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blk-mq: Make blk_mq_get_request() error path less confusing
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blk_mq_get_tag() can modify data->ctx. This means that in the
error path of blk_mq_get_request() data->ctx should be passed to
blk_mq_put_ctx() instead of local_ctx. Note: since blk_mq_put_ctx()
ignores its argument, this patch does not change any functionality.

References: commit 1ad43c0 ("blk-mq: don't leak preempt counter/q_usage_counter when allocating rq failed")
Reviewed-by: Ming Lei <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Johannes Thumshirn <[email protected]>
Signed-off-by: Bart Van Assche <[email protected]>
Cc: Ming Lei <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
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KAGA-KOKO authored and axboe committed Nov 3, 2017
1 parent c2e82a2 commit 21e768b
Showing 1 changed file with 7 additions and 5 deletions.
12 changes: 7 additions & 5 deletions block/blk-mq.c
Original file line number Diff line number Diff line change
Expand Up @@ -337,12 +337,14 @@ 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;
bool put_ctx_on_error = false;

blk_queue_enter_live(q);
data->q = q;
if (likely(!data->ctx))
data->ctx = local_ctx = blk_mq_get_ctx(q);
if (likely(!data->ctx)) {
data->ctx = blk_mq_get_ctx(q);
put_ctx_on_error = true;
}
if (likely(!data->hctx))
data->hctx = blk_mq_map_queue(q, data->ctx->cpu);
if (op & REQ_NOWAIT)
Expand All @@ -361,8 +363,8 @@ static struct request *blk_mq_get_request(struct request_queue *q,

tag = blk_mq_get_tag(data);
if (tag == BLK_MQ_TAG_FAIL) {
if (local_ctx) {
blk_mq_put_ctx(local_ctx);
if (put_ctx_on_error) {
blk_mq_put_ctx(data->ctx);
data->ctx = NULL;
}
blk_queue_exit(q);
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