block: test-iosched: fix spinlock recursion

blk_run_queue() takes the queue spinlock and disabled irqs.
Consider the following callstack:

blk_run_queue
 ->__blk_run_queue
  -> scsi_request_fn
   -> blk_peek_request
    -> __elv_next_request
     -> elevator_dispatch_fn
      -> test_dispatch_requests
       -> test_dispatch_from

test_dispatch_from() will release the test-iosched spinlock
using spin_unlock_irq which will enable interrupts, however,
caller is assuming interrupts are disabled.
An interrupt can occur now and scsi soft-irq may be scheduled
with the following call stack:

scsi_softirq_done
 -> scsi_finish_command
  -> scsi_device_unbusy

scsi_device_unbusy() tries to lock the queue spinlock which was
previously locked when blk_run_queue was called, resulting in a
spinlock recursion.

Change test_dispatch_from() to use the spinlock irq save/restore variants
to prevent enabling the irq in case they were previously disabled.

Change-Id: Icaea4f9ba54771edb0302c6005047fcc5478ce8d
Signed-off-by: Gilad Broner <gbroner@codeaurora.org>

1 files changed, 5 insertions, 4 deletions

diff --git a/block/test-iosched.c b/block/test-iosched.c
index cc7d28c1ba81..9ac5d1441e0b 100644
--- a/block/test-iosched.c
+++ b/block/test-iosched.c
@@ -988,24 +988,25 @@ static int test_dispatch_from(struct request_queue *q,
 	struct test_request *test_rq;
 	struct request *rq;
 	int ret = 0;
+	unsigned long flags;
 
 	if (!ptd)
 		goto err;
 
-	spin_lock_irq(&ptd->lock);
+	spin_lock_irqsave(&ptd->lock, flags);
 	if (!list_empty(queue)) {
 		test_rq = list_entry(queue->next, struct test_request,
 				queuelist);
 		rq = test_rq->rq;
 		if (!rq) {
 			pr_err("%s: null request,return", __func__);
-			spin_unlock_irq(&ptd->lock);
+			spin_unlock_irqrestore(&ptd->lock, flags);
 			goto err;
 		}
 		list_move_tail(&test_rq->queuelist, &ptd->dispatched_queue);
 		ptd->dispatched_count++;
 		(*count)--;
-		spin_unlock_irq(&ptd->lock);
+		spin_unlock_irqrestore(&ptd->lock, flags);
 
 		print_req(rq);
 		elv_dispatch_sort(q, rq);
@@ -1013,7 +1014,7 @@ static int test_dispatch_from(struct request_queue *q,
 		ret = 1;
 		goto err;
 	}
-	spin_unlock_irq(&ptd->lock);
+	spin_unlock_irqrestore(&ptd->lock, flags);
 
 err:
 	return ret;