[SCSI] Stop accepting SCSI requests before removing a device

Avoid that the code for requeueing SCSI requests triggers a
crash by making sure that that code isn't scheduled anymore
after a device has been removed.

Also, source code inspection of __scsi_remove_device() revealed
a race condition in this function: no new SCSI requests must be
accepted for a SCSI device after device removal started.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

2 files changed, 13 insertions, 5 deletions

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 8af6a6497c4f..b58327758c58 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -155,13 +155,14 @@ static void __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, int unbusy)
 
         /*
          * Requeue this command.  It will go before all other commands
-         * that are already in the queue.
+         * that are already in the queue. Schedule requeue work under
+         * lock such that the kblockd_schedule_work() call happens
+         * before blk_cleanup_queue() finishes.
          */
         spin_lock_irqsave(q->queue_lock, flags);
         blk_requeue_request(q, cmd->request);
-        spin_unlock_irqrestore(q->queue_lock, flags);
-
         kblockd_schedule_work(q, &device->requeue_work);
+        spin_unlock_irqrestore(q->queue_lock, flags);
 }
 
 /*
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 9aa578a5da11..d19d7e99626d 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -967,13 +967,20 @@ void __scsi_remove_device(struct scsi_device *sdev)
                 device_del(dev);
         } else
                 put_device(&sdev->sdev_dev);
+
+        /*
+         * Stop accepting new requests and wait until all queuecommand() and
+         * scsi_run_queue() invocations have finished before tearing down the
+         * device.
+         */
         scsi_device_set_state(sdev, SDEV_DEL);
+        blk_cleanup_queue(sdev->request_queue);
+        cancel_work_sync(&sdev->requeue_work);
+
         if (sdev->host->hostt->slave_destroy)
                 sdev->host->hostt->slave_destroy(sdev);
         transport_destroy_device(dev);
 
-        /* Freeing the queue signals to block that we're done */
-        blk_cleanup_queue(sdev->request_queue);
         put_device(dev);
 }