md/raid10: fix "enough" function for detecting if array is failed.

The 'enough' function is written to work with 'near' arrays only
in that is implicitly assumes that the offset from one 'group' of
devices to the next is the same as the number of copies.
In reality it is the number of 'near' copies.

So change it to make this number explicit.

This bug makes it possible to run arrays without enough drives
present, which is dangerous.
It is appropriate for an -stable kernel, but will almost certainly
need to be modified for some of them.

Cc: stable@vger.kernel.org
Reported-by: Jakub Husák <jakub@gooseman.cz>
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 1c2eb38f3c51a6dcc93148ca34b1a6a1de7aa465..0138a727c1f3c220bc91a02c9bdf720599465eb9 100644 (file)
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1512,14 +1512,16 @@ static int _enough(struct r10conf *conf, struct geom *geo, int ignore)
        do {
                int n = conf->copies;
                int cnt = 0;
+               int this = first;
                while (n--) {
-                       if (conf->mirrors[first].rdev &&
-                           first != ignore)
+                       if (conf->mirrors[this].rdev &&
+                           this != ignore)
                                cnt++;
-                       first = (first+1) % geo->raid_disks;
+                       this = (this+1) % geo->raid_disks;
                }
                if (cnt == 0)
                        return 0;
+               first = (first + geo->near_copies) % geo->raid_disks;
        } while (first != 0);
        return 1;
 }