linux-kernel - Re: [PATCH] drivers: mmc: reordered shutdown sequence in mmc_bld_remove

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Message-ID: <87k3lfpogy.fsf@octavius.laptop.org>
Date:	Thu, 27 Jun 2013 11:23:09 -0400
From:	Chris Ball <cjb@...top.org>
To:	Paul Taysom <taysom@...omium.org>
Cc:	Namjae Jeon <linkinjeon@...il.com>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Konstantin Dorfman <kdorfman@...eaurora.org>,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
	sonny@...omium.org, olofj@...omium.org
Subject: Re: [PATCH] drivers: mmc: reordered shutdown sequence in mmc_bld_remove_req

Hi Paul,

On Tue, Jun 04 2013, Paul Taysom wrote:
> We had a multi-partition SD-Card with two ext2 file systems. The partition
> table was getting overwritten by a race between the card removal and
> the unmount of the 2nd ext2 partition.
>
> What was observed:
> 1. Suspend/resume would call to remove the device. The clearing
>    of the device information is done asynchronously.
> 2. A request is made to unmount the file system (this is called
>    after the removal has started).
> 3. The remapping table was cleared by the asynchronous part of
>    the device removal.
> 4. A write request to the super block (block 0 of the partition)
>    was sent down and instead of being remapped to the partition
>    offset, it was remapped to block 0 of the device which is where
>    the partition table is located.
> 5. Write was queued and written resulting in the overwriting
>    of the partition table with the ext2 super block.
> 6. The mmc_queue is cleaned up.
>
> The mmc card device driver used to access SD cards, was calling del_gendisk
> before calling mmc_cleanup-queue. The comment in the mmc_blk_remove_req
> code indicated that it expected del_gendisk to block all further requests
> from being queued but it doesn't. The mmc driver uses the presences of the
> mmc_queue to determine if the request should be queued.
>
> The fix was to clean up the mmc_queue before the rest of the
> the delete partition code is called.
>
> This prevents the overwriting of the partition table.
>
> However, the umount gets an error trying to write the super block.
> The umount should be issued before the device is removed but that
> is not always possible. The umount is still needed to cleanup other
> data structures.
>
> Addresses the problem described in http://crbug.com/240815
>
> Signed-off-by: Paul Taysom <taysom@...omium.org>

Thanks, pushed to mmc-next for 3.11.

- Chris.
-- 
Chris Ball   <cjb@...top.org>   <http://printf.net/>
One Laptop Per Child
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