raid5: Set R5_Expanded on parity devices as well as data.

When reshaping a fully degraded raid5/raid6 to a larger
nubmer of devices, the new device(s) are not in-sync
and so that can make the newly grown stripe appear to be
"failed".
To avoid this, we set the R5_Expanded flag to say "Even though
this device is not fully in-sync, this block is safe so
don't treat the device as failed for this stripe".
This flag is set for data devices, not not for parity devices.

Consequently, if you have a RAID6 with two devices that are partly
recovered and a spare, and start a reshape to include the spare,
then when the reshape gets past the point where the recovery was
up to, it will think the stripes are failed and will get into
an infinite loop, failing to make progress.

So when contructing parity on an EXPAND_READY stripe,
set R5_Expanded.

Reported-by: Curt <lightspd@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 10c0d87074f0878d9ba0205f5dda9d949b92b6d6..a21dbd22a2fb85fc56c35ebfa7b0cf0e332c8341 100644 (file)
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -1818,8 +1818,11 @@ static void ops_complete_reconstruct(void *stripe_head_ref)
                struct r5dev *dev = &sh->dev[i];
 
                if (dev->written || i == pd_idx || i == qd_idx) {
-                       if (!discard && !test_bit(R5_SkipCopy, &dev->flags))
+                       if (!discard && !test_bit(R5_SkipCopy, &dev->flags)) {
                                set_bit(R5_UPTODATE, &dev->flags);
+                               if (test_bit(STRIPE_EXPAND_READY, &sh->state))
+                                       set_bit(R5_Expanded, &dev->flags);
+                       }
                        if (fua)
                                set_bit(R5_WantFUA, &dev->flags);
                        if (sync)