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authorJens Axboe <axboe@kernel.dk>2017-09-11 16:43:57 -0600
committerJens Axboe <axboe@kernel.dk>2017-09-11 16:43:57 -0600
commit157f377beb710e84bd8bc7a3c4475c0674ebebd7 (patch)
tree4ae9a47f15aab3a6c77d380bdefda5272912ded4 /block/blk-core.c
parentbe1c704329a51cbcf019f971c5d2023c0226d9cd (diff)
downloadlinux-157f377beb710e84bd8bc7a3c4475c0674ebebd7.tar.bz2
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-core.c')
-rw-r--r--block/blk-core.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/block/blk-core.c b/block/blk-core.c
index d709c0e3a2ac..aebe676225e6 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2342,7 +2342,12 @@ blk_status_t blk_insert_cloned_request(struct request_queue *q, struct request *
if (q->mq_ops) {
if (blk_queue_io_stat(q))
blk_account_io_start(rq, true);
- blk_mq_sched_insert_request(rq, false, true, false, false);
+ /*
+ * Since we have a scheduler attached on the top device,
+ * bypass a potential scheduler on the bottom device for
+ * insert.
+ */
+ blk_mq_request_bypass_insert(rq);
return BLK_STS_OK;
}