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authorArjan van de Ven <>2011-09-15 08:49:25 +0200
committerTakashi Iwai <>2011-09-15 09:03:16 +0200
commit763437a9e7737535b2fc72175ad4974048769be6 (patch)
tree53a1fdf8c411fda8678f3ffc73826d82b83c3e62 /MAINTAINERS
parent4038a12e7443b5fed3e526c475c38c115d9600f6 (diff)
ALSA: pcm - fix race condition in wait_for_avail()
wait_for_avail() in pcm_lib.c has a race in it (observed in practice by an Intel validation group). The function is supposed to return once space in the buffer has become available, or if some timeout happens. The entity that creates space (irq handler of sound driver and some such) will do a wake up on a waitqueue that this function registers for. However there are two races in the existing code 1) If space became available between the caller noticing there was no space and this function actually sleeping, the wakeup is missed and the timeout condition will happen instead 2) If a wakeup happened but not sufficient space became available, the code will loop again and wait for more space. However, if the second wake comes in prior to hitting the schedule_timeout_interruptible(), it will be missed, and potentially you'll wait out until the timeout happens. The fix consists of using more careful setting of the current state (so that if a wakeup happens in the main loop window, the schedule_timeout() falls through) and by checking for available space prior to going into the schedule_timeout() loop, but after being on the waitqueue and having the state set to interruptible. [tiwai: the following changes have been added to Arjan's original patch: - merged akpm's fix for waitqueue adding order into a single patch - reduction of duplicated code of avail check ] Signed-off-by: Arjan van de Ven <> Signed-off-by: Andrew Morton <> Cc: <> Signed-off-by: Takashi Iwai <>
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