linux-kernel - Re: [PATCH] fuse: hold i_mutex in fuse_file_fallocate()

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Date:	Tue, 18 Jun 2013 01:49:27 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Brian Foster <bfoster@...hat.com>
Cc:	Maxim Patlasov <MPatlasov@...allels.com>,
	fuse-devel <fuse-devel@...ts.sourceforge.net>,
	Anand Avati <avati@...hat.com>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	devel@...nvz.org
Subject: Re: [PATCH] fuse: hold i_mutex in fuse_file_fallocate() - v2

On Thu, Jun 13, 2013 at 1:46 PM, Brian Foster <bfoster@...hat.com> wrote:
> On 06/13/2013 04:16 AM, Maxim Patlasov wrote:
>> Changing size of a file on server and local update (fuse_write_update_size)
>> should be always protected by inode->i_mutex. Otherwise a race like this is
>> possible:
>>
>> 1. Process 'A' calls fallocate(2) to extend file (~FALLOC_FL_KEEP_SIZE).
>> fuse_file_fallocate() sends FUSE_FALLOCATE request to the server.
>> 2. Process 'B' calls ftruncate(2) shrinking the file. fuse_do_setattr()
>> sends shrinking FUSE_SETATTR request to the server and updates local i_size
>> by i_size_write(inode, outarg.attr.size).
>> 3. Process 'A' resumes execution of fuse_file_fallocate() and calls
>> fuse_write_update_size(inode, offset + length). But 'offset + length' was
>> obsoleted by ftruncate from previous step.
>>
>> Changed in v2 (thanks Brian and Anand for suggestions):
>>  - made relation between mutex_lock() and fuse_set_nowrite(inode) more
>>    explicit and clear.
>>  - updated patch description to use ftruncate(2) in example
>>
>> Signed-off-by: Maxim V. Patlasov <MPatlasov@...allels.com>

Thanks, applied.

Miklos
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