linux-kernel - Re: [PATCH RESEND] scsi: don't use execute_in_process

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Message-ID: <20110615102022.GV8141@htj.dyndns.org>
Date:	Wed, 15 Jun 2011 12:20:22 +0200
From:	Tejun Heo <tj@...nel.org>
To:	"James E.J. Bottomley" <JBottomley@...allels.com>
Cc:	Linux SCSI List <linux-scsi@...r.kernel.org>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	lkml <linux-kernel@...r.kernel.org>,
	Steven Whitehouse <swhiteho@...hat.com>
Subject: Re: [PATCH RESEND] scsi: don't use execute_in_process_context()

On Sat, Apr 30, 2011 at 04:56:02PM +0200, Tejun Heo wrote:
> SCSI is the only subsystem which uses execute_in_process_context() and
> its use is racy against module unload.  ie. the reap work is not
> properly flushed and could still be running after the scsi module is
> unloaded.
> 
> Although execute_in_process_context() can be more efficient when the
> caller already has a context, in this case, the call paths are quite
> cold and the difference is practically meaningless.  With commit
> c8efcc25 (workqueue: allow chained queueing during destruction), the
> race condition can easily be fixed by using a dedicated workqueue and
> destroying it on module unload.
> 
> Create and use scsi_wq instead of execute_in_process_context().
> 
> * scsi_device->ew is replaced with release_work.  scsi_target->ew is
>   replaced with reap_work.
> 
> * Both works are initialized with the respective release/reap function
>   during device/target init.  scsi_target_reap_usercontext() is moved
>   upwards to avoid needing forward declaration.
> 
> * scsi_alloc_target() now explicitly flushes the reap_work of the
>   found dying target before putting it instead of depending on
>   flush_scheduled_work().
> 
> For more info on the issues, please read the following threads.
> 
>  http://thread.gmane.org/gmane.linux.scsi/62923
>  http://thread.gmane.org/gmane.linux.kernel/1124773
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Steven Whitehouse <swhiteho@...hat.com>
> --
> James, can we please get rid of execute_in_process_context()?  It
> didn't help the recent crash case which was a separate issue but
> didn't break anything either, and this is one of the last several
> users of flush_scheduled_work() that I really want to remove.

(resending due to devlivery failure on suse address)

James, ping.

-- 
tejun
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