Re: [PATCH V2] blk-mq: don't leak preempt counter/q_usage_counter when allocating rq failed

[Jens Axboe]

On 08/01/2017 06:01 PM, Ming Lei wrote:
> From: Ming Lei 
> 
> 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.

Thanks, applied for this series.

-- 
Jens Axboe

[PATCH V2] blk-mq: don't leak preempt counter/q_usage_counter when allocating rq failed

[Ming Lei]

From: Ming Lei 

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 
---
 V2: use local_ctx, and clear data->ctx if allocation fails, as
 suggested by Jens.

 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..211ef367345f 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -301,11 +301,12 @@ static struct request *blk_mq_get_request(struct 
request_queue *q,
struct elevator_queue *e = q->elevator;
struct request *rq;
unsigned int tag;
+   struct blk_mq_ctx *local_ctx = NULL;
 
blk_queue_enter_live(q);
data->q = q;
if (likely(!data->ctx))
-   data->ctx = blk_mq_get_ctx(q);
+   data->ctx = local_ctx = blk_mq_get_ctx(q);
if (likely(!data->hctx))
data->hctx = blk_mq_map_queue(q, data->ctx->cpu);
if (op & REQ_NOWAIT)
@@ -324,6 +325,10 @@ static struct request *blk_mq_get_request(struct 
request_queue *q,
 
tag = blk_mq_get_tag(data);
if (tag == BLK_MQ_TAG_FAIL) {
+   if (local_ctx) {
+   blk_mq_put_ctx(local_ctx);
+   data->ctx = NULL;
+   }
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, _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, _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