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From: Ming Lei <ming.lei@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org,
	Wang Shanker <shankerwangmiao@gmail.com>
Subject: Re: [PATCH 1/2] block: fix discard request merge
Date: Tue, 22 Jun 2021 15:51:38 +0800	[thread overview]
Message-ID: <YNGWioq53qoPlBMi@T590> (raw)
In-Reply-To: <20210622065309.GA29691@lst.de>

On Tue, Jun 22, 2021 at 08:53:09AM +0200, Christoph Hellwig wrote:
> On Wed, Jun 09, 2021 at 08:45:55AM +0800, Ming Lei wrote:
> > index 4d97fb6dd226..bcdff1879c34 100644
> > --- a/block/blk-merge.c
> > +++ b/block/blk-merge.c
> > @@ -559,10 +559,14 @@ static inline unsigned int blk_rq_get_max_segments(struct request *rq)
> >  static inline int ll_new_hw_segment(struct request *req, struct bio *bio,
> >  		unsigned int nr_phys_segs)
> >  {
> > -	if (req->nr_phys_segments + nr_phys_segs > blk_rq_get_max_segments(req))
> > +	if (blk_integrity_merge_bio(req->q, req, bio) == false)
> >  		goto no_merge;
> >  
> > -	if (blk_integrity_merge_bio(req->q, req, bio) == false)
> > +	/* discard request merge won't add new segment */
> > +	if (req_op(req) == REQ_OP_DISCARD)
> > +		return 1;
> > +
> > +	if (req->nr_phys_segments + nr_phys_segs > blk_rq_get_max_segments(req))
> 
> I'd rather handle this by returning UINT_MAX for discard requests from
> blk_rq_get_max_segments given that bio_attempt_discard_merge is only used
> for the !DISCARD_MERGE case anyway.

This way makes very big req->nr_phys_segments or overflows it, and may break
drivers.

At least it breaks blk_rq_nr_discard_segments(), which looks easy to fix. But we
need to audit every driver to use req->nr_phys_segments directly in case of
discard request.



Thanks,
Ming


  reply	other threads:[~2021-06-22  7:51 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-09  0:45 [PATCH 0/2] block: discard merge fix & improvement Ming Lei
2021-06-09  0:45 ` [PATCH 1/2] block: fix discard request merge Ming Lei
2021-06-22  6:53   ` Christoph Hellwig
2021-06-22  7:51     ` Ming Lei [this message]
2021-06-09  0:45 ` [PATCH 2/2] block: support bio merge for multi-range discard Ming Lei
2021-06-09  3:05   ` Wang Shanker
2021-06-09  6:12     ` Ming Lei
2021-06-09  6:57       ` Wang Shanker
2021-06-22  6:55   ` Christoph Hellwig
2021-06-22  8:35     ` Miao Wang
2021-06-14 22:00 ` [PATCH 0/2] block: discard merge fix & improvement Ming Lei
2021-06-22  3:53   ` Ming Lei

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