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

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Message-ID: <CA+icZUXijuvgQGGqvpPUzrzgC0n4ipo3eFf9vnFa+4jHoTDgDw@mail.gmail.com>
Date:	Wed, 26 Jun 2013 17:36:03 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	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>
Subject: Re: linux-next: Tree for Jun 26 [ vfs | block | fuse (cpuidle)
 releated? ]

On Wed, Jun 26, 2013 at 5:32 PM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Wed, Jun 26, 2013 at 05:24:46PM +0200, Thomas Petazzoni 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?
>
> As the FUSE code was working properly before this change, I think this
> misc core change needs to be reverted, so I'll go do that in a bit.
>

Good, sound reasonable.

I was not aware that char-misc and fuse code is so interwoven (hope
this is the right word).

- Sedat -

> thanks,
>
> greg k-h
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