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

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Date:	Wed, 26 Jun 2013 17:24:46 +0200
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	sedat.dilek@...il.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? ]

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?

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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