linux-ext4 - Re: help about ext3 read-only issue on ext3(2.6.16.30)

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Message-ID: <20121204204508.GG7790@thunk.org>
Date:	Tue, 4 Dec 2012 15:45:08 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	qixuan wu <wuqixuan@...il.com>
Cc:	Tao Ma <tm@....ma>, Li Zefan <lizefan@...wei.com>,
	Eric Sandeen <sandeen@...hat.com>,
	Yafang Shao <laoar.shao@...il.com>,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	wuqixuan@...wei.com
Subject: Re: help about ext3 read-only issue on ext3(2.6.16.30)

On Wed, Dec 05, 2012 at 12:16:50AM +0800, qixuan wu wrote:
> 
>     Is there the possibility: one thread(A) is read_dir(directly read
> from buffer head), and another thread(B) is creating item, and fill
> this buffer header at the same time. During create item, first modify
> the last item's rec_len(let it point to next item which initially is
> zero), then fill this added new item.

This should be handled by the VFS, which uses i_mutex to protect
directories before calling the filesystem-specific lookup, rename,
readdir, etc functions.

So absent some bug where we are missing taking i_mutex (a quick check
didn't show any obvious missing paths, although I didn't do an
exhaustive code audit), we should be OK.... if we had a bug here, I
would have expected that one of the fs stress tests that we run would
have shown them up pretty quickly.

Regards,

						- Ted
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