blk-mq: add warning to __blk_mq_run_hw_queue() for ints disabled

We recently had a bug in the IPR SCSI driver, where it would end up
making the SCSI mid layer run the mq hardware queue with interrupts
disabled. This isn't legal, since the software queue locking relies
on never being grabbed from interrupt context. Additionally, drivers
that set BLK_MQ_F_BLOCKING may schedule from this context.

Add a WARN_ON_ONCE() to catch bad users up front.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index b70a4ad78b635798d0bfa2e25a7a755827079ac9..a5d369dc762202822fc8b9ce9845370c9e3096fc 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1097,9 +1097,19 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
 {
        int srcu_idx;
 
+       /*
+        * We should be running this queue from one of the CPUs that
+        * are mapped to it.
+        */
        WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask) &&
                cpu_online(hctx->next_cpu));
 
+       /*
+        * We can't run the queue inline with ints disabled. Ensure that
+        * we catch bad users of this early.
+        */
+       WARN_ON_ONCE(in_interrupt());
+
        if (!(hctx->flags & BLK_MQ_F_BLOCKING)) {
                rcu_read_lock();
                blk_mq_sched_dispatch_requests(hctx);