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| author | Mikulas Patocka <mpatocka@redhat.com> | 2014-02-12 16:37:30 -0500 |
|---|---|---|
| committer | Mike Snitzer <snitzer@redhat.com> | 2014-02-17 11:00:05 -0500 |
| commit | d73f9907294c670da14baea3fb31be27879e818e (patch) | |
| tree | aebcc204b06a8c68b003adb66623281a7fc00840 /drivers/md/dm-io.c | |
| parent | 4d1662a30dde6e545086fe0e8fd7e474c4e0b639 (diff) | |
| download | linux-d73f9907294c670da14baea3fb31be27879e818e.tar.bz2 | |
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/dm-io.c')
| -rw-r--r-- | drivers/md/dm-io.c | 23 |
1 files 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; } /* |