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From: Frederic Weisbecker <frederic@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>,
	Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	stable@vger.kernel.org
Subject: [PATCH 01/12] timer: Fix wheel index calculation on last level
Date: Fri, 17 Jul 2020 16:05:40 +0200	[thread overview]
Message-ID: <20200717140551.29076-2-frederic@kernel.org> (raw)
In-Reply-To: <20200717140551.29076-1-frederic@kernel.org>

When an expiration delta falls into the last level of the wheel, we want
to compare that delta against the maximum possible delay and reduce our
delta to fit in if necessary.

However instead of comparing the delta against the maximum, we are
comparing the actual expiry against the maximum. Then instead of fixing
the delta to fit in, we set 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@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.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 9a838d38dbe6..df1ff803acc4 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);
 	}
-- 
2.26.2


  reply	other threads:[~2020-07-17 14:06 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 14:05 [PATCH 00/11] timer: Reduce timers softirq v3 Frederic Weisbecker
2020-07-17 14:05 ` Frederic Weisbecker [this message]
2020-07-17 19:49   ` [tip: timers/urgent] timer: Fix wheel index calculation on last level tip-bot2 for Frederic Weisbecker
2020-07-17 14:05 ` [PATCH 02/12] timer: Preserve higher bits of expiration on index calculation Frederic Weisbecker
2020-07-17 20:00   ` [tip: timers/core] timers: " tip-bot2 for Frederic Weisbecker
2020-07-17 14:05 ` [PATCH 03/12] timers: Use only bucket expiry for base->next_expiry value Frederic Weisbecker
2020-07-17 20:00   ` [tip: timers/core] " tip-bot2 for Anna-Maria Behnsen
2020-07-17 14:05 ` [PATCH 04/12] timer: Move trigger_dyntick_cpu() to enqueue_timer() Frederic Weisbecker
2020-07-17 20:00   ` [tip: timers/core] timers: " tip-bot2 for Frederic Weisbecker
2020-07-17 14:05 ` [PATCH 05/12] timer: Add comments about calc_index() ceiling work Frederic Weisbecker
2020-07-17 20:00   ` [tip: timers/core] timers: " tip-bot2 for Frederic Weisbecker
2020-07-17 14:05 ` [PATCH 06/12] timer: Optimize _next_timer_interrupt() level iteration Frederic Weisbecker
2020-07-17 20:00   ` [tip: timers/core] timers: " tip-bot2 for Frederic Weisbecker
2020-07-17 14:05 ` [PATCH 07/12] timers: Always keep track of next expiry Frederic Weisbecker
2020-07-17 20:00   ` [tip: timers/core] " tip-bot2 for Frederic Weisbecker
2020-07-17 14:05 ` [PATCH 08/12] timer: Reuse next expiry cache after nohz exit Frederic Weisbecker
2020-07-17 20:00   ` [tip: timers/core] timers: " tip-bot2 for Frederic Weisbecker
2020-07-17 14:05 ` [PATCH 09/12] timer: Expand clk forward logic beyond nohz Frederic Weisbecker
2020-07-17 20:00   ` [tip: timers/core] timers: " tip-bot2 for Frederic Weisbecker
2020-07-17 14:05 ` [PATCH 10/12] timer: Spare timer softirq until next expiry Frederic Weisbecker
2020-07-17 20:00   ` [tip: timers/core] timers: " tip-bot2 for Frederic Weisbecker
2020-07-17 14:05 ` [PATCH 11/12] timer: Remove must_forward_clk Frederic Weisbecker
2020-07-17 20:00   ` [tip: timers/core] timers: " tip-bot2 for Frederic Weisbecker
2020-07-17 14:05 ` [PATCH 12/12] timer: Lower base clock forwarding threshold Frederic Weisbecker
2020-07-17 20:00   ` [tip: timers/core] timers: " tip-bot2 for Frederic Weisbecker

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