On Sat, 31 Oct 2015 09:02:52 -0400
Sasha Levin <sasha.levin@xxxxxxxxxx> wrote:
> On 10/31/2015 01:37 AM, 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.
> >
> > ---------- >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);
>
> Hey Corey,
>
> Thanks for looking into it!
>
> I've pushed a corrected backport to the stable queue, if you could please confirm
> that it works for you I'll ship it as 3.18.24.
>
> The tree is available at git://git.kernel.org/pub/scm/linux/kernel/git/sashal/linux-stable.git linux-3.18.y-queue
i've successfully tested git branch linux-3.18.y-queue (git describe
v3.18.23-2-gb008351) with the revert and the repatch (commits 80e5c4dd and
b008351f, respectively). running apt-get and lxc-start under screen does not
cause a kernel stall.
> Thanks again!
thank you for maintaining 3.18!
corey
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undefined@xxxxxxxxx
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