From: Kalle Kankare <kalle.kankare@vincit.fi>
To: linux-kernel@vger.kernel.org
Cc: Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>
Subject: During high load wait_event_timeout might return a wrong value
Date: Tue, 10 Nov 2015 09:18:12 +0200 [thread overview]
Message-ID: <20151110091812.1e7f326e@kalleka-typewriter> (raw)
Hi,
The problem is that the call to might_sleep might sleep and the return value of wait_event_timeout does not account for the time slept in there.
The might_sleep includes a call to __schedule if CONFIG_PREEMPT_VOLUNTARY is defined.
A problematic scenario can be like the following:
- A driver calls wait_event_timeout with timeout = 10 jiffies, starts sleeping in might_sleep.
- An interrupt handler sets the condition true at 5 jiffies and calls wake_up for the waitqueue.
- Due to high load the might_sleep wakes up at 100 jiffies.
- In the next if the __wait_cond_timeout returns 1 without manipulating __ret.
- wait_event_timeout returns 10 where it should have returned 1 to denote that a timeout was reached.
Or am I misunderstanding what the return value should be ?
next reply other threads:[~2015-11-10 7:19 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-10 7:18 Kalle Kankare [this message]
2015-11-10 11:09 ` Peter Zijlstra
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