Before bio is submitted, it is safe to borrow .bi_error. This
patch uses .bi_error as index of pre-allocated page in bio, so
that we can avoid to mess .bi_vcnt. Especially the old way
will not work any more when multipage bvec is introduced.

Signed-off-by: Ming Lei <tom.leim...@gmail.com>
---
 drivers/md/raid1.c  | 12 ++++++++++--
 drivers/md/raid10.c | 14 ++++++++++----
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index c4791fbd69ac..8904a9149671 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -2811,13 +2811,14 @@ static sector_t raid1_sync_request(struct mddev *mddev, 
sector_t sector_nr,
                                len = sync_blocks<<9;
                }
 
+               /* borrow .bi_error as pre-allocated page index */
                for (i = 0 ; i < conf->raid_disks * 2; i++) {
                        bio = r1_bio->bios[i];
                        if (bio->bi_end_io) {
-                               page = mdev_get_page_from_bio(bio, 
bio->bi_vcnt);
+                               page = mdev_get_page_from_bio(bio, 
bio->bi_error++);
                                if (bio_add_page(bio, page, len, 0) == 0) {
                                        /* stop here */
-                                       mdev_put_page_to_bio(bio, bio->bi_vcnt, 
page);
+                                       mdev_put_page_to_bio(bio, 
--bio->bi_error, page);
                                        while (i > 0) {
                                                i--;
                                                bio = r1_bio->bios[i];
@@ -2836,6 +2837,13 @@ static sector_t raid1_sync_request(struct mddev *mddev, 
sector_t sector_nr,
                sync_blocks -= (len>>9);
        } while (r1_bio->bios[disk]->bi_vcnt < RESYNC_PAGES);
  bio_full:
+       /* return .bi_error back to bio */
+       for (i = 0 ; i < conf->raid_disks * 2; i++) {
+               bio = r1_bio->bios[i];
+               if (bio->bi_end_io)
+                       bio->bi_error = 0;
+       }
+
        r1_bio->sectors = nr_sectors;
 
        if (mddev_is_clustered(mddev) &&
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index b7dfbca869a3..9cfc22cd1330 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -3348,7 +3348,6 @@ static sector_t raid10_sync_request(struct mddev *mddev, 
sector_t sector_nr,
 
                        bio = r10_bio->devs[i].bio;
                        bio_reset(bio);
-                       bio->bi_error = -EIO;
                        rcu_read_lock();
                        rdev = rcu_dereference(conf->mirrors[d].rdev);
                        if (rdev == NULL || test_bit(Faulty, &rdev->flags)) {
@@ -3392,7 +3391,6 @@ static sector_t raid10_sync_request(struct mddev *mddev, 
sector_t sector_nr,
                        /* Need to set up for writing to the replacement */
                        bio = r10_bio->devs[i].repl_bio;
                        bio_reset(bio);
-                       bio->bi_error = -EIO;
 
                        sector = r10_bio->devs[i].addr;
                        bio->bi_next = biolist;
@@ -3435,14 +3433,15 @@ static sector_t raid10_sync_request(struct mddev 
*mddev, sector_t sector_nr,
                        len = (max_sector - sector_nr) << 9;
                if (len == 0)
                        break;
+               /* borrow .bi_error as pre-allocated page index */
                for (bio= biolist ; bio ; bio=bio->bi_next) {
                        struct bio *bio2;
-                       page = mdev_get_page_from_bio(bio, bio->bi_vcnt);
+                       page = mdev_get_page_from_bio(bio, bio->bi_error++);
                        if (bio_add_page(bio, page, len, 0))
                                continue;
 
                        /* stop here */
-                       mdev_put_page_to_bio(bio, bio->bi_vcnt, page);
+                       mdev_put_page_to_bio(bio, --bio->bi_error, page);
                        for (bio2 = biolist;
                             bio2 && bio2 != bio;
                             bio2 = bio2->bi_next) {
@@ -3456,6 +3455,13 @@ static sector_t raid10_sync_request(struct mddev *mddev, 
sector_t sector_nr,
                sector_nr += len>>9;
        } while (biolist->bi_vcnt < RESYNC_PAGES);
  bio_full:
+       /* return .bi_error back to bio, and set resync's as -EIO */
+       for (bio= biolist ; bio ; bio=bio->bi_next)
+               if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery))
+                       bio->bi_error = -EIO;
+               else
+                       bio->bi_error = 0;
+
        r10_bio->sectors = nr_sectors;
 
        while (biolist) {
-- 
2.7.4

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