From: Frederic Weisbecker frederic@kernel.org
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@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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/time/timer.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-)
--- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -580,7 +580,15 @@ 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); }
@@ -899,10 +907,13 @@ 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 }