linux-kernel - [PATCH 4.9 78/86] timer: Fix wheel index calculation on last level

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Message-Id: <20200720152757.164109862@linuxfoundation.org>
Date:   Mon, 20 Jul 2020 17:37:14 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Frederic Weisbecker <frederic@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 4.9 78/86] timer: Fix wheel index calculation on last level

From: Frederic Weisbecker <frederic@...nel.org>

commit e2a71bdea81690b6ef11f4368261ec6f5b6891aa upstream.

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: 500462a9de65 ("timers: Switch to a non-cascading wheel")
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/20200717140551.29076-2-frederic@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/time/timer.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -500,8 +500,8 @@ static int calc_wheel_index(unsigned lon
 		 * 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);
 	}