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snd_seq_oss_readq_put_event() seems to be missing a memory barrier which
might cause the waker to not notice the waiter and miss sending a
wake_up as in the following figure.
snd_seq_oss_readq_put_event snd_seq_oss_readq_wait
------------------------------------------------------------------------
/* wait_event_interruptible_timeout */
/* __wait_event_interruptible_timeout */
/* ___wait_event */
for (;;) { prepare_to_wait_event(&wq, &__wait,
state);
spin_lock_irqsave(&q->lock, flags);
if (waitqueue_active(&q->midi_sleep))
/* The CPU might reorder the test for
the waitqueue up here, before
prior writes complete */
if ((q->qlen>0 || q->head==q->tail)
...
__ret = schedule_timeout(__ret)
if (q->qlen >= q->maxlen - 1) {
memcpy(&q->q[q->tail], ev, sizeof(*ev));
q->tail = (q->tail + 1) % q->maxlen;
q->qlen++;
------------------------------------------------------------------------
There are two other place in sound/core/seq/oss/ which have similar
code. The attached patch removes the call to waitqueue_active() leaving
just wake_up() behind. This fixes the problem because the call to
spin_lock_irqsave() in wake_up() will be an ACQUIRE operation.
I found this issue when I was looking through the linux source code
for places calling waitqueue_active() before wake_up*(), but without
preceding memory barriers, after sending a patch to fix a similar
issue in drivers/tty/n_tty.c (Details about the original issue can be
found here: https://lkml.org/lkml/2015/9/28/849).
Signed-off-by: Kosuke Tatsukawa <tatsu@ab.jp.nec.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
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|---|---|---|
| .. | ||
| oss | ||
| Kconfig | ||
| Makefile | ||
| seq_clientmgr.c | ||
| seq_clientmgr.h | ||
| seq_compat.c | ||
| seq_device.c | ||
| seq_dummy.c | ||
| seq_fifo.c | ||
| seq_fifo.h | ||
| seq_info.c | ||
| seq_info.h | ||
| seq_lock.c | ||
| seq_lock.h | ||
| seq_memory.c | ||
| seq_memory.h | ||
| seq_midi_emul.c | ||
| seq_midi_event.c | ||
| seq_midi.c | ||
| seq_ports.c | ||
| seq_ports.h | ||
| seq_prioq.c | ||
| seq_prioq.h | ||
| seq_queue.c | ||
| seq_queue.h | ||
| seq_system.c | ||
| seq_system.h | ||
| seq_timer.c | ||
| seq_timer.h | ||
| seq_virmidi.c | ||
| seq.c | ||