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authorJens Axboe <axboe@kernel.dk>2017-09-12 01:43:57 +0300
committerJens Axboe <axboe@kernel.dk>2017-09-12 01:43:57 +0300
commit157f377beb710e84bd8bc7a3c4475c0674ebebd7 (patch)
tree4ae9a47f15aab3a6c77d380bdefda5272912ded4 /block/blk-mq.h
parentbe1c704329a51cbcf019f971c5d2023c0226d9cd (diff)
downloadlinux-157f377beb710e84bd8bc7a3c4475c0674ebebd7.tar.xz
block: directly insert blk-mq request from blk_insert_cloned_request()
A NULL pointer crash was reported for the case of having the BFQ IO scheduler attached to the underlying blk-mq paths of a DM multipath device. The crash occured in blk_mq_sched_insert_request()'s call to e->type->ops.mq.insert_requests(). Paolo Valente correctly summarized why the crash occured with: "the call chain (dm_mq_queue_rq -> map_request -> setup_clone -> blk_rq_prep_clone) creates a cloned request without invoking e->type->ops.mq.prepare_request for the target elevator e. The cloned request is therefore not initialized for the scheduler, but it is however inserted into the scheduler by blk_mq_sched_insert_request." All said, a request-based DM multipath device's IO scheduler should be the only one used -- when the original requests are issued to the underlying paths as cloned requests they are inserted directly in the underlying dispatch queue(s) rather than through an additional elevator. But commit bd166ef18 ("blk-mq-sched: add framework for MQ capable IO schedulers") switched blk_insert_cloned_request() from using blk_mq_insert_request() to blk_mq_sched_insert_request(). Which incorrectly added elevator machinery into a call chain that isn't supposed to have any. To fix this introduce a blk-mq private blk_mq_request_bypass_insert() that blk_insert_cloned_request() calls to insert the request without involving any elevator that may be attached to the cloned request's request_queue. Fixes: bd166ef183c2 ("blk-mq-sched: add framework for MQ capable IO schedulers") Cc: stable@vger.kernel.org Reported-by: Bart Van Assche <Bart.VanAssche@wdc.com> Tested-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-mq.h')
-rw-r--r--block/blk-mq.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 98252b79b80b..ef15b3414da5 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -54,6 +54,7 @@ int blk_mq_alloc_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,
*/
void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
bool at_head);
+void blk_mq_request_bypass_insert(struct request *rq);
void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
struct list_head *list);