From d73f9907294c670da14baea3fb31be27879e818e Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Wed, 12 Feb 2014 16:37:30 -0500 Subject: [PATCH] dm io: fix I/O to multiple destinations Commit 003b5c5719f159f4f4bf97511c4702a0638313dd ("block: Convert drivers to immutable biovecs") broke dm-mirror due to dm-io breakage. dm-io had three possible iterators (DM_IO_PAGE_LIST, DM_IO_BVEC, DM_IO_VMA) that iterate over pages where the I/O should be performed. The switch to immutable biovecs changed the DM_IO_BVEC iterator to DM_IO_BIO. Before this change the iterator stored the pointer to a bio vector in the dpages structure. The iterator incremented the pointer in the dpages structure as it advanced over the pages. After the immutable biovecs change, the DM_IO_BIO iterator stores a pointer to the bio in the dpages structure and uses bio_advance to change the bio as it advances. The problem is that the function dispatch_io stores the content of the dpages structure into the variable old_pages and restores it before issuing I/O to each of the devices. Before the change, the statement "*dp = old_pages;" restored the iterator to its starting position. After the change, struct dpages holds a pointer to the bio, thus the statement "*dp = old_pages;" doesn't restore the iterator. Consequently, in the context of dm-mirror: only the first mirror leg is written correctly, the kernel locks up when trying to write the other mirror legs because the number of sectors to write in the where->count variable doesn't match the number of sectors returned by the iterator. This patch fixes the bug by partially reverting the original patch - it changes the code so that struct dpages holds a pointer to the bio vector, so that the statement "*dp = old_pages;" restores the iterator correctly. The field "context_u" holds the offset from the beginning of the current bio vector entry, just like the "bio->bi_iter.bi_bvec_done" field. Signed-off-by: Mikulas Patocka Signed-off-by: Mike Snitzer --- drivers/md/dm-io.c | 23 +++++++++++------------ 1 file changed, 11 insertions(+), 12 deletions(-) diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c index b2b8a10e8427..3842ac738f98 100644 --- a/drivers/md/dm-io.c +++ b/drivers/md/dm-io.c @@ -201,29 +201,28 @@ static void list_dp_init(struct dpages *dp, struct page_list *pl, unsigned offse /* * Functions for getting the pages from a bvec. */ -static void bio_get_page(struct dpages *dp, - struct page **p, unsigned long *len, unsigned *offset) +static void bio_get_page(struct dpages *dp, struct page **p, + unsigned long *len, unsigned *offset) { - struct bio *bio = dp->context_ptr; - struct bio_vec bvec = bio_iovec(bio); - *p = bvec.bv_page; - *len = bvec.bv_len; - *offset = bvec.bv_offset; + struct bio_vec *bvec = dp->context_ptr; + *p = bvec->bv_page; + *len = bvec->bv_len - dp->context_u; + *offset = bvec->bv_offset + dp->context_u; } static void bio_next_page(struct dpages *dp) { - struct bio *bio = dp->context_ptr; - struct bio_vec bvec = bio_iovec(bio); - - bio_advance(bio, bvec.bv_len); + struct bio_vec *bvec = dp->context_ptr; + dp->context_ptr = bvec + 1; + dp->context_u = 0; } static void bio_dp_init(struct dpages *dp, struct bio *bio) { dp->get_page = bio_get_page; dp->next_page = bio_next_page; - dp->context_ptr = bio; + dp->context_ptr = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter); + dp->context_u = bio->bi_iter.bi_bvec_done; } /* -- 2.20.1