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block: fix deadlock between blk_mq_freeze_queue and blk_mq_dispatch_list #747

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block: fix deadlock between blk_mq_freeze_queue and blk_mq_dispatch_list #747

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10 changes: 10 additions & 0 deletions block/blk-mq.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2936,6 +2936,14 @@ static void blk_mq_dispatch_list(struct rq_list *rqs, bool from_sched)
*rqs = requeue_list;
trace_block_unplug(this_hctx->queue, depth, !from_sched);

/*
* When called from schedule(), prevent preemption and interrupts between
* ref_get and ref_put. This ensures percpu_ref_get() and percpu_ref_put()
* are atomic with respect to context switches, avoiding a deadlock with
* blk_mq_freeze_queue where a blocked task holds a percpu_ref reference.
*/
if (from_sched)
local_irq_disable();
percpu_ref_get(&this_hctx->queue->q_usage_counter);
/* passthrough requests should never be issued to the I/O scheduler */
if (is_passthrough) {
Expand All @@ -2951,6 +2959,8 @@ static void blk_mq_dispatch_list(struct rq_list *rqs, bool from_sched)
blk_mq_insert_requests(this_hctx, this_ctx, &list, from_sched);
}
percpu_ref_put(&this_hctx->queue->q_usage_counter);
if (from_sched)
local_irq_enable();
}

static void blk_mq_dispatch_multiple_queue_requests(struct rq_list *rqs)
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