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55 lines
2.0 KiB
Diff
55 lines
2.0 KiB
Diff
From 2ba1fe7a06d3624f9a7586d672b55f08f7c670f3 Mon Sep 17 00:00:00 2001
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From: Takashi Iwai <tiwai@suse.de>
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Date: Mon, 18 Jan 2016 13:52:47 +0100
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Subject: ALSA: hrtimer: Fix stall by hrtimer_cancel()
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hrtimer_cancel() waits for the completion from the callback, thus it
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must not be called inside the callback itself. This was already a
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problem in the past with ALSA hrtimer driver, and the early commit
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[fcfdebe70759: ALSA: hrtimer - Fix lock-up] tried to address it.
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However, the previous fix is still insufficient: it may still cause a
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lockup when the ALSA timer instance reprograms itself in its callback.
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Then it invokes the start function even in snd_timer_interrupt() that
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is called in hrtimer callback itself, results in a CPU stall. This is
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no hypothetical problem but actually triggered by syzkaller fuzzer.
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This patch tries to fix the issue again. Now we call
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hrtimer_try_to_cancel() at both start and stop functions so that it
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won't fall into a deadlock, yet giving some chance to cancel the queue
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if the functions have been called outside the callback. The proper
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hrtimer_cancel() is called in anyway at closing, so this should be
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enough.
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Reported-and-tested-by: Dmitry Vyukov <dvyukov@google.com>
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Cc: <stable@vger.kernel.org>
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Signed-off-by: Takashi Iwai <tiwai@suse.de>
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---
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sound/core/hrtimer.c | 3 ++-
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1 file changed, 2 insertions(+), 1 deletion(-)
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diff --git a/sound/core/hrtimer.c b/sound/core/hrtimer.c
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index f845ecf..656d9a9 100644
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--- a/sound/core/hrtimer.c
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+++ b/sound/core/hrtimer.c
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@@ -90,7 +90,7 @@ static int snd_hrtimer_start(struct snd_timer *t)
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struct snd_hrtimer *stime = t->private_data;
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atomic_set(&stime->running, 0);
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- hrtimer_cancel(&stime->hrt);
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+ hrtimer_try_to_cancel(&stime->hrt);
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hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution),
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HRTIMER_MODE_REL);
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atomic_set(&stime->running, 1);
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@@ -101,6 +101,7 @@ static int snd_hrtimer_stop(struct snd_timer *t)
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{
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struct snd_hrtimer *stime = t->private_data;
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atomic_set(&stime->running, 0);
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+ hrtimer_try_to_cancel(&stime->hrt);
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return 0;
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}
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--
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cgit v1.1
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