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Commit a5bfb9f8 authored by Gilad Broner's avatar Gilad Broner Committed by Matt Wagantall
Browse files

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: default avatarGilad Broner <gbroner@codeaurora.org>
parent 1f016896

block/test-iosched.c

+5 −4
Original line number Diff line number Diff line
@@ -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;