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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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