tty: Don't block on IO when ldisc change is pending
[ Upstream commit c96cf923a98d1b094df9f0cf97a83e118817e31b ]
There might be situations where tty_ldisc_lock() has blocked, but there
is already IO on tty and it prevents line discipline changes.
It might theoretically turn into dead-lock.
Basically, provide more priority to pending tty_ldisc_lock() than to
servicing reads/writes over tty.
User-visible issue was reported by Mikulas where on pa-risc with
Debian 5 reboot took either 80 seconds, 3 minutes or 3:25 after proper
locking in tty_reopen().
Cc: Jiri Slaby <jslaby@suse.com>
Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
diff --git a/drivers/tty/n_r3964.c b/drivers/tty/n_r3964.c
index 3451114..ee0e07b 100644
--- a/drivers/tty/n_r3964.c
+++ b/drivers/tty/n_r3964.c
@@ -1080,7 +1080,7 @@
pMsg = remove_msg(pInfo, pClient);
if (pMsg == NULL) {
/* no messages available. */
- if (file->f_flags & O_NONBLOCK) {
+ if (tty_io_nonblock(tty, file)) {
ret = -EAGAIN;
goto unlock;
}