On 05/31/17 05:48, valdis.kletni...@vt.edu wrote:
Pretty drastic. Hit ^S to pause scrolling, and instantly hung terminal. Seen on both urxvt and xterm under x11, and on virtual console screens.This appears in dmesg: [ 1844.182058] INFO: task kworker/u8:3:129 blocked for more than 120 seconds. [ 1844.182073] Tainted: G OE 4.12.0-rc3-next-20170530 #489 [ 1844.182078] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 1844.182085] kworker/u8:3 D11008 129 2 0x00000000 [ 1844.182109] Workqueue: events_unbound flush_to_ldisc [ 1844.182118] Call Trace: [ 1844.182136] __schedule+0x43e/0x1020 [ 1844.182147] ? schedule_preempt_disabled+0x27/0xd0 [ 1844.182156] schedule+0x5d/0x1d0 [ 1844.182164] ? __mutex_lock+0x4c9/0x11c0 [ 1844.182172] schedule_preempt_disabled+0x27/0xd0 [ 1844.182179] __mutex_lock+0x4c9/0x11c0 [ 1844.182191] ? tty_port_default_receive_buf+0x58/0xc0 [ 1844.182204] ? ldsem_down_read_trylock+0xc3/0x130 [ 1844.182215] mutex_lock_nested+0x1b/0x20 [ 1844.182222] ? mutex_lock_nested+0x1b/0x20 [ 1844.182230] tty_port_default_receive_buf+0x58/0xc0 [ 1844.182240] flush_to_ldisc+0xea/0x220 [ 1844.182249] ? trace_hardirqs_on_caller+0x16/0x290 [ 1844.182262] process_one_work+0x3d6/0xd00 [ 1844.182269] ? lock_acquire+0xae/0x2f0 [ 1844.182284] worker_thread+0x71/0x830 [ 1844.182297] kthread+0x1a9/0x270 [ 1844.182304] ? process_one_work+0xd00/0xd00 [ 1844.182310] ? kthread_create_on_node+0x70/0x70 [ 1844.182321] ret_from_fork+0x27/0x40 [ 1844.182608] INFO: lockdep is turned off. Bisects down to this commit, and things work when it's reverted. Commit 925bb1ce47f4. Author: Vegard Nossum <vegard.nos...@oracle.com> Date: Thu May 11 12:18:52 2017 +0200 tty: fix port buffer locking tty_insert_flip_string_fixed_flag() is racy against itself when called from the ioctl(TCXONC, TCION/TCIOFF) path [1] and the flush_to_ldisc() workqueue path [2].
Gah, if it's that easy to trigger a deadlock (as opposed to just a lockdep warning), we should revert the patch until I have a better fix. ^S doesn't seem to reproduce it here, though. Too bad your stack trace doesn't show the process already holding the lock. Vegard
