@@ -430,6 +430,11 @@ int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
if (success)
return 0;
+ if (flags & BLK_MQ_REQ_FORCE) {
+ percpu_ref_get(&q->q_usage_counter);
+ return 0;
+ }
+
if (flags & BLK_MQ_REQ_NOWAIT)
return -EBUSY;
@@ -448,6 +448,13 @@ enum {
BLK_MQ_REQ_INTERNAL = (__force blk_mq_req_flags_t)(1 << 2),
/* set RQF_PREEMPT */
BLK_MQ_REQ_PREEMPT = (__force blk_mq_req_flags_t)(1 << 3),
+
+ /*
+ * force to allocate request and caller has to make sure queue
+ * won't be frozen completely during allocation, and this flag
+ * is only applied after queue freeze is started
+ */
+ BLK_MQ_REQ_FORCE = (__force blk_mq_req_flags_t)(1 << 4),
};
struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
When one hctx becomes inactive, there may be requests allocated from this hctx, we can't queue them to the inactive hctx, one approach is to re-submit them via one active hctx. However, the request queue may have been started to freeze, and allocating request becomes not possible. Add flag of BLK_MQ_REQ_FORCE to allow block layer to allocate request in this case becasue the queue won't be frozen completely before all requests allocated from inactive hctx are completed. The similar approach has been applied in commit 8dc765d438f1 ("SCSI: fix queue cleanup race before queue initialization is done"). This way can help on other request dependency case too, such as, storage device side has some problem, and IO request can't be queued to device successfully, and passthrough request is required to fix the device problem. If queue freeze just comes before allocating passthrough request, hang will be triggered in queue freeze process, IO process and context for allocating passthrough request forever. See commit 01e99aeca397 ("blk-mq: insert passthrough request into hctx->dispatch directly") for background of this kind of issue. Cc: John Garry <john.garry@huawei.com> Cc: Bart Van Assche <bvanassche@acm.org> Cc: Hannes Reinecke <hare@suse.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ming Lei <ming.lei@redhat.com> --- block/blk-core.c | 5 +++++ include/linux/blk-mq.h | 7 +++++++ 2 files changed, 12 insertions(+)