[PATCH 3/3] blk-mq: avoid access hctx->tags->cpumask before allocation

Chris J Arges chris.j.arges at canonical.com
Wed Sep 23 13:57:32 UTC 2015


Which tree did this patch come from? I don't see it in mainline.
If it isn't in mainline, it would also be good to explain if this needed
in Wily/4.2 as well.

--chris

On 09/23/2015 02:56 AM, AceLan Kao wrote:
> From: Akinobu Mita <akinobu.mita at gmail.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/1498778
> 
> 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.
> 
> Fixes: f26cdc8536 ("blk-mq: Shared tag enhancements")
> Signed-off-by: Akinobu Mita <akinobu.mita at gmail.com>
> Cc: Keith Busch <keith.busch at intel.com>
> Cc: Jens Axboe <axboe at kernel.dk>
> Cc: Ming Lei <tom.leiming at gmail.com>
> 
> Signed-off-by: AceLan Kao <acelan.kao at canonical.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 9ea3230..74f7087 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1783,7 +1783,6 @@ 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;
>  	}
> @@ -1814,6 +1813,14 @@ 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);
> +	}
>  }
>  
>  static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set)
> 




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