md/raid1: Don't use next_resync to determine how far resync has progressed

next_resync is (approximately) the location for the next resync request.
However it does *not* reliably determine the earliest location
at which resync might be happening.
This is because resync requests can complete out of order, and
we only limit the number of current requests, not the distance
from the earliest pending request to the latest.

mddev->curr_resync_completed is a reliable indicator of the earliest
position at which resync could be happening.   It is updated less
frequently, but is actually reliable which is more important.

So use it to determine if a write request is before the region
being resynced and so safe from conflict.

This error can allow resync IO to interfere with normal IO which
could lead to data corruption. Hence: stable.

Fixes: 79ef3a8aa1cb1523cc231c9a90a278333c21f761
cc: stable@vger.kernel.org (v3.13+)
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 5 insertions, 7 deletions

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index b13c218997da..3b14a495c424 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -875,12 +875,10 @@ static bool need_to_wait_for_sync(struct r1conf *conf, struct bio *bio)
         if (conf->array_frozen || !bio)
                 wait = true;
         else if (conf->barrier && bio_data_dir(bio) == WRITE) {
-                if (conf->next_resync < RESYNC_WINDOW_SECTORS)
-                        wait = true;
-                else if ((conf->next_resync - RESYNC_WINDOW_SECTORS
-                                >= bio_end_sector(bio)) ||
-                         (conf->next_resync + NEXT_NORMALIO_DISTANCE
-                                <= bio->bi_iter.bi_sector))
+                if ((conf->mddev->curr_resync_completed
+                     >= bio_end_sector(bio)) ||
+                    (conf->next_resync + NEXT_NORMALIO_DISTANCE
+                     <= bio->bi_iter.bi_sector))
                         wait = false;
                 else
                         wait = true;
@@ -918,7 +916,7 @@ static sector_t wait_barrier(struct r1conf *conf, struct bio *bio)
 
         if (bio && bio_data_dir(bio) == WRITE) {
                 if (bio->bi_iter.bi_sector >=
-                    conf->next_resync) {
+                    conf->mddev->curr_resync_completed) {
                         if (conf->start_next_window == MaxSector)
                                 conf->start_next_window =
                                         conf->next_resync +