Kosuke Tatsukawa 694470273d ALSA: seq_oss: fix waitqueue_active without memory barrier in snd-seq-oss ... 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>		2015-10-09 09:45:52 +02:00
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oss	ALSA: seq_oss: fix waitqueue_active without memory barrier in snd-seq-oss	2015-10-09 09:45:52 +02:00
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