linux-kernel - Re: [PATCH] blk-mq: free hctx->ctxs in queue's release handler

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Date:	Thu, 4 Jun 2015 21:19:29 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Jens Axboe <axboe@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Stefan Seyfried <stefan.seyfried@...glemail.com>,
	Ming Lei <tom.leiming@...il.com>, NeilBrown <neilb@...e.de>,
	Christoph Hellwig <hch@....de>, "v4.0" <stable@...r.kernel.org>
Subject: Re: [PATCH] blk-mq: free hctx->ctxs in queue's release handler

On Thu, Jun 4, 2015 at 9:14 PM, Ming Lei <tom.leiming@...il.com> wrote:
> Now blk_cleanup_queue() can be called before calling
> del_gendisk()[1], inside which hctx->ctxs is touched
> from blk_mq_unregister_hctx(), but the variable has
> been freed by blk_cleanup_queue() at that time.
>
> So this patch moves freeing of hctx->ctxs into queue's
> release handler for fixing the oops reported by Stefan.
>
> Also ctx's kobject is embedded into each ctx pointed by
> hctx->ctxs[], which shouldn't have been released so early.

Hammm, the above line is wrong and should be removed, and
hctx->ctxs[] just stores the pointer of ctx.

Jens, if you need v1, please let me know.

>
> [1], 6cd18e711dd8075 (block: destroy bdi before blockdev is
> unregistered)
>
> Reported-by: Stefan Seyfried <stefan.seyfried@...glemail.com>
> Cc: NeilBrown <neilb@...e.de>
> Cc: Christoph Hellwig <hch@....de>
> Cc: stable@...r.kernel.org (v4.0)
> Signed-off-by: Ming Lei <tom.leiming@...il.com>
> ---
>  block/blk-mq.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index e68b71b..594eea0 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1600,6 +1600,7 @@ static int blk_mq_hctx_notify(void *data, unsigned long action,
>         return NOTIFY_OK;
>  }
>
> +/* hctx->ctxs will be freed in queue's release handler */
>  static void blk_mq_exit_hctx(struct request_queue *q,
>                 struct blk_mq_tag_set *set,
>                 struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
> @@ -1618,7 +1619,6 @@ static void blk_mq_exit_hctx(struct request_queue *q,
>
>         blk_mq_unregister_cpu_notifier(&hctx->cpu_notifier);
>         blk_free_flush_queue(hctx->fq);
> -       kfree(hctx->ctxs);
>         blk_mq_free_bitmap(&hctx->ctx_map);
>  }
>
> @@ -1891,8 +1891,12 @@ void blk_mq_release(struct request_queue *q)
>         unsigned int i;
>
>         /* hctx kobj stays in hctx */
> -       queue_for_each_hw_ctx(q, hctx, i)
> +       queue_for_each_hw_ctx(q, hctx, i) {
> +               if (!hctx)
> +                       continue;
> +               kfree(hctx->ctxs);
>                 kfree(hctx);
> +       }
>
>         kfree(q->queue_hw_ctx);
>
> --
> 1.9.1
>



-- 
Ming Lei
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