BugLink: https://bugs.launchpad.net/bugs/1792340

commit 50e9ffb1 upstream.

The virmidi output trigger tries to parse the all available bytes and
process sequencer events as much as possible.  In a normal situation,
this is supposed to be relatively short, but a program may give a huge
buffer and it'll take a long time in a single spin lock, which may
eventually lead to a soft lockup.

This patch simply adds a workaround, a cond_resched() call in the loop
if applicable.  A better solution would be to move the event processor
into a work, but let's put a duct-tape quickly at first.
Reported-and-tested-by: Dae R. Jeong <threeearcat@gmail.com>
Reported-by: syzbot+619d9f40141d826b097e@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>