Messages in this thread | | | Date | Mon, 27 Jul 2015 05:49:35 -0400 | Subject | Re: [PATCH v3 1/7] blk-mq: avoid access hctx->tags->cpumask before allocation | From | Ming Lei <> |
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On Tue, Jul 21, 2015 at 9:58 AM, Akinobu Mita <akinobu.mita@gmail.com> wrote: > 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?
I guess tags->cpumask need to be fixed in future, so better to just take the current patch:
[PATCH v3 1/7] blk-mq: avoid access hctx->tags->cpumask before allocation
Thanks,
> > 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. > >
-- Ming Lei
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