Messages in this thread Patch in this message | | | Date | Wed, 08 Oct 2014 18:54:11 -0400 | From | Jeff Mahoney <> | Subject | [PATCH] block: copy bi_vcnt in __bio_clone_fast |
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Commit 05f1dd53152173 (block: add queue flag for disabling SG merging) uses bi_vcnt to assign bio->bi_phys_segments if sg merging is disabled. When using device mapper on top of a blk-mq device (virtio_blk in my test), we'd end up overflowing the scatterlist in __blk_bios_map_sg.
__bio_clone_fast copies bi_iter and bi_io_vec but not bi_vcnt, so blk_recount_segments would report bi_phys_segments as 0. Since rq->nr_phys_segments is 0 as well, the checks to ensure that we don't exceed the queue's segment limit end up allowing more bios (and segments) to attach the a request until we finally map it. That also means we pass the BUG_ON at the beginning of virtio_queue_rq, ultimately causing memory corruption and a crash.
If we copy bi_vcnt in __bio_clone_fast, the bios and requests properly report the number of segments and everything works as expected.
Originally reported at http://bugzilla.opensuse.org/show_bug.cgi?id=888259
Reported-by: Stephen Kulow <coolo@suse.com> Signed-off-by: Jeff Mahoney <jeffm@suse.com> ---
block/bio.c | 1 + 1 file changed, 1 insertion(+)
--- a/block/bio.c +++ b/block/bio.c @@ -564,6 +564,7 @@ void __bio_clone_fast(struct bio *bio, s bio->bi_rw = bio_src->bi_rw; bio->bi_iter = bio_src->bi_iter; bio->bi_io_vec = bio_src->bi_io_vec; + bio->bi_vcnt = bio_src->bi_vcnt; } EXPORT_SYMBOL(__bio_clone_fast); -- Jeff Mahoney SUSE Labs
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