Messages in this thread Patch in this message | | | Date | Wed, 18 Jan 2012 17:31:06 +0100 | From | Jens Axboe <> | Subject | Re: Kernel crash in icq_free_icq_rcu |
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On 2012-01-18 17:24, Jens Axboe wrote: > On 2012-01-18 17:09, Tejun Heo wrote: >> On Wed, Jan 18, 2012 at 09:20:05AM -0500, Vivek Goyal wrote: >>>> Not allocating icq if request is never going to go to elevator as elevator >>>> switch was happening makes sense to me. >>>> >>>> I tried this patch. It went little further and crashed at a different >>>> place. I think this seems to be separate merging issue Tejun is trying >>>> to track down. >>> >>> Applied Tejun's debug patch to return early and not call into elevator >>> for checking whether merge is allowed or not. Things seems to be stable >>> now for me. >> >> Yeah, plug merge is calling into elevator code without any >> synchronization, so it's bound to be broken. Given plugging is >> per-task, I don't think we really need to query elevator about merging >> bio's. The request is not on elevator and plugging is part of issuing >> mechanism, not scheduling, after all. Jens, what do you think? > > Hmmm. We can bypass asking the elevator, as long as we query the > restrictions. Does the below, by itself, resolve the crash? If yes, let > me cook up a patch splitting the elv and blk rq merging logic.
Something like the below, completely untested.
But thinking about this a bit while doing it, why is the IO scheduler going away while we have plugged requests that are elvpriv?
diff --git a/block/blk-core.c b/block/blk-core.c index e6c05a9..75eba5c 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -1283,7 +1283,7 @@ static bool attempt_plug_merge(struct request_queue *q, struct bio *bio, if (rq->q != q) continue; - el_ret = elv_try_merge(rq, bio); + el_ret = blk_try_merge(rq, bio); if (el_ret == ELEVATOR_BACK_MERGE) { ret = bio_attempt_back_merge(q, rq, bio); if (ret) diff --git a/block/blk-merge.c b/block/blk-merge.c index cfcc37c..ee9ec90 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -471,3 +471,59 @@ int blk_attempt_req_merge(struct request_queue *q, struct request *rq, { return attempt_merge(q, rq, next); } + +int blk_rq_merge_ok(struct request *rq, struct bio *bio) +{ + if (!rq_mergeable(rq)) + return 0; + + /* + * Don't merge file system requests and discard requests + */ + if ((bio->bi_rw & REQ_DISCARD) != (rq->bio->bi_rw & REQ_DISCARD)) + return 0; + + /* + * Don't merge discard requests and secure discard requests + */ + if ((bio->bi_rw & REQ_SECURE) != (rq->bio->bi_rw & REQ_SECURE)) + return 0; + + /* + * different data direction or already started, don't merge + */ + if (bio_data_dir(bio) != rq_data_dir(rq)) + return 0; + + /* + * must be same device and not a special request + */ + if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special) + return 0; + + /* + * only merge integrity protected bio into ditto rq + */ + if (bio_integrity(bio) != blk_integrity_rq(rq)) + return 0; + + return 1; +} +EXPORT_SYMBOL(blk_rq_merge_ok); + +int blk_try_merge(struct request *__rq, struct bio *bio) +{ + int ret = ELEVATOR_NO_MERGE; + + /* + * we can merge and sequence is ok, check if it's possible + */ + if (blk_rq_merge_ok(__rq, bio)) { + if (blk_rq_pos(__rq) + blk_rq_sectors(__rq) == bio->bi_sector) + ret = ELEVATOR_BACK_MERGE; + else if (blk_rq_pos(__rq) - bio_sectors(bio) == bio->bi_sector) + ret = ELEVATOR_FRONT_MERGE; + } + + return ret; +} diff --git a/block/blk.h b/block/blk.h index 7efd772..a117fa9 100644 --- a/block/blk.h +++ b/block/blk.h @@ -137,6 +137,8 @@ int blk_attempt_req_merge(struct request_queue *q, struct request *rq, struct request *next); void blk_recalc_rq_segments(struct request *rq); void blk_rq_set_mixed_merge(struct request *rq); +int blk_rq_merge_ok(struct request *rq, struct bio *bio); +int blk_try_merge(struct request *rq, struct bio *bio); void blk_queue_congestion_threshold(struct request_queue *q); diff --git a/block/elevator.c b/block/elevator.c index 91e18f8..a1a75f7 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -72,39 +72,8 @@ static int elv_iosched_allow_merge(struct request *rq, struct bio *bio) */ int elv_rq_merge_ok(struct request *rq, struct bio *bio) { - if (!rq_mergeable(rq)) + if (!blk_rq_merge_ok(rq, bio)) return 0; - - /* - * Don't merge file system requests and discard requests - */ - if ((bio->bi_rw & REQ_DISCARD) != (rq->bio->bi_rw & REQ_DISCARD)) - return 0; - - /* - * Don't merge discard requests and secure discard requests - */ - if ((bio->bi_rw & REQ_SECURE) != (rq->bio->bi_rw & REQ_SECURE)) - return 0; - - /* - * different data direction or already started, don't merge - */ - if (bio_data_dir(bio) != rq_data_dir(rq)) - return 0; - - /* - * must be same device and not a special request - */ - if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special) - return 0; - - /* - * only merge integrity protected bio into ditto rq - */ - if (bio_integrity(bio) != blk_integrity_rq(rq)) - return 0; - if (!elv_iosched_allow_merge(rq, bio)) return 0; @@ -114,19 +83,13 @@ EXPORT_SYMBOL(elv_rq_merge_ok); int elv_try_merge(struct request *__rq, struct bio *bio) { - int ret = ELEVATOR_NO_MERGE; - /* * we can merge and sequence is ok, check if it's possible */ - if (elv_rq_merge_ok(__rq, bio)) { - if (blk_rq_pos(__rq) + blk_rq_sectors(__rq) == bio->bi_sector) - ret = ELEVATOR_BACK_MERGE; - else if (blk_rq_pos(__rq) - bio_sectors(bio) == bio->bi_sector) - ret = ELEVATOR_FRONT_MERGE; - } + if (elv_rq_merge_ok(__rq, bio)) + return blk_try_merge(__rq, bio); - return ret; + return ELEVATOR_NO_MERGE; } static struct elevator_type *elevator_find(const char *name) -- Jens Axboe
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