diff options
author | Frederic Weisbecker <frederic@kernel.org> | 2020-07-03 03:06:57 +0200 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-07-22 09:32:11 +0200 |
commit | e68e2c661aa2cda521f1bf6e679f2a919ed5de5f (patch) | |
tree | 38f18d3028c3198b263a9453bb41b9f7222e5ceb | |
parent | 53219e81bb93819769efb263d8be5e3db7cca87a (diff) |
timer: Prevent base->clk from moving backward
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>
-rw-r--r-- | kernel/time/timer.c | 17 |
1 files changed, 14 insertions, 3 deletions
diff --git a/kernel/time/timer.c b/kernel/time/timer.c index ae64cb819a9a..665c876d9137 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -580,7 +580,15 @@ 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); } @@ -899,10 +907,13 @@ 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 } |