md/raid1: fix counting of write targets.

There is a very small race window when writing to a
RAID1 such that if a device is marked faulty at exactly the wrong
time, the write-in-progress will not be sent to the device,
but the bitmap (if present) will be updated to say that
the write was sent.

Then if the device turned out to still be usable as was re-added
to the array, the bitmap-based-resync would skip resyncing that
block, possibly leading to corruption.  This would only be a problem
if no further writes were issued to that area of the device (i.e.
that bitmap chunk).

Suitable for any pending -stable kernel.

Cc: stable@kernel.org
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index f741f77eeb2b48aa9c51793ba778e7adb43bbcab..1ab30f64848f79023794c5170d01ef9c7d2a1a52 100644 (file)
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -911,9 +911,10 @@ static int make_request(struct request_queue *q, struct bio * bio)
                        if (test_bit(Faulty, &rdev->flags)) {
                                rdev_dec_pending(rdev, mddev);
                                r1_bio->bios[i] = NULL;
-                       } else
+                       } else {
                                r1_bio->bios[i] = bio;
-                       targets++;
+                               targets++;
+                       }
                } else
                        r1_bio->bios[i] = NULL;
        }