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Date: Sat, 22 Sep 2012 10:35:46 +0200
From: Sasha Levin <levinsasha928@...il.com>
To: Jiri Slaby <jslaby@...e.cz>
CC: Shachar Shemesh <shachar@...eu.tv>, Greg KH <greg@...ah.com>,
LKML <linux-kernel@...r.kernel.org>, kzak@...hat.com,
Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] tty ldisc: Close/Reopen race prevention should check
the proper flag
On 09/19/2012 09:25 PM, Jiri Slaby wrote:
> On 07/10/2012 06:54 AM, Shachar Shemesh wrote:
>> > From: Shachar Shemesh <shachar@...eu.tv>
>> >
>> > Commit acfa747b introduced the TTY_HUPPING flag to distinguish
>> > closed TTY from currently closing ones. The test in tty_set_ldisc
>> > still remained pointing at the old flag. This causes pppd to
>> > sometimes lapse into uninterruptible sleep when killed and
>> > restarted.
>> >
>> > Signed-off-by: Shachar Shemesh <shachar@...eu.tv>
>> > ---
>> > Tested with 3.2.20 kernel.
>> >
>> > diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
>> > index 24b95db..a662a24 100644
>> > --- a/drivers/tty/tty_ldisc.c
>> > +++ b/drivers/tty/tty_ldisc.c
>> > @@ -658,7 +658,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
>> > goto enable;
>> > }
>> >
>> > - if (test_bit(TTY_HUPPED, &tty->flags)) {
>> > + if (test_bit(TTY_HUPPING, &tty->flags)) {
>> > /* We were raced by the hangup method. It will have stomped
>> > the ldisc data and closed the ldisc down */
>> > clear_bit(TTY_LDISC_CHANGING, &tty->flags);
> Yes, that makes the issue go away, but does not seem to be right too.
> There are two issues I see:
> * TTY_HUPPED has no use now. That is incorrect. Here should be a test
> for both flags, I think.
> * The change forces the set_ldisc path to always re-open the ldisc even
> if it the terminal is HUPPED.
This patch also causes hangs on newer kernels. Can it be reverted please?
[ 482.860279] INFO: task init:1 blocked for more than 120 seconds.
[ 482.864244] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
message.
[ 482.867175] init D ffff88000d618000 3424 1 0 0x00000002
[ 482.869321] ffff88000d5b9c28 0000000000000002 ffff88000d5b9be8 ffffffff8114ff65
[ 482.870387] ffff88000d5b9fd8 ffff88000d5b9fd8 ffff88000d5b9fd8 ffff88000d5b9fd8
[ 482.871419] ffff88000d618000 ffff88000d5b0000 ffff88000d5b08f0 7fffffffffffffff
[ 482.872143] Call Trace:
[ 482.872336] [<ffffffff8114ff65>] ? sched_clock_local+0x25/0xa0
[ 482.872796] [<ffffffff839edb35>] schedule+0x55/0x60
[ 482.873433] [<ffffffff839ebab5>] schedule_timeout+0x45/0x360
[ 482.874134] [<ffffffff839ef25d>] ? _raw_spin_unlock_irqrestore+0x5d/0xb0
[ 482.874752] [<ffffffff8117a5dd>] ? trace_hardirqs_on+0xd/0x10
[ 482.875835] [<ffffffff839ef284>] ? _raw_spin_unlock_irqrestore+0x84/0xb0
[ 482.876744] [<ffffffff81136f97>] ? prepare_to_wait+0x77/0x90
[ 482.877485] [<ffffffff81b98ef6>] tty_ldisc_wait_idle.isra.7+0x76/0xb0
[ 482.878428] [<ffffffff81137170>] ? abort_exclusive_wait+0xb0/0xb0
[ 482.879239] [<ffffffff81b99bab>] tty_ldisc_hangup+0x1cb/0x320
[ 482.879988] [<ffffffff81b90d52>] ? __tty_hangup+0x122/0x430
[ 482.880491] [<ffffffff81b90d5a>] __tty_hangup+0x12a/0x430
[ 482.880904] [<ffffffff839ef284>] ? _raw_spin_unlock_irqrestore+0x84/0xb0
[ 482.881406] [<ffffffff81b931fc>] disassociate_ctty+0x6c/0x230
[ 482.882141] [<ffffffff8110dc98>] do_exit+0x3d8/0xa90
[ 482.882803] [<ffffffff8117a5dd>] ? trace_hardirqs_on+0xd/0x10
[ 482.883564] [<ffffffff8110e414>] do_group_exit+0x84/0xd0
[ 482.884261] [<ffffffff8110e472>] sys_exit_group+0x12/0x20
[ 482.884975] [<ffffffff839f0ce8>] tracesys+0xe1/0xe6
[ 482.885618] 1 lock held by init/1:
[ 482.886059] #0: (&tty->ldisc_mutex){+.+.+.}, at: [<ffffffff81b99b02>]
tty_ldisc_hangup+0x122/0x320
[ 482.941519] rcu-torture: rtc: ffffffff8647dc30 ver: 746 tfle: 0 rta: 746
rtaf: 0 rtf: 745 rtmbe: 0 rtbke: 0 rtbre: 0 rtbf: 0 rtb: 0 nt: 5116 onoff:
0/0:0/0 -1,0:-1,0 0:0 (HZ=100) barrier: 0/0:0
[ 482.941519] rcu-torture: Reader Pipe: 664658 22 0 0 0 0 0 0 0 0 0
[ 482.941519] rcu-torture: Reader Batch: 664669 11 0 0 0 0 0 0 0 0 0
[ 482.941519] rcu-torture: Free-Block Circulation: 745 745 745 745 745 745 745
745 745 745 0
[ 542.942392] rcu-torture: rtc: ffffffff8647dc30 ver: 746 tfle: 0 rta: 746
rtaf: 0 rtf: 745 rtmbe: 0 rtbke: 0 rtbre: 0 rtbf: 0 rtb: 0 nt: 5116 onoff:
0/0:0/0 -1,0:-1,0 0:0 (HZ=100) barrier: 0/0:0
[ 542.942392] rcu-torture: Reader Pipe: 664658 22 0 0 0 0 0 0 0 0 0
[ 542.942392] rcu-torture: Reader Batch: 664669 11 0 0 0 0 0 0 0 0 0
[ 542.942392] rcu-torture: Free-Block Circulation: 745 745 745 745 745 745 745
745 745 745 0
[ 547.040453] kworker/u:3 (4274) used greatest stack depth: 3200 bytes left
[ 602.880374] INFO: task init:1 blocked for more than 120 seconds.
[ 602.883834] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
message.
[ 602.886219] init D ffff88000d618000 3424 1 0 0x00000002
[ 602.887347] ffff88000d5b9c28 0000000000000002 ffff88000d5b9be8 ffffffff8114ff65
[ 602.888383] ffff88000d5b9fd8 ffff88000d5b9fd8 ffff88000d5b9fd8 ffff88000d5b9fd8
[ 602.889554] ffff88000d618000 ffff88000d5b0000 ffff88000d5b08f0 7fffffffffffffff
[ 602.890851] Call Trace:
[ 602.891240] [<ffffffff8114ff65>] ? sched_clock_local+0x25/0xa0
[ 602.892128] [<ffffffff839edb35>] schedule+0x55/0x60
[ 602.892902] [<ffffffff839ebab5>] schedule_timeout+0x45/0x360
[ 602.893738] [<ffffffff839ef25d>] ? _raw_spin_unlock_irqrestore+0x5d/0xb0
[ 602.894713] [<ffffffff8117a5dd>] ? trace_hardirqs_on+0xd/0x10
[ 602.895656] [<ffffffff839ef284>] ? _raw_spin_unlock_irqrestore+0x84/0xb0
[ 602.896680] [<ffffffff81136f97>] ? prepare_to_wait+0x77/0x90
[ 602.897557] [<ffffffff81b98ef6>] tty_ldisc_wait_idle.isra.7+0x76/0xb0
[ 602.898509] [<ffffffff81137170>] ? abort_exclusive_wait+0xb0/0xb0
[ 602.899415] [<ffffffff81b99bab>] tty_ldisc_hangup+0x1cb/0x320
[ 602.900363] [<ffffffff81b90d52>] ? __tty_hangup+0x122/0x430
[ 602.901241] [<ffffffff81b90d5a>] __tty_hangup+0x12a/0x430
[ 602.902052] [<ffffffff839ef284>] ? _raw_spin_unlock_irqrestore+0x84/0xb0
[ 602.903020] [<ffffffff81b931fc>] disassociate_ctty+0x6c/0x230
[ 602.903848] [<ffffffff8110dc98>] do_exit+0x3d8/0xa90
[ 602.904642] [<ffffffff8117a5dd>] ? trace_hardirqs_on+0xd/0x10
[ 602.905518] [<ffffffff8110e414>] do_group_exit+0x84/0xd0
[ 602.906427] [<ffffffff8110e472>] sys_exit_group+0x12/0x20
[ 602.907449] [<ffffffff839f0ce8>] tracesys+0xe1/0xe6
[ 602.908579] 1 lock held by init/1:
[ 602.909293] #0: (&tty->ldisc_mutex){+.+.+.}, at: [<ffffffff81b99b02>]
tty_ldisc_hangup+0x122/0x320
--
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