Bug 13813

Summary:	Hangups in n_tty_read()
Product:	Drivers	Reporter:	Rafael J. Wysocki (rjw)
Component:	Other	Assignee:	drivers_other
Status:	CLOSED CODE_FIX
Severity:	normal
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	2.6.31-rc	Subsystem:
Regression:	Yes	Bisected commit-id:
Bug Depends on:
Bug Blocks:	13615

Description Rafael J. Wysocki 2009-07-22 20:53:24 UTC

Subject    : Hangups in n_tty_read()
Submitter  : Johannes Weiner <hannes@cmpxchg.org>
Date       : 2009-07-16 18:48
References : http://marc.info/?l=linux-kernel&m=124777019920579&w=4
Notify-Also : Alan Cox <alan@lxorguk.ukuu.org.uk>

This entry is being used for tracking a regression from 2.6.30.  Please don't
close it until the problem is fixed in the mainline.

Comment 1 Rafael J. Wysocki 2009-08-03 15:19:10 UTC

On Monday 03 August 2009, Johannes Weiner wrote:
> On Mon, Aug 03, 2009 at 03:15:10AM +0200, Frédéric Weisbecker wrote:
> > 2009/8/2 Rafael J. Wysocki <rjw@sisk.pl>:
> > > This message has been generated automatically as a part of a report
> > > of recent regressions.
> > >
> > > The following bug entry is on the current list of known regressions
> > > from 2.6.30.  Please verify if it still should be listed and let me know
> > > (either way).
> > >
> > >
> > > Bug-Entry       : http://bugzilla.kernel.org/show_bug.cgi?id=13813
> > > Subject         : Hangups in n_tty_read()
> > > Submitter       : Johannes Weiner <hannes@cmpxchg.org>
> > > Date            : 2009-07-16 18:48 (18 days old)
> > > References      : http://marc.info/?l=linux-kernel&m=124777019920579&w=4
> > 
> > 
> > Johannes,
> > 
> > Does it still happen with latest mainline?
> > Also, could you send us your .config ?
> 
> I wanted to wait until confirming this as this bug could take a while
> to trigger.
> 
> But v2.6.31-rc4-405-gb592972 seems to be okay, I have it running
> stable for several days now.

Comment 2 Rafael J. Wysocki 2009-08-03 16:07:10 UTC

On Monday 03 August 2009, Johannes Weiner wrote:
> On Sun, Aug 02, 2009 at 03:22:01PM -0700, Linus Torvalds wrote:
> 
> > > Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=13815
> > > Subject           : emacs -nw compilation doesn't show the error message
> > > Submitter : Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> > > Date              : 2009-07-23 06:22 (11 days old)
> > 
> > Same old pty bug, same fix: commit e043e42bdb.
> > 
> > > Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=13813
> > > Subject           : Hangups in n_tty_read()
> > > Submitter : Johannes Weiner <hannes@cmpxchg.org>
> > > Date              : 2009-07-16 18:48 (18 days old)
> > > References        :
> http://marc.info/?l=linux-kernel&m=124777019920579&w=4
> > 
> > Hmm. Worth testing that same fix, although the symptoms here are not 
> > exactly the same.
> 
> Hm, I had no debugging enabled, but I think a silent hang in
> 
>       pty_write()
>         tty_flip_buffer_push()
>           flush_to_ldisc()
> 
> can cause the receiving side
> 
>       tty_read()
>         n_tty_read()
> 
> to wait forever for updates.  I haven't looked closely.  It seems to
> be gone with your latest master in any case.