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

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Date:	Tue, 11 Jan 2011 17:23:23 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	Dave Anderson <anderson@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] /proc/kcore: fix seeking

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.

Or am I missing something?
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