Commit 74d6f030 authored Nov 11, 2019 by Xiubo Li Committed by Ilya Dryomov Nov 25, 2019

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>

parent 6b0a8774

fs/ceph/mdsmap.c

+7 −4

Original line number	Diff line number	Diff line
		@@ -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;
		}

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