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From: Hannes Reinecke <hare@suse.de>
To: Christoph Hellwig <hch@lst.de>, axboe@fb.com
Cc: ming.lei@redhat.com, linux-block@vger.kernel.org
Subject: Re: [PATCH 1/4] block: don't decrement nr_phys_segments for physically contigous segments
Date: Thu, 16 May 2019 10:48:15 +0200
Message-ID: <ecf46792-61e5-232a-e4dc-ba7aae040002@suse.de> (raw)
In-Reply-To: <20190516084058.20678-2-hch@lst.de>

On 5/16/19 10:40 AM, Christoph Hellwig wrote:
> Currently ll_merge_requests_fn, unlike all other merge functions,
> reduces nr_phys_segments by one if the last segment of the previous,
> and the first segment of the next segement are contigous.  While this
> seems like a nice solution to avoid building smaller than possible
> requests it causes a mismatch between the segments actually present
> in the request and those iterated over by the bvec iterators, including
> __rq_for_each_bio.  This could cause overwrites of too small kmalloc
> allocations in any driver using ranged discard, or also mistrigger
> the single segment optimization in the nvme-pci driver.
> 
> We could possibly work around this by making the bvec iterators take
> the front and back segment size into account, but that would require
> moving them from the bio to the bio_iter and spreading this mess
> over all users of bvecs.  Or we could simply remove this optimization
> under the assumption that most users already build good enough bvecs,
> and that the bio merge patch never cared about this optimization
> either.  The latter is what this patch does.
> 
> Fixes: b35ba01ea697 ("nvme: support ranged discard requests")
> Fixes: 1f23816b8eb8 ("virtio_blk: add discard and write zeroes support")
> Fixes: 297910571f08 ("nvme-pci: optimize mapping single segment requests using SGLs")
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   block/blk-merge.c | 23 +----------------------
>   1 file changed, 1 insertion(+), 22 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah
HRB 21284 (AG Nürnberg)

  reply index

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-16  8:40 fix nr_phys_segments vs iterators accounting v2 Christoph Hellwig
2019-05-16  8:40 ` [PATCH 1/4] block: don't decrement nr_phys_segments for physically contigous segments Christoph Hellwig
2019-05-16  8:48   ` Hannes Reinecke [this message]
2019-05-16 13:17   ` Ming Lei
2019-05-17 23:02     ` Ming Lei
2019-05-20 11:11     ` Christoph Hellwig
2019-05-21  1:04       ` Ming Lei
2019-05-16  8:40 ` [PATCH 2/4] block: force an unlimited segment size on queues with a virt boundary Christoph Hellwig
2019-05-16  8:49   ` Hannes Reinecke
2019-05-16  8:40 ` [PATCH 3/4] block: remove the segment size check in bio_will_gap Christoph Hellwig
2019-05-16  8:49   ` Hannes Reinecke
2019-05-16  8:40 ` [PATCH 4/4] block: remove the bi_seg_{front,back}_size fields in struct bio Christoph Hellwig
2019-05-16  8:50   ` Hannes Reinecke
2019-05-20 11:17 ` fix nr_phys_segments vs iterators accounting v2 Christoph Hellwig
2019-05-21  1:09   ` Jens Axboe
2019-05-21  1:17     ` Ming Lei
2019-05-21  1:20       ` Jens Axboe
2019-05-21  1:29         ` Ming Lei
2019-05-21  5:11           ` Christoph Hellwig
2019-05-21  7:01 fix nr_phys_segments vs iterators accounting v3 Christoph Hellwig
2019-05-21  7:01 ` [PATCH 1/4] block: don't decrement nr_phys_segments for physically contigous segments Christoph Hellwig
2019-05-21  8:05   ` Ming Lei

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