From 25fdf2435139542759df2eeb59e4998923c13403 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Wed, 6 Mar 2013 07:20:57 -0500 Subject: [PATCH] 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: [] __schedule+0x2e9/0x3b0 [] schedule+0x55/0x60 [] schedule_timeout+0x3a/0x370 [] ? mark_held_locks+0xf9/0x130 [] ? down_failed+0x108/0x200 [] ? _raw_spin_unlock_irq+0x2b/0x80 [] ? trace_hardirqs_on_caller+0x128/0x160 [] down_failed+0x131/0x200 [] ? tty_ldisc_lock_pair_timeout+0xcd/0x120 [] ldsem_down_write+0xd3/0x113 [] ? tty_ldisc_lock_pair_timeout+0xcd/0x120 [] ? trace_hardirqs_on+0xd/0x10 [] tty_ldisc_lock_pair_timeout+0xcd/0x120 [] tty_ldisc_hangup+0xd0/0x220 [] __tty_hangup+0x137/0x4f0 [] disassociate_ctty+0x6c/0x230 [] do_exit+0x41c/0x590 [] ? syscall_trace_enter+0x24/0x2e0 [] do_group_exit+0x8a/0xc0 [] sys_exit_group+0x12/0x20 [] tracesys+0xe1/0xe6 1 lock held by init/1: #0: (&tty->ldisc_sem){++++++}, at: [] tty_ldisc_lock_pair_timeout+0xcd/0x120 Reported-by: Sasha Levin Signed-off-by: Peter Hurley Acked-by: Jiri Slaby Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_io.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 3feca406dc36..d3ddb31e363e 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); -- 2.20.1