Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753205AbbGSKYT (ORCPT ); Sun, 19 Jul 2015 06:24:19 -0400 Received: from mail-ig0-f173.google.com ([209.85.213.173]:37647 "EHLO mail-ig0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752098AbbGSKYR (ORCPT ); Sun, 19 Jul 2015 06:24:17 -0400 MIME-Version: 1.0 In-Reply-To: <1437236903-31617-2-git-send-email-akinobu.mita@gmail.com> References: <1437236903-31617-1-git-send-email-akinobu.mita@gmail.com> <1437236903-31617-2-git-send-email-akinobu.mita@gmail.com> Date: Sun, 19 Jul 2015 18:24:16 +0800 Message-ID: Subject: Re: [PATCH v3 1/7] blk-mq: avoid access hctx->tags->cpumask before allocation From: Ming Lei To: Akinobu Mita Cc: Linux Kernel Mailing List , Keith Busch , Jens Axboe Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2568 Lines: 74 On Sun, Jul 19, 2015 at 12:28 AM, Akinobu Mita 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 > Cc: Keith Busch > Cc: Jens Axboe > Cc: Ming Lei > --- > 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. > + } > } > > static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set) > -- > 1.9.1 > -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/