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authorPeter Hurley <peter@hurleysoftware.com>2013-03-06 07:20:57 -0500
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-03-15 14:02:33 -0700
commit25fdf2435139542759df2eeb59e4998923c13403 (patch)
tree8ae08d45b06959acbcb0dca62f59e322af0322d3
parentf91e2590410bd992e3f065d17c55329bdaa51b1d (diff)
tty: Signal SIGHUP before hanging up ldisc
An exiting session leader can hang if a foreground process is blocking for line discipline i/o, eg. in n_tty_read(). This happens because the blocking reader is holding an ldisc reference (indicating the line discipline is in-use) which prevents __tty_hangup() from recycling the line discipline. Although waiters are woken before attempting to gain exclusive access for changing the ldisc, the blocking reader in this case will not exit the i/o loop since it has not yet received SIGHUP (because it has not been sent). Instead, perform signalling first, then recycle the line discipline. Fixes: INFO: task init:1 blocked for more than 120 seconds. "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. init D 00000000001d7180 2688 1 0 0x00000002 ffff8800b9acfba8 0000000000000002 00000000001d7180 ffff8800b9b10048 ffff8800b94cb000 ffff8800b9b10000 00000000001d7180 00000000001d7180 ffff8800b9b10000 ffff8800b9acffd8 00000000001d7180 00000000001d7180 Call Trace: [<ffffffff83db9909>] __schedule+0x2e9/0x3b0 [<ffffffff83db9b35>] schedule+0x55/0x60 [<ffffffff83db74ba>] schedule_timeout+0x3a/0x370 [<ffffffff81182349>] ? mark_held_locks+0xf9/0x130 [<ffffffff83dbab38>] ? down_failed+0x108/0x200 [<ffffffff83dbb7ab>] ? _raw_spin_unlock_irq+0x2b/0x80 [<ffffffff81182608>] ? trace_hardirqs_on_caller+0x128/0x160 [<ffffffff83dbab61>] down_failed+0x131/0x200 [<ffffffff83dbbfad>] ? tty_ldisc_lock_pair_timeout+0xcd/0x120 [<ffffffff83dbae03>] ldsem_down_write+0xd3/0x113 [<ffffffff83dbbfad>] ? tty_ldisc_lock_pair_timeout+0xcd/0x120 [<ffffffff8118264d>] ? trace_hardirqs_on+0xd/0x10 [<ffffffff83dbbfad>] tty_ldisc_lock_pair_timeout+0xcd/0x120 [<ffffffff81c3df60>] tty_ldisc_hangup+0xd0/0x220 [<ffffffff81c35bd7>] __tty_hangup+0x137/0x4f0 [<ffffffff81c37c7c>] disassociate_ctty+0x6c/0x230 [<ffffffff8111290c>] do_exit+0x41c/0x590 [<ffffffff8107ad34>] ? syscall_trace_enter+0x24/0x2e0 [<ffffffff81112b4a>] do_group_exit+0x8a/0xc0 [<ffffffff81112b92>] sys_exit_group+0x12/0x20 [<ffffffff83dc49d8>] tracesys+0xe1/0xe6 1 lock held by init/1: #0: (&tty->ldisc_sem){++++++}, at: [<ffffffff83dbbfad>] tty_ldisc_lock_pair_timeout+0xcd/0x120 Reported-by: Sasha Levin <levinsasha928@gmail.com> Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Acked-by: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/tty/tty_io.c10
1 files changed, 5 insertions, 5 deletions
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 3feca406dc3..d3ddb31e363 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -651,17 +651,17 @@ static void __tty_hangup(struct tty_struct *tty, int exit_session)
}
spin_unlock(&tty_files_lock);
+ refs = tty_signal_session_leader(tty, exit_session);
+ /* Account for the p->signal references we killed */
+ while (refs--)
+ tty_kref_put(tty);
+
/*
* it drops BTM and thus races with reopen
* we protect the race by TTY_HUPPING
*/
tty_ldisc_hangup(tty);
- refs = tty_signal_session_leader(tty, exit_session);
- /* Account for the p->signal references we killed */
- while (refs--)
- tty_kref_put(tty);
-
spin_lock_irq(&tty->ctrl_lock);
clear_bit(TTY_THROTTLED, &tty->flags);
clear_bit(TTY_PUSH, &tty->flags);