Commit 6afbcf3c authored by Takashi Iwai's avatar Takashi Iwai Committed by Kamal Mostafa

ALSA: timer: Use mod_timer() for rearming the system timer

commit 4a07083e upstream.

ALSA system timer backend stops the timer via del_timer() without sync
and leaves del_timer_sync() at the close instead.  This is because of
the restriction by the design of ALSA timer: namely, the stop callback
may be called from the timer handler, and calling the sync shall lead
to a hangup.  However, this also triggers a kernel BUG() when the
timer is rearmed immediately after stopping without sync:
 kernel BUG at kernel/time/timer.c:966!
 Call Trace:
  <IRQ>
  [<ffffffff8239c94e>] snd_timer_s_start+0x13e/0x1a0
  [<ffffffff8239e1f4>] snd_timer_interrupt+0x504/0xec0
  [<ffffffff8122fca0>] ? debug_check_no_locks_freed+0x290/0x290
  [<ffffffff8239ec64>] snd_timer_s_function+0xb4/0x120
  [<ffffffff81296b72>] call_timer_fn+0x162/0x520
  [<ffffffff81296add>] ? call_timer_fn+0xcd/0x520
  [<ffffffff8239ebb0>] ? snd_timer_interrupt+0xec0/0xec0
  ....

It's the place where add_timer() checks the pending timer.  It's clear
that this may happen after the immediate restart without sync in our
cases.

So, the workaround here is just to use mod_timer() instead of
add_timer().  This looks like a band-aid fix, but it's a right move,
as snd_timer_interrupt() takes care of the continuous rearm of timer.
Reported-by: default avatarJiri Slaby <jslaby@suse.cz>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
Signed-off-by: default avatarKamal Mostafa <kamal@canonical.com>
parent 7d76cfd6
...@@ -1051,8 +1051,8 @@ static int snd_timer_s_start(struct snd_timer * timer) ...@@ -1051,8 +1051,8 @@ static int snd_timer_s_start(struct snd_timer * timer)
njiff += timer->sticks - priv->correction; njiff += timer->sticks - priv->correction;
priv->correction = 0; priv->correction = 0;
} }
priv->last_expires = priv->tlist.expires = njiff; priv->last_expires = njiff;
add_timer(&priv->tlist); mod_timer(&priv->tlist, njiff);
return 0; return 0;
} }
......
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