linux-ext4 - Re: BUG? a suspected race bug at ext3_xattr_block

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Message-ID: <20091210154202.GB26516@atrey.karlin.mff.cuni.cz>
Date:	Thu, 10 Dec 2009 16:42:03 +0100
From:	Jan Kara <jack@...e.cz>
To:	홍신 shin hong <hongshin@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: BUG? a suspected race bug at ext3_xattr_block_set()

  Hi,

> I am reporting a suspected data race bug from ext3/xattr.c in Linux 2.6.31.
  Thank you for your report.

> In ext3_xattr_block_set(), it accesses bs->bh->b_data
> while it does not hold lock_buffer(bs->bh).
> 
> However, there is no lock_buffer(bs->bh) and unlock_buffer(bs->bh)
> for guarding the access (at line 794).
  Yes, but we don't really look at the content of bs->bh->b_data. We
just compare the pointers and for that we definitely don't need the
lock. So I don't see problem. If you still do, please tell me more
details (like a sample of code executions of two threads which race).
Thanks.

								Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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