[PATCH] dm: bio split bvec fix

The code that handles bios that span table target boundaries by breaking
them up into smaller bios will not split an individual struct bio_vec into
more than two pieces.  Sometimes more than that are required.

This patch adds a loop to break the second piece up into as many pieces as
are necessary.

Cc: "Abhishek Gupta" <abhishekgupt@gmail.com>
Cc: Dan Smith <danms@us.ibm.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 24 insertions, 19 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 88d60202b9db..26b08ee425c7 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -533,30 +533,35 @@ static void __clone_and_map(struct clone_info *ci)
 
         } else {
                 /*
-                 * Create two copy bios to deal with io that has
-                 * been split across a target.
+                 * Handle a bvec that must be split between two or more targets.
                  */
                 struct bio_vec *bv = bio->bi_io_vec + ci->idx;
+                sector_t remaining = to_sector(bv->bv_len);
+                unsigned int offset = 0;
 
-                clone = split_bvec(bio, ci->sector, ci->idx,
-                                   bv->bv_offset, max);
-                __map_bio(ti, clone, tio);
+                do {
+                        if (offset) {
+                                ti = dm_table_find_target(ci->map, ci->sector);
+                                max = max_io_len(ci->md, ci->sector, ti);
 
-                ci->sector += max;
-                ci->sector_count -= max;
-                ti = dm_table_find_target(ci->map, ci->sector);
-
-                len = to_sector(bv->bv_len) - max;
-                clone = split_bvec(bio, ci->sector, ci->idx,
-                                   bv->bv_offset + to_bytes(max), len);
-                tio = alloc_tio(ci->md);
-                tio->io = ci->io;
-                tio->ti = ti;
-                memset(&tio->info, 0, sizeof(tio->info));
-                __map_bio(ti, clone, tio);
+                                tio = alloc_tio(ci->md);
+                                tio->io = ci->io;
+                                tio->ti = ti;
+                                memset(&tio->info, 0, sizeof(tio->info));
+                        }
+
+                        len = min(remaining, max);
+
+                        clone = split_bvec(bio, ci->sector, ci->idx,
+                                           bv->bv_offset + offset, len);
+
+                        __map_bio(ti, clone, tio);
+
+                        ci->sector += len;
+                        ci->sector_count -= len;
+                        offset += to_bytes(len);
+                } while (remaining -= len);
 
-                ci->sector += len;
-                ci->sector_count -= len;
                 ci->idx++;
         }
 }