linux-kernel - Re: linux-next: Tree for Jun 26 [ vfs | block

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Date:	Wed, 26 Jun 2013 17:31:13 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>,
	Jens Axboe <axboe@...nel.dk>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	fuse-devel@...ts.sourceforge.net,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: linux-next: Tree for Jun 26 [ vfs | block | fuse (cpuidle)
 releated? ]

On Wed, Jun 26, 2013 at 5:24 PM, Thomas Petazzoni
<thomas.petazzoni@...e-electrons.com> wrote:
> Dear Sedat Dilek,
>
> On Wed, 26 Jun 2013 16:50:55 +0200, Sedat Dilek wrote:
>
>> [ TO/CC char-misc folks ]
>>
>> The CULPRIT commit [1] due to my git-bisecting is:
>>
>> commit 585d98e00ba7a5e2abe65f7a1eff631cb612289b
>> "char: misc: assign file->private_data in all cases"
>>
>> After reverting it, my system boots up fine again.
>>
>> Can someone from the char-misc folks look at that?
>
> Ok. My understanding is that the misc device registered by
> fs/fuse/dev.c:fuse_dev_init() makes the assumption that
> file->private_data == NULL when a misc device is opened. But I'm not
> sure to fully understand the code flow of the FUSE filesystem.
>
> And since it doesn't provide its own implementation of the ->open()
> operation, the misc infrastructure was leaving the file->private_data
> defined to NULL before my patch.
>
> With my patch, the file->private_data gets assigned unconditionally
> (regardless of whether the misc driver provides or does not provide a
> ->open() operation) which modifies the unwritten assumption that fuse
> was making about the initial value of file->private_data. I believe the
> assumption made by fuse over the initial value of this variable is a
> bit fragile.
>
> Maybe the FUSE code needs to be slightly adjusted to not make this
> assumption?
>

Hi Thomas,

( Fast response like a "free electron". )

That's a question for Miklos :-).

As said I have here a WUBI (fuse/loop/ext4) installation which is not
quite common, but catched some nice bugs people normally do not hit.
I can only confirm your change let's me no more boot into my system.

- Sedat -

> Best regards,
>
> Thomas
> --
> Thomas Petazzoni, Free Electrons
> Kernel, drivers, real-time and embedded Linux
> development, consulting, training and support.
> http://free-electrons.com
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