevent base->clk from moving backward

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@kernel.org Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Anna-Maria Behnsen anna-maria@linutronix.de Tested-by: Juri Lelli juri.lelli@redhat.com Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20200703010657.2302-1-frederic@kernel.org --- kernel/time/timer.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 398e6ea..9a838d3 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -584,7 +584,15 @@ trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer) * 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); }

@@ -896,10 +904,13 @@ static inline void forward_timer_base(struct timer_base *base) * 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 }