| From | Ben Hutchings <> | Date | Sat, 13 Aug 2016 18:42:51 +0100 | Subject | [PATCH 3.16 266/305] ALSA: timer: Fix negative queue usage by racy accesses |
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3.16.37-rc1 review patch. If anyone has any objections, please let me know.
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From: Takashi Iwai <tiwai@suse.de>
commit 3fa6993fef634e05d200d141a85df0b044572364 upstream.
The user timer tu->qused counter may go to a negative value when multiple concurrent reads are performed since both the check and the decrement of tu->qused are done in two individual locked contexts. This results in bogus read outs, and the endless loop in the user-space side.
The fix is to move the decrement of the tu->qused counter into the same spinlock context as the zero-check of the counter.
Signed-off-by: Takashi Iwai <tiwai@suse.de> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- sound/core/timer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -1965,6 +1965,7 @@ static ssize_t snd_timer_user_read(struc qhead = tu->qhead++; tu->qhead %= tu->queue_size; + tu->qused--; spin_unlock_irq(&tu->qlock); if (tu->tread) { @@ -1978,7 +1979,6 @@ static ssize_t snd_timer_user_read(struc } spin_lock_irq(&tu->qlock); - tu->qused--; if (err < 0) goto _error; result += unit;
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