linux-kernel - [tip: timers/urgent] timer: Fix wheel index calculation on last level

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Message-ID: <159501537091.4006.13327108405728570679.tip-bot2@tip-bot2>
Date:   Fri, 17 Jul 2020 19:49:30 -0000
From:   "tip-bot2 for Frederic Weisbecker" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, stable@...r.kernel.org,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: timers/urgent] timer: Fix wheel index calculation on last level

The following commit has been merged into the timers/urgent branch of tip:

Commit-ID:     e2a71bdea81690b6ef11f4368261ec6f5b6891aa
Gitweb:        https://git.kernel.org/tip/e2a71bdea81690b6ef11f4368261ec6f5b6891aa
Author:        Frederic Weisbecker <frederic@...nel.org>
AuthorDate:    Fri, 17 Jul 2020 16:05:40 +02:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Fri, 17 Jul 2020 21:44:05 +02:00

timer: Fix wheel index calculation on last level

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

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

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 9a838d3..df1ff80 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -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);
 	}