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    SubjectRe: [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@oracle.com>
    > To: joern@logfs.org
    > Cc: dgilbert@interlog.com, JBottomley@parallels.com,
    > linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
    > vaughan.cao@oracle.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@oracle.com>
    Reviewed-by: Joern Engel <joern@logfs.org>

    Jörn

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