md/raid10: check In_sync flag in 'enough()'.

It isn't really enough to check that the rdev is present, we need to
also be sure that the device is still In_sync.

Doing this requires using rcu_dereference to access the rdev, and
holding the rcu_read_lock() to ensure the rdev doesn't disappear while
we look at it.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 11 insertions, 4 deletions

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 5169ed2a9156..aa8ba0760cac 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1633,6 +1633,7 @@ static void status(struct seq_file *seq, struct mddev *mddev)
 static int _enough(struct r10conf *conf, int previous, int ignore)
 {
         int first = 0;
+        int has_enough = 0;
         int disks, ncopies;
         if (previous) {
                 disks = conf->prev.raid_disks;
@@ -1642,21 +1643,27 @@ static int _enough(struct r10conf *conf, int previous, int ignore)
                 ncopies = conf->geo.near_copies;
         }
 
+        rcu_read_lock();
         do {
                 int n = conf->copies;
                 int cnt = 0;
                 int this = first;
                 while (n--) {
-                        if (conf->mirrors[this].rdev &&
-                            this != ignore)
+                        struct md_rdev *rdev;
+                        if (this != ignore &&
+                            (rdev = rcu_dereference(conf->mirrors[this].rdev)) &&
+                            test_bit(In_sync, &rdev->flags))
                                 cnt++;
                         this = (this+1) % disks;
                 }
                 if (cnt == 0)
-                        return 0;
+                        goto out;
                 first = (first + ncopies) % disks;
         } while (first != 0);
-        return 1;
+        has_enough = 1;
+out:
+        rcu_read_unlock();
+        return has_enough;
 }
 
 static int enough(struct r10conf *conf, int ignore)