linux-kernel - Re: [PATCH v4 1/4] [SCSI] sg: use rwsem to solve race during exclusive open

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Message-ID: <20130719211901.GA29404@logfs.org>
Date:	Fri, 19 Jul 2013 17:19:01 -0400
From:	Jörn Engel <joern@...fs.org>
To:	Vaughan Cao <vaughan.cao@...cle.com>
Cc:	dgilbert@...erlog.com, JBottomley@...allels.com,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/4] [SCSI] sg: use rwsem to solve race during
 exclusive open

On Wed, 17 July 2013 23:34:03 +0800, Vaughan Cao wrote:
> Date: Wed, 17 Jul 2013 23:34:03 +0800
> From: Vaughan Cao <vaughan.cao@...cle.com>
> To: joern@...fs.org
> Cc: dgilbert@...erlog.com, JBottomley@...allels.com,
> 	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
> 	vaughan.cao@...cle.com
> Subject: [PATCH v4 1/4] [SCSI] sg: use rwsem to solve race during
>  exclusive open
> X-Mailer: git-send-email 1.7.11.7
> 
> A race condition may happen if two threads are both trying to open the same sg
> with O_EXCL simultaneously. It's possible that they both find fsds list is
> empty and get_exclude(sdp) returns 0, then they both call set_exclude() and
> break out from wait_event_interruptible and resume open.
> 
> Now use rwsem to protect this process. Exclusive open gets write lock and
> others get read lock. The lock will be held until file descriptor is closed.
> This also leads 'exclude' only a status rather than a check mark.
> 
> Signed-off-by: Vaughan Cao <vaughan.cao@...cle.com>
Reviewed-by: Joern Engel <joern@...fs.org>

Jörn

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