mdmon: fix, close spare activation race

The following test fails when the md_check_recovery() event triggered by
the ro->rw transition causes remove_and_add_spares() to run while mdmon
is attempting spare activation.

Result is that the kernel races to set the slot immediately after
sysfs_add_disk() writes new_dev.  mdmon thinks the spare activation
failed and declines to send the monitor a new acitve_array.  We show
degraded after the wait because the monitor cannot notify the metadata
that all disks are in_sync.

#!/bin/bash
i=0
false
while [ $? == 1 ]
do
	i=$((i+1))
	mdadm -Ss
	mdadm -CR /dev/md0 /dev/loop[0-2] -n 3 -e imsm
	mdadm -CR /dev/md1 /dev/loop[01] missing -n 3 -l 5
	mdadm --wait /dev/md1
	mdadm -E /dev/loop2 | grep -i degraded
done
echo "failed: $i"

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/managemon.c b/managemon.c
index 6662f675cc938e91a321734da3849d33d689c7c2..d020f82d35d2c630a5ac9ce38b5116c0117bf05f 100644 (file)
--- a/managemon.c
+++ b/managemon.c
@@ -498,7 +498,10 @@ static void manage_member(struct mdstat_ent *mdstat,
                newa = duplicate_aa(a);
                if (!newa)
                        goto out;
-               /* Cool, we can add a device or several. */
+               /* prevent the kernel from activating the disk(s) before we
+                * finish adding them
+                */
+               sysfs_set_str(&a->info, NULL, "sync_action", "frozen");
 
                /* Add device to array and set offset/size/slot.
                 * and open files for each newdev */