On Wed, Jun 05, 2019 at 03:10:51PM +0100, John Garry wrote:
> On 31/05/2019 03:27, Ming Lei wrote:
> > index 32b8ad3d341b..49d73d979cb3 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -2433,6 +2433,11 @@ static bool __blk_mq_alloc_rq_map(struct blk_mq_tag_set *set, int hctx_idx)
> > {
> > int ret = 0;
> >
>
> Hi Ming,
>
> > + if ((set->flags & BLK_MQ_F_HOST_TAGS) && hctx_idx) {
> > + set->tags[hctx_idx] = set->tags[0];
>
> Here we set all tags same as that of hctx index 0.
>
> > + return true;
>
>
> As such, I think that the error handling in __blk_mq_alloc_rq_maps() is made
> a little fragile:
>
> __blk_mq_alloc_rq_maps(struct blk_mq_tag_set *set)
> {
> int i;
>
> for (i = 0; i < set->nr_hw_queues; i++)
> if (!__blk_mq_alloc_rq_map(set, i))
> goto out_unwind;
>
> return 0;
>
> out_unwind:
> while (--i >= 0)
> blk_mq_free_rq_map(set->tags[i]);
>
> return -ENOMEM;
> }
>
> If __blk_mq_alloc_rq_map(, i > 1) fails for when BLK_MQ_F_HOST_TAGS FLAG is
> set (even though today it can't), then we would try to free set->tags[0]
> multiple times.
Good catch, and the issue can be addressed easily by setting set->hctx[i] as
NULL, then check 'tags' in blk_mq_free_rq_map().
Thanks,
Ming
