From: Ming Lei <ming....@redhat.com>

This patch makes it possible to pause request allocation for
the legacy block layer by calling blk_mq_freeze_queue() and
blk_mq_unfreeze_queue().

Signed-off-by: Ming Lei <ming....@redhat.com>
[ bvanassche: Combined two patches into one, edited a comment and made sure
  REQ_NOWAIT is handled properly in blk_old_get_request() ]
Signed-off-by: Bart Van Assche <bart.vanass...@wdc.com>
Reviewed-by: Christoph Hellwig <h...@lst.de>
Reviewed-by: Johannes Thumshirn <jthumsh...@suse.de>
Cc: Ming Lei <ming....@redhat.com>
Cc: Hannes Reinecke <h...@suse.com>
---
 block/blk-core.c | 12 ++++++++++++
 block/blk-mq.c   | 10 ++--------
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 14f7674fa0b1..265a69511c47 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -610,6 +610,9 @@ void blk_set_queue_dying(struct request_queue *q)
                }
                spin_unlock_irq(q->queue_lock);
        }
+
+       /* Make blk_queue_enter() reexamine the DYING flag. */
+       wake_up_all(&q->mq_freeze_wq);
 }
 EXPORT_SYMBOL_GPL(blk_set_queue_dying);
 
@@ -1395,16 +1398,22 @@ static struct request *blk_old_get_request(struct 
request_queue *q,
                                           unsigned int op, gfp_t gfp_mask)
 {
        struct request *rq;
+       int ret = 0;
 
        WARN_ON_ONCE(q->mq_ops);
 
        /* create ioc upfront */
        create_io_context(gfp_mask, q->node);
 
+       ret = blk_queue_enter(q, !(gfp_mask & __GFP_DIRECT_RECLAIM) ||
+                             (op & REQ_NOWAIT));
+       if (ret)
+               return ERR_PTR(ret);
        spin_lock_irq(q->queue_lock);
        rq = get_request(q, op, NULL, gfp_mask);
        if (IS_ERR(rq)) {
                spin_unlock_irq(q->queue_lock);
+               blk_queue_exit(q);
                return rq;
        }
 
@@ -1576,6 +1585,7 @@ void __blk_put_request(struct request_queue *q, struct 
request *req)
                blk_free_request(rl, req);
                freed_request(rl, sync, rq_flags);
                blk_put_rl(rl);
+               blk_queue_exit(q);
        }
 }
 EXPORT_SYMBOL_GPL(__blk_put_request);
@@ -1857,8 +1867,10 @@ static blk_qc_t blk_queue_bio(struct request_queue *q, 
struct bio *bio)
         * Grab a free request. This is might sleep but can not fail.
         * Returns with the queue unlocked.
         */
+       blk_queue_enter_live(q);
        req = get_request(q, bio->bi_opf, bio, GFP_NOIO);
        if (IS_ERR(req)) {
+               blk_queue_exit(q);
                __wbt_done(q->rq_wb, wb_acct);
                if (PTR_ERR(req) == -ENOMEM)
                        bio->bi_status = BLK_STS_RESOURCE;
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 076cbab9c3e0..8766587ae8b8 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -125,7 +125,8 @@ void blk_freeze_queue_start(struct request_queue *q)
        freeze_depth = atomic_inc_return(&q->mq_freeze_depth);
        if (freeze_depth == 1) {
                percpu_ref_kill(&q->q_usage_counter);
-               blk_mq_run_hw_queues(q, false);
+               if (q->mq_ops)
+                       blk_mq_run_hw_queues(q, false);
        }
 }
 EXPORT_SYMBOL_GPL(blk_freeze_queue_start);
@@ -255,13 +256,6 @@ void blk_mq_wake_waiters(struct request_queue *q)
        queue_for_each_hw_ctx(q, hctx, i)
                if (blk_mq_hw_queue_mapped(hctx))
                        blk_mq_tag_wakeup_all(hctx->tags, true);
-
-       /*
-        * If we are called because the queue has now been marked as
-        * dying, we need to ensure that processes currently waiting on
-        * the queue are notified as well.
-        */
-       wake_up_all(&q->mq_freeze_wq);
 }
 
 bool blk_mq_can_queue(struct blk_mq_hw_ctx *hctx)
-- 
2.14.2

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