linux-kernel - Re: [PATCH] sr: Ensure disk is revalidated when media changes

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Message-ID: <BANLkTinpRJHr+293kPzS1=hCWRPamOOGfw@mail.gmail.com>
Date:	Fri, 8 Apr 2011 12:37:56 +0100
From:	Stefan Hajnoczi <stefanha@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Amit Shah <amit.shah@...hat.com>, linux-kernel@...r.kernel.org,
	Jens Axboe <axboe@...nel.dk>,
	"James E.J. Bottomley" <James.Bottomley@...e.de>,
	linux-scsi@...r.kernel.org, Markus Armbruster <armbru@...hat.com>
Subject: Re: [PATCH] sr: Ensure disk is revalidated when media changes

On Wed, Apr 6, 2011 at 11:06 AM, Tejun Heo <tj@...nel.org> wrote:
> On Tue, Apr 05, 2011 at 12:21:30PM +0530, Amit Shah wrote:
>> > But I don't think this is the correct place to do it.  The problem
>> > happens because block layer consumes the event but doesn't remember it
>> > when the time for revalidation comes.  It should be done by block
>> > layer, not sr.  Hmmm... looking at the code, the new disk event code
>> > should handle this correctly.  Was 2.6.38 showing the problem too?
>>
>> Yes, 2.6.38 shows the same problem.  I went back to ancient kernels
>> (2.6.31 on Fedora 11-alpha) which had the previous media_changed
>> infrastructure and those places too show the same behaviour (with the
>> TEST_UNIT_READY way of detecting media changes).
>
> Can you please the patch attached in the following bz and see whether
> it makes any difference?
>
>  https://bugzilla.kernel.org/show_bug.cgi?id=13029

Hi Tejun,
There is a related issue I have been discussing with Amit:
https://lkml.org/lkml/2011/3/23/156

On media change the inode size is not updated by the sr driver or the
universal cdrom driver.  A userspace process that holds a /dev/sr0
file descriptor open across media change causes all processes on the
system to see the old medium size when they do lseek(fd, 0, SEEK_END).

I think it would make sense to refresh the inode size on media change
so that even open file descriptors see the new size and a single
process cannot force a stale value for all other userspace processes
on the system.

Thoughts?

Stefan
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