On Tue, Nov 17, 2020 at 02:07:01PM +0000, Satya Tangirala wrote:
> @@ -275,11 +331,24 @@ static struct bio *blk_bio_segment_split(struct 
> request_queue *q,
>               bvprvp = &bvprv;
>       }
>  
> +     /*
> +      * The input bio's number of sectors is assumed to be aligned to
> +      * bio_sectors_alignment. If that's the case, then this function should
> +      * ensure that aligned_segs == nsegs and aligned_sectors == sectors if
> +      * the bio is not going to be split.
> +      */
> +     WARN_ON(aligned_segs != nsegs || aligned_sectors != sectors);
>       *segs = nsegs;
>       return NULL;
>  split:
> -     *segs = nsegs;
> -     return bio_split(bio, sectors, GFP_NOIO, bs);
> +     *segs = aligned_segs;
> +     if (WARN_ON(aligned_sectors == 0))
> +             goto err;
> +     return bio_split(bio, aligned_sectors, GFP_NOIO, bs);
> +err:
> +     bio->bi_status = BLK_STS_IOERR;
> +     bio_endio(bio);
> +     return bio;
>  }
[...]
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 55bcee5dc032..de5c97ab8e5a 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2161,6 +2161,9 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio)
>       blk_queue_bounce(q, &bio);
>       __blk_queue_split(&bio, &nr_segs);
>  
> +     if (bio->bi_status != BLK_STS_OK)
> +             goto queue_exit;
> +

Note that as soon as bio_endio() is called, the bio may be freed.

So accessing the bio after that is not correct.

- Eric


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