[PATCH] [20/98] put stricter guards on queue dead checks

Andi Kleen
2011-07-27T00:39:32Z

From: James Bottomley <James.Bottomley@suse.de>

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>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

---
drivers/scsi/scsi_sysfs.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)

Index: linux-2.6.35.y/drivers/scsi/scsi_sysfs.c
===================================================================
--- linux-2.6.35.y.orig/drivers/scsi/scsi_sysfs.c
+++ linux-2.6.35.y/drivers/scsi/scsi_sysfs.c
@@ -319,14 +319,8 @@ static void scsi_device_dev_release_user
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));

@@ -961,6 +955,12 @@ void __scsi_remove_device(struct scsi_de
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);
}