linux-kernel - Re: Kernel crashing on eject SD card

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Message-ID: <20120214162858.GM12117@google.com>
Date:	Tue, 14 Feb 2012 08:28:58 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Jun'ichi Nomura <j-nomura@...jp.nec.com>
Cc:	Naveen Goswamy <naveen.goswamy@...ymtl.ca>,
	Jens Axboe <axboe@...nel.dk>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	Dave Jones <davej@...hat.com>, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org
Subject: Re: Kernel crashing on eject SD card

Hello,

On Tue, Feb 14, 2012 at 08:14:40PM +0900, Jun'ichi Nomura wrote:
> The following commit has changed __blkdev_get() to end up calling
> sd_revalidate_disk() without getting a refcount of scsi_device:
> 
>   commit 1196f8b814f32cd04df334abf47648c2a9fd8324
>   Author: Tejun Heo <tj@...nel.org>
>   Date:   Thu Apr 21 20:54:45 2011 +0200
> 
>     block: rescan partitions on invalidated devices on -ENOMEDIA too
> 
> that could lead to oops like this:
> 
>   process A                  process B
>   ----------------------------------------------
>   sys_open
>     __blkdev_get
>       sd_open
>         returns -ENOMEDIUM
>                              scsi_remove_device
>                                <scsi_device torn down>
>       rescan_partitions
>         sd_revalidate_disk
>           <oops>
> 
> Should "revalidate_disk" of block_device_operations work
> without successful open()?
> 
> If so, sd_revalidate_disk() (and possibly other drivers) needs to be
> fixed. (e.g. use scsi_disk_get/put by itself)
> 
> If not, __blkdev_get() or rescan_partision() should avoid calling
> "revalidate_disk" for -ENOMEDIUM case.

Hmmm... right, that's a problem.  Missed rescan_partitions() calling
into driver.  What we should probably do is separating out
invalidation & partition shoot down into a separate function, say
trucate_disk(), and call that on -ENOMEDIUM instead of
rescan_partitions().  All that's necessary is killing the partition
devices (and maybe zapping device size to zero).  Any one interested
in trying it?

Thanks.

-- 
tejun
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