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authorMikulas Patocka <mpatocka@redhat.com>2014-02-12 16:37:30 -0500
committerMike Snitzer <snitzer@redhat.com>2014-02-17 11:00:05 -0500
commitd73f9907294c670da14baea3fb31be27879e818e (patch)
treeaebcc204b06a8c68b003adb66623281a7fc00840 /drivers/md
parent4d1662a30dde6e545086fe0e8fd7e474c4e0b639 (diff)
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 <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'drivers/md')
-rw-r--r--drivers/md/dm-io.c23
1 files changed, 11 insertions, 12 deletions
diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index b2b8a10e842..3842ac738f9 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;
}
/*