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 <[email protected]> --- block/blk-merge.c | 23 +---------------------- 1 file changed, 1 insertion(+), 22 deletions(-)
Reviewed-by: Hannes Reinecke <[email protected]> Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking [email protected] +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: Felix Imendörffer, Mary Higgins, Sri Rasiah HRB 21284 (AG Nürnberg)
