md/raid5: prefer replacing failed devices over want-replacement devices.

If a RAID5 has both a failed device and a device marked as
'WantReplacement', then we should preferentially replace the failed
device.
However the current code replaces whichever is found first.
So split into 2 loops, check fail failed/missing first, and only check
for WantReplacement if nothing is failed or missing.

Reported-by: majianpeng <majianpeng@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index d26767246d26ad1d2bb9a2da371ab1bbbdf130fc..95fcbbf3d6c9986e45f15def4620edb25652cd97 100644 (file)
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5465,10 +5465,9 @@ static int raid5_add_disk(struct mddev *mddev, struct md_rdev *rdev)
        if (rdev->saved_raid_disk >= 0 &&
            rdev->saved_raid_disk >= first &&
            conf->disks[rdev->saved_raid_disk].rdev == NULL)
-               disk = rdev->saved_raid_disk;
-       else
-               disk = first;
-       for ( ; disk <= last ; disk++) {
+               first = rdev->saved_raid_disk;
+
+       for (disk = first; disk <= last; disk++) {
                p = conf->disks + disk;
                if (p->rdev == NULL) {
                        clear_bit(In_sync, &rdev->flags);
@@ -5477,8 +5476,11 @@ static int raid5_add_disk(struct mddev *mddev, struct md_rdev *rdev)
                        if (rdev->saved_raid_disk != disk)
                                conf->fullsync = 1;
                        rcu_assign_pointer(p->rdev, rdev);
-                       break;
+                       goto out;
                }
+       }
+       for (disk = first; disk <= last; disk++) {
+               p = conf->disks + disk;
                if (test_bit(WantReplacement, &p->rdev->flags) &&
                    p->replacement == NULL) {
                        clear_bit(In_sync, &rdev->flags);
@@ -5490,6 +5492,7 @@ static int raid5_add_disk(struct mddev *mddev, struct md_rdev *rdev)
                        break;
                }
        }
+out:
        print_raid5_conf(conf);
        return err;
 }