Re: hangs on boot in 9984d7394618df9

From: Stephen Warren <swarren@wwwdotorg.org>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Doug Anderson <dianders@chromium.org>,
	Nathan Zimmer <nzimmer@sgi.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	linux-fsdevel@vger.kernel.org,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	David Woodhouse <dwmw2@infradead.org>,
	stable@vger.kernel.org,
	"linux-next@vger.kernel.org" <linux-next@vger.kernel.org>
Subject: Re: hangs on boot in 9984d7394618df9
Date: Mon, 08 Apr 2013 17:20:30 -0600	[thread overview]
Message-ID: <516350BE.2000106@wwwdotorg.org> (raw)
In-Reply-To: <20130408230658.GY4068@ZenIV.linux.org.uk>

On 04/08/2013 05:06 PM, Al Viro wrote:
> On Mon, Apr 08, 2013 at 03:45:31PM -0700, Doug Anderson wrote:
>> Hi,
>>
>> On Mon, Apr 8, 2013 at 3:17 PM, Stephen Warren <swarren@wwwdotorg.org> wrote:
>>>> Anyway, I've just pushed a splitup of that commit (carved in 3 pieces)
>>>> into vfs.git#pipe-splitup; could you check which part triggers that
>>>> hang?  Should propagate in a few...
>>>
>>> It looks like "pipe: unify ->release() and ->open()" introduces the
>>> problem. Note that I had to add a prototype for fifo_open() before the
>>> structs that reference it for that commit to compile.
>>
>> It sounds like Stephen has provided you the info you needed so not
>> doing any extra testing now, but I figured I'd chime in that I hit
>> problems this morning with linux-next and it appears to be the same
>> thing.  I did a revert of 9984d7394618df9 and (plus a revert of a
>> handful of patches to the same file) and problems are resolved.  The
>> failure case is really weird in that everything works well booting to
>> a simple /bin/bash but fails when you do more complex tasks.
>>
>> Anyway: If you need some extra testing feel free to CC me.
> 
> Folks, see if vfs.git#experimental works for you; the PITA had apparently
> been caused by change of open() semantics for /proc/<pid>/fd/<some_pipe> -
> it started to behave like a FIFO, i.e. wait for peer to show up.  Normally
> that's not a problem, but if you have closed e.g. the write end of a pipe
> and try to open /proc/<pid>/fd/<read_end_of_pipe>, you'll get open() waiting
> for writers to appear.  Which isn't what we used to do here (open succeeded
> immediately) and apparently that was enough to trip drakut.
> 
> Branch head should be at 574179469f7370aadb9cbac1ceca7c3723c17bee.

That branch works.

Thanks!