linux-kernel - Re: [PATCH 5/5] fat: add mutex lock to fat_build

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Message-ID: <87390va2o6.fsf@devron.myhome.or.jp>
Date:	Wed, 31 Oct 2012 09:46:49 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Namjae Jeon <linkinjeon@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Namjae Jeon <namjae.jeon@...sung.com>,
	Ravishankar N <ravi.n1@...sung.com>,
	Amit Sahrawat <a.sahrawat@...sung.com>
Subject: Re: [PATCH 5/5] fat: add mutex lock to fat_build_inode

Namjae Jeon <linkinjeon@...il.com> writes:

> 2012/10/30, Andrew Morton <akpm@...ux-foundation.org>:
>> On Sun, 28 Oct 2012 10:53:43 +0900
>> Namjae Jeon <linkinjeon@...il.com> wrote:
>>
>>> From: Namjae Jeon <namjae.jeon@...sung.com>
>>>
>>> fat_nfs_get_inode does not hold i_mutex of parent directory.So add
>>> lock to fat_build_inode.
>>
> Hi. Andrew.
>> Well..  why?  Presumably this patch fixes some race.  A good
>> description of that race would be useful - partly because others may
>> then be able to suggest alternative ways of fixing that bug.
> We are making use of fat_build_inode to build the inode using 'i_pos'.
> Since, this function is local to FAT and when mounted over NFS. We can
> make use of FAT parallely from local NFS Server and mounted from NFS
> client. So, in order to avoid race to multiple regeneration for the
> same 'i_pos' - we have introduced this locking.

This lock fixes the NFS patches. FAT inode is embedded into
directory. So usual local ->lookup path is exclusive by
inode->i_mutex. But NFS patches (current -mm, IIRC) introduce the new
path for FH => inode lookup.

So, this lock is introduced.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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