Messages in this thread Patch in this message | | | Subject | Re: [PATCH v3 1/7] blk-mq: avoid access hctx->tags->cpumask before allocation | From | Akinobu Mita <> | Date | Tue, 21 Jul 2015 22:58:45 +0900 |
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2015-07-19 (日) の 18:24 +0800 に Ming Lei さんは書きました: > On Sun, Jul 19, 2015 at 12:28 AM, Akinobu Mita <akinobu.mita@gmail.com> wrote: > > When unmapped hw queue is remapped after CPU topology is changed, > > hctx->tags->cpumask is set before hctx->tags is allocated in > > blk_mq_map_swqueue(). > > > > In order to fix this null pointer dereference, hctx->tags must be > > allocated before configuring hctx->tags->cpumask. > > The root cause should be that the mapping between hctx and ctx > can be changed after CPU topo is changed, then hctx->tags can > be changed too, so hctx->tags->cpumask has to be set after > hctx->tags is setup. > > > > > Fixes: f26cdc8536 ("blk-mq: Shared tag enhancements") > > I am wondering if the above commit considers CPU hotplug, and > nvme uses tag->cpumask to set irq affinity hint just during > starting queue. Looks it should be reasonalbe to > introduce one callback of mapping_changed() for handling > this kind of stuff. But this isn't related with this patch. > > > Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> > > Cc: Keith Busch <keith.busch@intel.com> > > Cc: Jens Axboe <axboe@kernel.dk> > > Cc: Ming Lei <tom.leiming@gmail.com> > > --- > > block/blk-mq.c | 9 ++++++++- > > 1 file changed, 8 insertions(+), 1 deletion(-) > > > > diff --git a/block/blk-mq.c b/block/blk-mq.c > > index 7d842db..f29f766 100644 > > --- a/block/blk-mq.c > > +++ b/block/blk-mq.c > > @@ -1821,7 +1821,6 @@ static void blk_mq_map_swqueue(struct request_queue *q) > > > > hctx = q->mq_ops->map_queue(q, i); > > cpumask_set_cpu(i, hctx->cpumask); > > - cpumask_set_cpu(i, hctx->tags->cpumask); > > ctx->index_hw = hctx->nr_ctx; > > hctx->ctxs[hctx->nr_ctx++] = ctx; > > } > > @@ -1861,6 +1860,14 @@ static void blk_mq_map_swqueue(struct request_queue *q) > > hctx->next_cpu = cpumask_first(hctx->cpumask); > > hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH; > > } > > + > > + queue_for_each_ctx(q, ctx, i) { > > + if (!cpu_online(i)) > > + continue; > > + > > + hctx = q->mq_ops->map_queue(q, i); > > + cpumask_set_cpu(i, hctx->tags->cpumask); > > If tags->cpumask is always same with hctx->cpumaks, this > CPU iterator can be avoided.
How about this patch? Or should we use cpumask_or() instead cpumask_copy?
diff --git a/block/blk-mq.c b/block/blk-mq.c index 7d842db..56f814a 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1821,7 +1821,6 @@ static void blk_mq_map_swqueue(struct request_queue *q) hctx = q->mq_ops->map_queue(q, i); cpumask_set_cpu(i, hctx->cpumask); - cpumask_set_cpu(i, hctx->tags->cpumask); ctx->index_hw = hctx->nr_ctx; hctx->ctxs[hctx->nr_ctx++] = ctx; } @@ -1846,7 +1845,10 @@ static void blk_mq_map_swqueue(struct request_queue *q) if (!set->tags[i]) set->tags[i] = blk_mq_init_rq_map(set, i); hctx->tags = set->tags[i]; - WARN_ON(!hctx->tags); + if (hctx->tags) + cpumask_copy(hctx->tags->cpumask, hctx->cpumask); + else + WARN_ON(1); /* * Set the map size to the number of mapped software queues.
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