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authorFrederic Weisbecker <frederic@kernel.org>2020-07-03 03:06:57 +0200
committerThomas Gleixner <tglx@linutronix.de>2020-07-09 11:56:57 +0200
commit30c66fc30ee7a98c4f3adf5fb7e213b61884474f (patch)
tree1fc8c5174e08d76f9f7d7533c80face852479bb0 /kernel/time
parentdcb7fd82c75ee2d6e6f9d8cc71c52519ed52e258 (diff)
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
Diffstat (limited to 'kernel/time')
-rw-r--r--kernel/time/timer.c17
1 files changed, 14 insertions, 3 deletions
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 398e6eadb861..9a838d38dbe6 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
}