On Wed, Jan 17 2018 at 10:39pm -0500, Ming Lei <[email protected]> wrote:
> On Wed, Jan 17, 2018 at 10:33:35PM -0500, Mike Snitzer wrote: > > On Wed, Jan 17 2018 at 7:54P -0500, > > Mike Snitzer <[email protected]> wrote: > > > > > But sure, I suppose there is something I missed when refactoring Ming's > > > change to get it acceptable for upstream. I went over the mechanical > > > nature of what I did many times (comparing Ming's v4 to my v5). > > > > And yes there is one subtlety that I missed. > > > > > The call to blk_mq_request_bypass_insert will only occur via > > > __blk_mq_fallback_to_insert. Which as the name implies this is not the > > > fast path. This will occur if the underlying blk-mq device cannot get > > > resources it needs in order to issue the request. Specifically: if/when > > > in __blk_mq_try_issue_directly() the hctx is stopped, or queue is > > > quiesced, or it cannot get the driver tag or dispatch_budget (in the > > > case of scsi-mq). > > > > > > The same fallback, via call to blk_mq_request_bypass_insert, occured > > > with Ming's v4 though. > > > > Turns out Ming's v4 doesn't fallback to insert for the "or it cannot get > > the driver tag or dispatch_budget" case. > > > > This patch should fix it (Laurence, please report back on if this fixes > > your list_add corruption, pretty sure it will): > > > > From: Mike Snitzer <[email protected]> > > Date: Wed, 17 Jan 2018 22:02:07 -0500 > > Subject: [PATCH] blk mq: don't blk_mq_request_bypass_insert _and_ return > > BLK_STS_RESOURCE > > > > It isn't ever valid to call blk_mq_request_bypass_insert() and return > > BLK_STS_RESOURCE. > > > > Unfortunately after commit 396eaf21ee ("blk-mq: improve DM's blk-mq IO > > merging via blk_insert_cloned_request feedback") we do just that if > > blk_mq_request_direct_issue() cannot get the resources (driver_tag or > > dispatch_budget) needed to directly issue a request. This will lead to > > "list_add corruption" because blk-mq submits the IO but then reports > > that it didn't (BLK_STS_RESOURCE in this case). > > > > Fix this by simply returning BLK_STS_RESOURCE for this case. > > > > Fixes: 396eaf21ee ("blk-mq: improve DM's blk-mq IO merging via > > blk_insert_cloned_request feedback") > > Reported-by: Laurence Oberman <[email protected]> > > Signed-off-by: Mike Snitzer <[email protected]> > > --- > > block/blk-mq.c | 12 +++++------- > > 1 file changed, 5 insertions(+), 7 deletions(-) > > > > diff --git a/block/blk-mq.c b/block/blk-mq.c > > index c418858a60ef..8bee37239255 100644 > > --- a/block/blk-mq.c > > +++ b/block/blk-mq.c > > @@ -1799,20 +1799,18 @@ static blk_status_t > > __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, > > if (q->elevator && !bypass_insert) > > goto insert; > > > > - if (!blk_mq_get_driver_tag(rq, NULL, false)) > > - goto insert; > > - > > - if (!blk_mq_get_dispatch_budget(hctx)) { > > + if (!blk_mq_get_driver_tag(rq, NULL, false) || > > + !blk_mq_get_dispatch_budget(hctx)) { > > + /* blk_mq_put_driver_tag() is idempotent */ > > blk_mq_put_driver_tag(rq); > > + if (bypass_insert) > > + return BLK_STS_RESOURCE; > > goto insert; > > } > > > > return __blk_mq_issue_directly(hctx, rq, cookie); > > insert: > > __blk_mq_fallback_to_insert(rq, run_queue, bypass_insert); > > - if (bypass_insert) > > - return BLK_STS_RESOURCE; > > - > > return BLK_STS_OK; > > } > > Hi Mike, > > I'd suggest to use the following one, which is simple and clean: > > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 4d4af8d712da..816ff5d6bc88 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -1856,15 +1856,6 @@ static blk_status_t __blk_mq_issue_directly(struct > blk_mq_hw_ctx *hctx, > return ret; > } > > -static void __blk_mq_fallback_to_insert(struct request *rq, > - bool run_queue, bool bypass_insert) > -{ > - if (!bypass_insert) > - blk_mq_sched_insert_request(rq, false, run_queue, false); > - else > - blk_mq_request_bypass_insert(rq, run_queue); > -} > - > static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, > struct request *rq, > blk_qc_t *cookie, > @@ -1892,10 +1883,10 @@ static blk_status_t > __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, > > return __blk_mq_issue_directly(hctx, rq, cookie); > insert: > - __blk_mq_fallback_to_insert(rq, run_queue, bypass_insert); > if (bypass_insert) > return BLK_STS_RESOURCE; > > + blk_mq_sched_insert_request(rq, false, run_queue, false); > return BLK_STS_OK; > } > > @@ -1911,7 +1902,7 @@ static void blk_mq_try_issue_directly(struct > blk_mq_hw_ctx *hctx, > > ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false); > if (ret == BLK_STS_RESOURCE) > - __blk_mq_fallback_to_insert(rq, true, false); > + blk_mq_sched_insert_request(rq, false, true, false); > else if (ret != BLK_STS_OK) > blk_mq_end_request(rq, ret); > That'd be another way to skin the cat.. BUT it is different than your original approach (due to the case I detailed in earlier mail). But I like the simplicity of always returning BLK_STS_RESOURCE. Reviewed-by: Mike Snitzer <[email protected]> Laurance, please test Ming's patch instead. Ming, if Laurance finds this fix works (which is should) please put a formal header on the patch and submit for Jens to pick up. Sorry about screwing this up. (feel free to re-use portions of my above patch header to help explain the problem in your header) Thanks, Mike
