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timer: Fix wheel index calculation on last level

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When an expiration delta falls into the last level of the wheel, that delta
has be compared against the maximum possible delay and reduced to fit in if
necessary.

However instead of comparing the delta against the maximum, the code
compares the actual expiry against the maximum. Then instead of fixing the
delta to fit in, it sets the maximum delta as the expiry value.

This can result in various undesired outcomes, the worst possible one
being a timer expiring 15 days ahead to fire immediately.

Fixes: 500462a9de ("timers: Switch to a non-cascading wheel")
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20200717140551.29076-2-frederic@kernel.org
This commit is contained in:
Frederic Weisbecker 2020-07-17 16:05:40 +02:00 committed by Thomas Gleixner
parent 30c66fc30e
commit e2a71bdea8
1 changed files with 2 additions and 2 deletions
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4
kernel/time/timer.c
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@ -521,8 +521,8 @@ static int calc_wheel_index(unsigned long expires, unsigned long clk)
* Force expire obscene large timeouts to expire at the
* capacity limit of the wheel.
*/
if (expires >= WHEEL_TIMEOUT_CUTOFF)
expires = WHEEL_TIMEOUT_MAX;
if (delta >= WHEEL_TIMEOUT_CUTOFF)
expires = clk + WHEEL_TIMEOUT_MAX;
idx = calc_index(expires, LVL_DEPTH - 1);
}