linux-kernel - Re: Yet another hot unplug NULL pointer dereference (was Re: status of oops in sd_revalidate

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Message-ID: <4F6300BB.9060503@ce.jp.nec.com>
Date:	Fri, 16 Mar 2012 17:58:35 +0900
From:	"Jun'ichi Nomura" <j-nomura@...jp.nec.com>
To:	Bart Van Assche <bvanassche@....org>
CC:	Stefan Richter <stefanr@...6.in-berlin.de>,
	jbottomley@...allels.com, linux-scsi@...r.kernel.org,
	Huajun Li <huajun.li.lee@...il.com>,
	Axel Theilmann <theilmann@...-sense.de>,
	linux-kernel@...r.kernel.org
Subject: Re: Yet another hot unplug NULL pointer dereference (was Re: status
 of oops in sd_revalidate_disk?)

Hi,

On 03/14/12 03:10, Bart Van Assche wrote:
> Now that I've had some more time to think about this: has anyone
> considered to hold a reference on the SCSI host instead of the SCSI
> device as long as sd_probe_async() is active ? If sd_prep_fn() can ever
> see a NULL queuedata pointer then that means that
> scsi_host_dev_release() can get invoked while sd_prep_fn() is running.

Holding a host reference does not help, I think.
It does not stop __scsi_remove_device() setting NULL
to sdev's q->queuedata.

So, while there might be another race between sd_probe_async
and scsi_host_remove, I believe your "[PATCH] Fix device
removal NULL pointer dereference" still makes sense.

> That doesn't look correct to me.

-- 
Jun'ichi Nomura, NEC Corporation
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