Path: csiph.com!aioe.org!bofh.it!news.nic.it!robomod From: Willy Tarreau Newsgroups: linux.kernel Subject: [PATCH 2.6.32 32/55] ALSA: hrtimer: Fix stall by hrtimer_cancel() Date: Fri, 04 Mar 2016 17:20:01 +0100 Message-ID: References: X-Original-To: linux-kernel@vger.kernel.org, stable@vger.kernel.org User-Agent: quilt/0.63-1 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 57 Organization: linux.* mail to news gateway X-Original-Cc: Takashi Iwai , Ben Hutchings , Willy Tarreau X-Original-Date: Fri, 04 Mar 2016 16:30:32 +0100 X-Original-Message-ID: <20160304153002.107916314@1wt.eu> X-Original-References: <148ee355b419e9976ca727513a1405c8@local> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1350374 2.6.32-longterm review patch. If anyone has any objections, please let me know. ------------------ From: Takashi Iwai commit 2ba1fe7a06d3624f9a7586d672b55f08f7c670f3 upstream. hrtimer_cancel() waits for the completion from the callback, thus it must not be called inside the callback itself. This was already a problem in the past with ALSA hrtimer driver, and the early commit [fcfdebe70759: ALSA: hrtimer - Fix lock-up] tried to address it. However, the previous fix is still insufficient: it may still cause a lockup when the ALSA timer instance reprograms itself in its callback. Then it invokes the start function even in snd_timer_interrupt() that is called in hrtimer callback itself, results in a CPU stall. This is no hypothetical problem but actually triggered by syzkaller fuzzer. This patch tries to fix the issue again. Now we call hrtimer_try_to_cancel() at both start and stop functions so that it won't fall into a deadlock, yet giving some chance to cancel the queue if the functions have been called outside the callback. The proper hrtimer_cancel() is called in anyway at closing, so this should be enough. Reported-and-tested-by: Dmitry Vyukov Signed-off-by: Takashi Iwai Signed-off-by: Ben Hutchings Signed-off-by: Willy Tarreau --- sound/core/hrtimer.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/sound/core/hrtimer.c b/sound/core/hrtimer.c index 2475bda..cbccaf2 100644 --- a/sound/core/hrtimer.c +++ b/sound/core/hrtimer.c @@ -89,7 +89,7 @@ static int snd_hrtimer_start(struct snd_timer *t) struct snd_hrtimer *stime = t->private_data; atomic_set(&stime->running, 0); - hrtimer_cancel(&stime->hrt); + hrtimer_try_to_cancel(&stime->hrt); hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution), HRTIMER_MODE_REL); atomic_set(&stime->running, 1); @@ -100,6 +100,7 @@ static int snd_hrtimer_stop(struct snd_timer *t) { struct snd_hrtimer *stime = t->private_data; atomic_set(&stime->running, 0); + hrtimer_try_to_cancel(&stime->hrt); return 0; } -- 1.7.12.2.21.g234cd45.dirty