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[PATCH 3.2 61/87] ALSA: hrtimer: Fix stall by hrtimer_cancel()

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3.2.77-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@suse.de>

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 <dvyukov@google.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 sound/core/hrtimer.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/sound/core/hrtimer.c
+++ b/sound/core/hrtimer.c
@@ -90,7 +90,7 @@ static int snd_hrtimer_start(struct snd_
 	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);
@@ -101,6 +101,7 @@ static int snd_hrtimer_stop(struct snd_t
 {
 	struct snd_hrtimer *stime = t->private_data;
 	atomic_set(&stime->running, 0);
+	hrtimer_try_to_cancel(&stime->hrt);
 	return 0;
 }
 

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[PATCH 3.2 00/87] 3.2.77-rc1 review Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:20 +0100
  [PATCH 3.2 79/87] crypto: af_alg - Forbid bind(2) when nokey  child sockets are present Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:20 +0100
  [PATCH 3.2 17/87] asix: silence log message from oversize packet Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:20 +0100
  [PATCH 3.2 73/87] crypto: algif_hash - Require setkey before  accept(2) Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:20 +0100
  [PATCH 3.2 18/87] futex: Drop refcount if requeue_pi() acquired  the rtmutex Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:20 +0100
  [PATCH 3.2 60/87] crypto: af_alg - Fix socket double-free when  accept fails Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:20 +0100
  [PATCH 3.2 72/87] crypto: hash - Add crypto_ahash_has_setkey Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:20 +0100
  [PATCH 3.2 70/87] crypto: af_alg - Add nokey compatibility path Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:20 +0100
  [PATCH 3.2 57/87] ALSA: timer: Harden slave timer list handling Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:20 +0100
  [PATCH 3.2 61/87] ALSA: hrtimer: Fix stall by hrtimer_cancel() Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:20 +0100
  [PATCH 3.2 82/87] crypto: algif_skcipher - Load TX SG list after  waiting Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:20 +0100
  [PATCH 3.2 11/87] rtlwifi: fix memory leak for USB device Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:20 +0100
  [PATCH 3.2 64/87] ALSA: control: Avoid kernel warnings from tlv  ioctl with numid 0 Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:20 +0100
  [PATCH 3.2 01/87] [media] gspca: ov534/topro: prevent a division by 0 Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:20 +0100
  [PATCH 3.2 08/87] mtd: nand: fix ONFI parameter page layout Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 80/87] crypto: algif_hash - Fix race condition in  hash_check_key Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 04/87] SCSI: initio: remove duplicate module device table Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 87/87] [media] usbvision: fix crash on detecting  device with invalid configuration Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 15/87] powerpc: Make value-returning atomics fully ordered Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 10/87] xhci: refuse loading if nousb is used Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 05/87] KVM: x86: expose MSR_TSC_AUX to userspace Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 86/87] [media] usbvision fix overflow of interfaces array Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 85/87] [media] usbvision: fix leak of usb_dev on  failure paths in  usbvision_probe() Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 07/87] ath9k_htc: check for underflow in  ath9k_htc_rx_msg() Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 13/87] wlcore/wl12xx: spi: fix oops on firmware load Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 14/87] EDAC: Robustify workqueues destruction Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 19/87] ALSA: fm801: propagate TUNER_ONLY bit when  autodetected Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 84/87] [media] usbvision-video: fix memory leak of  alt_max_pkt_size Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 12/87] wlcore: SPI - fix spi transfer_list Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 16/87] powerpc: Make {cmp}xchg* and their atomic_  versions fully ordered Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 78/87] crypto: algif_skcipher - Remove custom release  parent function Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  [PATCH 3.2 03/87] [media] rc: allow rc modules to be loaded if  rc-main is not a module Ben Hutchings <ben@decadent.org.uk> - 2016-02-09 01:30 +0100
  Re: [PATCH 3.2 00/87] 3.2.77-rc1 review Guenter Roeck <linux@roeck-us.net> - 2016-02-09 05:00 +0100
    Re: [PATCH 3.2 00/87] 3.2.77-rc1 review Ben Hutchings <ben@decadent.org.uk> - 2016-02-10 02:10 +0100

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