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    Subject[PATCH 06/91] put stricter guards on queue dead checks
    2.6.27-longterm review patch.  If anyone has any objections, please let us know.

    ------------------

    commit 86cbfb5607d4b81b1a993ff689bbd2addd5d3a9b upstream.

    SCSI uses request_queue->queuedata == NULL as a signal that the queue
    is dying. We set this state in the sdev release function. However,
    this allows a small window where we release the last reference but
    haven't quite got to this stage yet and so something will try to take
    a reference in scsi_request_fn and oops. It's very rare, but we had a
    report here, so we're pushing this as a bug fix

    The actual fix is to set request_queue->queuedata to NULL in
    scsi_remove_device() before we drop the reference. This causes
    correct automatic rejects from scsi_request_fn as people who hold
    additional references try to submit work and prevents anything from
    getting a new reference to the sdev that way.

    Signed-off-by: James Bottomley <James.Bottomley@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
    ---
    drivers/scsi/scsi_sysfs.c | 16 ++++++++--------
    1 files changed, 8 insertions(+), 8 deletions(-)

    Index: longterm-2.6.27/drivers/scsi/scsi_sysfs.c
    ===================================================================
    --- longterm-2.6.27.orig/drivers/scsi/scsi_sysfs.c 2012-02-05 22:34:34.876915660 +0100
    +++ longterm-2.6.27/drivers/scsi/scsi_sysfs.c 2012-02-05 22:34:35.776914691 +0100
    @@ -317,14 +317,8 @@
    kfree(evt);
    }

    - if (sdev->request_queue) {
    - sdev->request_queue->queuedata = NULL;
    - /* user context needed to free queue */
    - scsi_free_queue(sdev->request_queue);
    - /* temporary expedient, try to catch use of queue lock
    - * after free of sdev */
    - sdev->request_queue = NULL;
    - }
    + /* NULL queue means the device can't be used */
    + sdev->request_queue = NULL;

    scsi_target_reap(scsi_target(sdev));

    @@ -950,6 +944,12 @@
    if (sdev->host->hostt->slave_destroy)
    sdev->host->hostt->slave_destroy(sdev);
    transport_destroy_device(dev);
    +
    + /* cause the request function to reject all I/O requests */
    + sdev->request_queue->queuedata = NULL;
    +
    + /* Freeing the queue signals to block that we're done */
    + scsi_free_queue(sdev->request_queue);
    put_device(dev);
    }




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