linux-kernel - Re: [PATCH] /proc/kcore: fix seeking

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Message-ID: <20110114094442.GB10219@cr0.nay.redhat.com>
Date:	Fri, 14 Jan 2011 17:44:42 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Américo Wang <xiyou.wangcong@...il.com>,
	Dave Anderson <anderson@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] /proc/kcore: fix seeking

On Tue, Jan 11, 2011 at 05:23:23PM +0100, Frederic Weisbecker wrote:
>On Wed, Jan 12, 2011 at 12:04:37AM +0800, Américo Wang wrote:
>> On Mon, Jan 10, 2011 at 09:42:29AM -0500, Dave Anderson wrote:
>> >From: Dave Anderson <anderson@...hat.com>
>> >
>> >Commit 34aacb2920667d405a8df15968b7f71ba46c8f18
>> >("procfs: Use generic_file_llseek in /proc/kcore")
>> >broke seeking on /proc/kcore.  This changes it back
>> >to use default_llseek in order to restore the original
>> >behavior.
>> >
>> >The problem with generic_file_llseek is that it only
>> >allows seeks up to inode->i_sb->s_maxbytes, which is
>> >2GB-1 on procfs, where the memory file offset values in
>> >the /proc/kcore PT_LOAD segments may exceed or start
>> >beyond that offset value.
>> >
>> 
>> Is the race solved? Using default_llseek() still races
>> with read_kcore() on fpos, AFAIK.
>
>Hmm, how does it race there?
>
>read_kcore() manipulates fpos, which can't be changed behind
>us inside the read callback as it's a snapshot. Also read_kcore()
>can change the value of fpos, which is writed back to file->fpos
>from sys_read().
>
>So the last resulting race here the natural one between
>seeking and reading, which is up to the user to take care
>of.

Hmm, I just read the changelog of commit
34aacb2920667d405a8df15968b7f71ba46c8f18, which claims to fix
the race. So anything changed in vfs layer after that?

Thanks.


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