Re: [PATCH] block: don't call rq_qos_ops->done_bio if the bio isn't tracked

[Christoph Hellwig <hch@infradead.org>]

On Fri, Sep 24, 2021 at 07:07:04PM +0800, Ming Lei wrote:
> rq_qos framework is only applied on request based driver, so:
> 
> 1) rq_qos_done_bio() needn't to be called for bio based driver
> 
> 2) rq_qos_done_bio() needn't to be called for bio which isn't tracked,
> such as bios ended from error handling code.
> 
> Especially in bio_endio():
> 
> 1) request queue is referred via bio->bi_bdev->bd_disk->queue, which
> may be gone since request queue refcount may not be held in above two
> cases
> 
> 2) q->rq_qos may be freed in blk_cleanup_queue() when calling into
> __rq_qos_done_bio()
> 
> Fix the potential kernel panic by not calling rq_qos_ops->done_bio if
> the bio isn't tracked. This way is safe because both ioc_rqos_done_bio()
> and blkcg_iolatency_done_bio() are nop if the bio isn't tracked.

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

> @@ -1466,7 +1466,7 @@ void bio_endio(struct bio *bio)
>  	if (!bio_integrity_endio(bio))
>  		return;
>  
> -	if (bio->bi_bdev)
> +	if (bio->bi_bdev && bio_flagged(bio, BIO_TRACKED))
>  		rq_qos_done_bio(bio->bi_bdev->bd_disk->queue, bio);

We should probbly also drop the request_queue argument to
rq_qos_done_bio in a separate cleanup.