Corey Wright wrote:
> On Fri, 30 Oct 2015 22:07:24 -0400
> Sasha Levin <sasha.levin@xxxxxxxxxx> wrote:
>
>> On 10/30/2015 09:56 PM, Corey Wright wrote:
>> > Running applications under GNU Screen causes the 3.18.23 kernel to stall and
>> > the application to hang. Reverting commit af32cc7b, ie "tty: fix stall caused
>> > by missing memory barrier in drivers/tty/n_tty.c", fixes the problem.
>>
>> Hi Corey,
>>
>> Does doing the same on mainline work for you?
>
> is 4.1.12 close enough (which i already had "on-hand")?
>
> it contains a similar commit 614ea4ea and tests successfully (ie no bug).
>
> so the problem appears to be limited to 3.18.23.
>
> thanks for getting me looking at and comparing the two versions!
>
> in 3.18.23 we add a spin_unlock_irqrestore inside the "if (tty->link->packet)"
> block, but we already have one outside of the if block.
>
> i'm thinking it accidentally got dragged along when porting the commit from
> 4.1 to 3.18 (because the one that was added in 3.18.23 is in the same location
> as the one already in 4.1).
>
> the below patch fixes the problem and passes the
> apt-and-lxc-start-run-under-screen-without-causing-a-stall test.
Thank you.
The original upstream patch just removes the
if (waitqueue_active(...))
line, so the spin_unlock_irqrestore() added in commit af32cc7b is extra
and should be removed.
> ---------- >8 ----- cut here ----- 8< ----------
> Remove extraneous, unmatched spin_unlock_irqrestore() introduced by commit
> af32cc7b.
>
> This prevents stalls when running command-line applications under GNU Screen.
>
> Fixes: af32cc7bde63 ("tty: fix stall caused by missing memory barrier in drivers/tty/n_tty.c")
> Signed-off-by: Corey Wright <undefined@xxxxxxxxx>
>
> --- linux-3.18.23~/drivers/tty/n_tty.c 2015-10-30 23:46:48.000000000 -0500
> +++ linux-3.18.23/drivers/tty/n_tty.c 2015-10-30 23:46:53.821376173 -0500
> @@ -364,7 +364,6 @@ static void n_tty_packet_mode_flush(stru
> spin_lock_irqsave(&tty->ctrl_lock, flags);
> if (tty->link->packet) {
> tty->ctrl_status |= TIOCPKT_FLUSHREAD;
> - spin_unlock_irqrestore(&tty->ctrl_lock, flags);
> wake_up_interruptible(&tty->link->read_wait);
> }
> spin_unlock_irqrestore(&tty->ctrl_lock, flags);
> ---------- >8 ----- cut here ----- 8< ----------
>
>> Thanks,
>> Sasha
>
> thank you!
>
> corey
> --
> undefined@xxxxxxxxx
---
Kosuke TATSUKAWA | 3rd IT Platform Department
| IT Platform Division, NEC Corporation
| tatsu@xxxxxxxxxxxxx
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