Call blk_mq_make_request when no ->make_request_fn is set. This is
safe now that blk_alloc_queue always sets up the pointer for make_request
based drivers. This avoids an indirect call in the blk-mq driver I/O
fast path, which is rather expensive due to spectre mitigations.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
block/blk-core.c | 26 +++++++++++++++++---------
block/blk-mq.c | 4 ++--
drivers/md/dm.c | 3 +++
include/linux/blk-mq.h | 2 ++
4 files changed, 24 insertions(+), 11 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index 311596d5dbc41..0e9e1c83e5e84 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1072,7 +1072,10 @@ blk_qc_t generic_make_request(struct bio *bio)
/* Create a fresh bio_list for all subordinate requests */
bio_list_on_stack[1] = bio_list_on_stack[0];
bio_list_init(&bio_list_on_stack[0]);
- ret = q->make_request_fn(q, bio);
+ if (q->make_request_fn)
+ ret = q->make_request_fn(q, bio);
+ else
+ ret = blk_mq_make_request(q, bio);
blk_queue_exit(q);
@@ -1112,9 +1115,7 @@ EXPORT_SYMBOL(generic_make_request);
*
* This function behaves like generic_make_request(), but does not protect
* against recursion. Must only be used if the called driver is known
- * to not call generic_make_request (or direct_make_request) again from
- * its make_request function. (Calling direct_make_request again from
- * a workqueue is perfectly fine as that doesn't recurse).
+ * to be blk-mq based.
*/
blk_qc_t direct_make_request(struct bio *bio)
{
@@ -1122,20 +1123,27 @@ blk_qc_t direct_make_request(struct bio *bio)
bool nowait = bio->bi_opf & REQ_NOWAIT;
blk_qc_t ret;
+ if (WARN_ON_ONCE(q->make_request_fn))
+ goto io_error;
if (!generic_make_request_checks(bio))
return BLK_QC_T_NONE;
if (unlikely(blk_queue_enter(q, nowait ? BLK_MQ_REQ_NOWAIT : 0))) {
if (nowait && !blk_queue_dying(q))
- bio_wouldblock_error(bio);
- else
- bio_io_error(bio);
- return BLK_QC_T_NONE;
+ goto would_block;
+ goto io_error;
}
- ret = q->make_request_fn(q, bio);
+ ret = blk_mq_make_request(q, bio);
blk_queue_exit(q);
return ret;
+
+would_block:
+ bio_wouldblock_error(bio);
+ return BLK_QC_T_NONE;
+io_error:
+ bio_io_error(bio);
+ return BLK_QC_T_NONE;
}
EXPORT_SYMBOL_GPL(direct_make_request);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 71d0894ce1c58..bcc3a2397d4ae 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1984,7 +1984,7 @@ static void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq)
*
* Returns: Request queue cookie.
*/
-static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
+blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
{
const int is_sync = op_is_sync(bio->bi_opf);
const int is_flush_fua = op_is_flush(bio->bi_opf);
@@ -2096,6 +2096,7 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
return cookie;
}
+EXPORT_SYMBOL_GPL(blk_mq_make_request); /* only for request based dm */
void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,
unsigned int hctx_idx)
@@ -2955,7 +2956,6 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
INIT_LIST_HEAD(&q->requeue_list);
spin_lock_init(&q->requeue_lock);
- q->make_request_fn = blk_mq_make_request;
q->nr_requests = set->queue_depth;
/*
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index db9e461146531..0eb93da44ea2a 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1788,6 +1788,9 @@ static blk_qc_t dm_make_request(struct request_queue *q, struct bio *bio)
int srcu_idx;
struct dm_table *map;
+ if (dm_get_md_type(md) == DM_TYPE_REQUEST_BASED)
+ return blk_mq_make_request(q, bio);
+
map = dm_get_live_table(md, &srcu_idx);
/* if we're suspended, we have to queue this io for later */
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 51fbf6f76593a..d7307795439a4 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -578,4 +578,6 @@ static inline void blk_mq_cleanup_rq(struct request *rq)
rq->q->mq_ops->cleanup_rq(rq);
}
+blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio);
+
#endif
--
2.26.1
--
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