ceph: fix geting random mds from mdsmap

For example, if we have 5 mds in the mdsmap and the states are:
m_info[5] --> [-1, 1, -1, 1, 1]

If we get a random number 1, then we should get the mds index 3 as
expected, but actually we will get index 2, which the state is -1.

The issue is that the for loop increment will advance past any "up"
MDS that was found during the while loop search.

Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

diff --git a/fs/ceph/mdsmap.c b/fs/ceph/mdsmap.c
index ce2d00d..aeec1d6 100644 (file)
--- a/fs/ceph/mdsmap.c
+++ b/fs/ceph/mdsmap.c
@@ -20,7 +20,7 @@
 int ceph_mdsmap_get_random_mds(struct ceph_mdsmap *m)
 {
        int n = 0;
-       int i;
+       int i, j;
 
        /* special case for one mds */
        if (1 == m->m_num_mds && m->m_info[0].state > 0)
@@ -35,9 +35,12 @@ int ceph_mdsmap_get_random_mds(struct ceph_mdsmap *m)
 
        /* pick */
        n = prandom_u32() % n;
-       for (i = 0; n > 0; i++, n--)
-               while (m->m_info[i].state <= 0)
-                       i++;
+       for (j = 0, i = 0; i < m->m_num_mds; i++) {
+               if (m->m_info[i].state > 0)
+                       j++;
+               if (j > n)
+                       break;
+       }
 
        return i;
 }