block: free merged request in the caller
If we end up doing a request-to-request merge when we have completed
a bio-to-request merge, we free the request from deep down in that
path. For blk-mq-sched, the merge path has to hold the appropriate
lock, but we don't need it for freeing the request. And in fact
holding the lock is problematic, since we are now calling the
mq sched put_rq_private() hook with the lock held. Other call paths
do not hold this lock.
Fix this inconsistency by ensuring that the caller frees a merged
request. Then we can do it outside of the lock, making it both more
efficient and fixing the blk-mq-sched problem of invoking parts of
the scheduler with an unknown lock state.
Reported-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
diff --git a/block/blk-core.c b/block/blk-core.c
index 76c42f5..1d26331 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1596,7 +1596,7 @@
{
struct blk_plug *plug;
int el_ret, where = ELEVATOR_INSERT_SORT;
- struct request *req;
+ struct request *req, *free;
unsigned int request_count = 0;
unsigned int wb_acct;
@@ -1637,15 +1637,21 @@
if (el_ret == ELEVATOR_BACK_MERGE) {
if (bio_attempt_back_merge(q, req, bio)) {
elv_bio_merged(q, req, bio);
- if (!attempt_back_merge(q, req))
+ free = attempt_back_merge(q, req);
+ if (!free)
elv_merged_request(q, req, el_ret);
+ else
+ __blk_put_request(q, free);
goto out_unlock;
}
} else if (el_ret == ELEVATOR_FRONT_MERGE) {
if (bio_attempt_front_merge(q, req, bio)) {
elv_bio_merged(q, req, bio);
- if (!attempt_front_merge(q, req))
+ free = attempt_front_merge(q, req);
+ if (!free)
elv_merged_request(q, req, el_ret);
+ else
+ __blk_put_request(q, free);
goto out_unlock;
}
}
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 3826fc3..a373416 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -733,9 +733,11 @@
if (blk_rq_cpu_valid(next))
req->cpu = next->cpu;
- /* owner-ship of bio passed from next to req */
+ /*
+ * ownership of bio passed from next to req, return 'next' for
+ * the caller to free
+ */
next->bio = NULL;
- __blk_put_request(q, next);
return next;
}
@@ -763,12 +765,19 @@
struct request *next)
{
struct elevator_queue *e = q->elevator;
+ struct request *free;
if (!e->uses_mq && e->type->ops.sq.elevator_allow_rq_merge_fn)
if (!e->type->ops.sq.elevator_allow_rq_merge_fn(q, rq, next))
return 0;
- return attempt_merge(q, rq, next) != NULL;
+ free = attempt_merge(q, rq, next);
+ if (free) {
+ __blk_put_request(q, free);
+ return 1;
+ }
+
+ return 0;
}
bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 3ec52f4..ee455e7 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -234,7 +234,8 @@
}
EXPORT_SYMBOL_GPL(blk_mq_sched_move_to_dispatch);
-bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio)
+bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
+ struct request **merged_request)
{
struct request *rq;
int ret;
@@ -244,7 +245,8 @@
if (!blk_mq_sched_allow_merge(q, rq, bio))
return false;
if (bio_attempt_back_merge(q, rq, bio)) {
- if (!attempt_back_merge(q, rq))
+ *merged_request = attempt_back_merge(q, rq);
+ if (!*merged_request)
elv_merged_request(q, rq, ret);
return true;
}
@@ -252,7 +254,8 @@
if (!blk_mq_sched_allow_merge(q, rq, bio))
return false;
if (bio_attempt_front_merge(q, rq, bio)) {
- if (!attempt_front_merge(q, rq))
+ *merged_request = attempt_front_merge(q, rq);
+ if (!*merged_request)
elv_merged_request(q, rq, ret);
return true;
}
diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h
index add5f09..5954859 100644
--- a/block/blk-mq-sched.h
+++ b/block/blk-mq-sched.h
@@ -15,7 +15,8 @@
void blk_mq_sched_put_request(struct request *rq);
void blk_mq_sched_request_inserted(struct request *rq);
-bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio);
+bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
+ struct request **merged_request);
bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio);
bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq);
void blk_mq_sched_restart_queues(struct blk_mq_hw_ctx *hctx);
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index 8f91f21..d68d9c2 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -371,12 +371,16 @@
{
struct request_queue *q = hctx->queue;
struct deadline_data *dd = q->elevator->elevator_data;
- int ret;
+ struct request *free = NULL;
+ bool ret;
spin_lock(&dd->lock);
- ret = blk_mq_sched_try_merge(q, bio);
+ ret = blk_mq_sched_try_merge(q, bio, &free);
spin_unlock(&dd->lock);
+ if (free)
+ blk_mq_free_request(free);
+
return ret;
}