[PATCH] blk-mq: don't leak preempt counter/q_usage_counter when allocating rq failed

[Ming Lei]

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

When blk_mq_get_request() failed, preempt counter isn't
released, and blk_mq_make_request() doesn't release the counter
too.

This patch fixes the issue, and makes sure that preempt counter
is only held if rq is allocated successfully. The same policy is
applied on .q_usage_counter too.

Signed-off-by: Ming Lei <min...@redhat.com>
---
 block/blk-mq.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 041f7b7fa0d6..4f2561412f13 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -301,11 +301,14 @@ static struct request *blk_mq_get_request(struct 
request_queue *q,
        struct elevator_queue *e = q->elevator;
        struct request *rq;
        unsigned int tag;
+       bool get_cpu = false;
 
        blk_queue_enter_live(q);
        data->q = q;
-       if (likely(!data->ctx))
+       if (likely(!data->ctx)) {
                data->ctx = blk_mq_get_ctx(q);
+               get_cpu = true;
+       }
        if (likely(!data->hctx))
                data->hctx = blk_mq_map_queue(q, data->ctx->cpu);
        if (op & REQ_NOWAIT)
@@ -324,6 +327,8 @@ static struct request *blk_mq_get_request(struct 
request_queue *q,
 
        tag = blk_mq_get_tag(data);
        if (tag == BLK_MQ_TAG_FAIL) {
+               if (get_cpu)
+                       blk_mq_put_ctx(data->ctx);
                blk_queue_exit(q);
                return NULL;
        }
@@ -356,12 +361,12 @@ struct request *blk_mq_alloc_request(struct request_queue 
*q, unsigned int op,
 
        rq = blk_mq_get_request(q, NULL, op, &alloc_data);
 
-       blk_mq_put_ctx(alloc_data.ctx);
-       blk_queue_exit(q);
-
        if (!rq)
                return ERR_PTR(-EWOULDBLOCK);
 
+       blk_mq_put_ctx(alloc_data.ctx);
+       blk_queue_exit(q);
+
        rq->__data_len = 0;
        rq->__sector = (sector_t) -1;
        rq->bio = rq->biotail = NULL;
@@ -407,11 +412,11 @@ struct request *blk_mq_alloc_request_hctx(struct 
request_queue *q,
 
        rq = blk_mq_get_request(q, NULL, op, &alloc_data);
 
-       blk_queue_exit(q);
-
        if (!rq)
                return ERR_PTR(-EWOULDBLOCK);
 
+       blk_queue_exit(q);
+
        return rq;
 }
 EXPORT_SYMBOL_GPL(blk_mq_alloc_request_hctx);
-- 
2.9.4