Re: [PATCH] blk-mq: fix use-after-free in blk_mq_exit_sched

[John Garry <john.garry@xxxxxxxxxx>]

> > Reported-by:syzbot+77ba3d171a25c56756ea@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Fixes: d97e594c5166 ("blk-mq: Use request queue-wide tags for tagset-wide sbitmap")
> > Cc: John Garry<john.garry@xxxxxxxxxx>
> > Signed-off-by: Ming Lei<ming.lei@xxxxxxxxxx>
Tested-by: John Garry <john.garry@xxxxxxxxxx>
Reviewed-by: John Garry <john.garry@xxxxxxxxxx>

>> ---
> >   block/blk-mq-sched.c | 4 +++-
> >   1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
> > index a9182d2f8ad3..80273245d11a 100644
> > --- a/block/blk-mq-sched.c
> > +++ b/block/blk-mq-sched.c
> > @@ -680,6 +680,7 @@ void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
> >   {
> >   	struct blk_mq_hw_ctx *hctx;
> >   	unsigned int i;
> > +	unsigned int flags = 0;
> >   
> >   	queue_for_each_hw_ctx(q, hctx, i) {
> >   		blk_mq_debugfs_unregister_sched_hctx(hctx);
> > @@ -687,12 +688,13 @@ void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
> >   			e->type->ops.exit_hctx(hctx, i);
> >   			hctx->sched_data = NULL;
> >   		}
> > +		flags = hctx->flags;
> >   	}
> >   	blk_mq_debugfs_unregister_sched(q);
> >   	if (e->type->ops.exit_sched)
> >   		e->type->ops.exit_sched(e);
> >   	blk_mq_sched_tags_teardown(q);
> > -	if (blk_mq_is_sbitmap_shared(q->tag_set->flags))
> > +	if (blk_mq_is_sbitmap_shared(flags))

I suppose we could also have this also, but not nice to snoop around 
sbitmap internals:
	if (q->sched_bitmap_tags.sb.map)
		blk_mq_exit_sched_shared_sbitmap(q);

> >   		blk_mq_exit_sched_shared_sbitmap(q);
> >   	q->elevator = NULL;
> >   }


Thanks,
John