A deadlock can be initiated by userspace via ioctl(SNDCTL_SEQ_OUTOFBAND)
on /dev/sequencer with TMR_ECHO midi event.
In this case the control flow is:
sound_ioctl()
-> case SND_DEV_SEQ:
case SND_DEV_SEQ2:
sequencer_ioctl()
-> case SNDCTL_SEQ_OUTOFBAND:
spin_lock_irqsave(&lock,flags);
play_event();
-> case EV_TIMING:
seq_timing_event()
-> case TMR_ECHO:
seq_copy_to_input()
-> spin_lock_irqsave(&lock,flags);
It seems that spin_lock_irqsave() around play_event() is not necessary,
because the only other call location in seq_startplay() makes the call
without acquiring spinlock.
So, the patch just removes spinlocks around play_event().
By the way, it removes unreachable code in seq_timing_event(),
since (seq_mode == SEQ_2) case is handled in the beginning.
Compile tested only.
Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
The modular sound driver patches were funded by Red Hat Software
(www.redhat.com). The sound driver here is thus a modified version of
Hannu's code. Please bear that in mind when considering the appropriate
forums for bug reporting.
Alan Cox
bc26d4d06e