ocfs2/dlm: Migrate lockres with no locks if it has a reference

o2dlm was not migrating resources with zero locks because it assumed that that
resource would get purged by dlm_thread. However, some usage patterns involve
creating and dropping locks at a high rate leading to the migrate thread seeing
zero locks but the purge thread seeing an active reference. When this happens,
the dlm_thread cannot purge the resource and the migrate thread sees no reason
to migrate that resource. The spell is broken when the migrate thread catches
the resource with a lock.

The fix is to make the migrate thread also consider the reference map.

This usage pattern can be triggered by userspace on userdlm locks and flocks.

Signed-off-by: Sunil Mushran <sunil.mushran@oracle.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>

diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c
index f564b0e5f80d8c89e08eeba4a5e133b24cb67373..59f0f6bdfc62110141ca7ad413dc51abadd4b3c8 100644 (file)
--- a/fs/ocfs2/dlm/dlmmaster.c
+++ b/fs/ocfs2/dlm/dlmmaster.c
@@ -2346,7 +2346,8 @@ static void dlm_deref_lockres_worker(struct dlm_work_item *item, void *data)
  */
 static int dlm_is_lockres_migrateable(struct dlm_ctxt *dlm,
                                      struct dlm_lock_resource *res,
-                                     int *numlocks)
+                                     int *numlocks,
+                                     int *hasrefs)
 {
        int ret;
        int i;
@@ -2356,6 +2357,9 @@ static int dlm_is_lockres_migrateable(struct dlm_ctxt *dlm,
 
        assert_spin_locked(&res->spinlock);
 
+       *numlocks = 0;
+       *hasrefs = 0;
+
        ret = -EINVAL;
        if (res->owner == DLM_LOCK_RES_OWNER_UNKNOWN) {
                mlog(0, "cannot migrate lockres with unknown owner!\n");
@@ -2386,7 +2390,13 @@ static int dlm_is_lockres_migrateable(struct dlm_ctxt *dlm,
        }
 
        *numlocks = count;
-       mlog(0, "migrateable lockres having %d locks\n", *numlocks);
+
+       count = find_next_bit(res->refmap, O2NM_MAX_NODES, 0);
+       if (count < O2NM_MAX_NODES)
+               *hasrefs = 1;
+
+       mlog(0, "%s: res %.*s, Migrateable, locks %d, refs %d\n", dlm->name,
+            res->lockname.len, res->lockname.name, *numlocks, *hasrefs);
 
 leave:
        return ret;
@@ -2408,7 +2418,7 @@ static int dlm_migrate_lockres(struct dlm_ctxt *dlm,
        const char *name;
        unsigned int namelen;
        int mle_added = 0;
-       int numlocks;
+       int numlocks, hasrefs;
        int wake = 0;
 
        if (!dlm_grab(dlm))
@@ -2417,13 +2427,13 @@ static int dlm_migrate_lockres(struct dlm_ctxt *dlm,
        name = res->lockname.name;
        namelen = res->lockname.len;
 
-       mlog(0, "migrating %.*s to %u\n", namelen, name, target);
+       mlog(0, "%s: Migrating %.*s to %u\n", dlm->name, namelen, name, target);
 
        /*
         * ensure this lockres is a proper candidate for migration
         */
        spin_lock(&res->spinlock);
-       ret = dlm_is_lockres_migrateable(dlm, res, &numlocks);
+       ret = dlm_is_lockres_migrateable(dlm, res, &numlocks, &hasrefs);
        if (ret < 0) {
                spin_unlock(&res->spinlock);
                goto leave;
@@ -2431,10 +2441,8 @@ static int dlm_migrate_lockres(struct dlm_ctxt *dlm,
        spin_unlock(&res->spinlock);
 
        /* no work to do */
-       if (numlocks == 0) {
-               mlog(0, "no locks were found on this lockres! done!\n");
+       if (numlocks == 0 && !hasrefs)
                goto leave;
-       }
 
        /*
         * preallocate up front
@@ -2459,14 +2467,14 @@ static int dlm_migrate_lockres(struct dlm_ctxt *dlm,
         * find a node to migrate the lockres to
         */
 
-       mlog(0, "picking a migration node\n");
        spin_lock(&dlm->spinlock);
        /* pick a new node */
        if (!test_bit(target, dlm->domain_map) ||
            target >= O2NM_MAX_NODES) {
                target = dlm_pick_migration_target(dlm, res);
        }
-       mlog(0, "node %u chosen for migration\n", target);
+       mlog(0, "%s: res %.*s, Node %u chosen for migration\n", dlm->name,
+            namelen, name, target);
 
        if (target >= O2NM_MAX_NODES ||
            !test_bit(target, dlm->domain_map)) {
@@ -2667,7 +2675,7 @@ int dlm_empty_lockres(struct dlm_ctxt *dlm, struct dlm_lock_resource *res)
 {
        int ret;
        int lock_dropped = 0;
-       int numlocks;
+       int numlocks, hasrefs;
 
        spin_lock(&res->spinlock);
        if (res->owner != dlm->node_num) {
@@ -2681,8 +2689,8 @@ int dlm_empty_lockres(struct dlm_ctxt *dlm, struct dlm_lock_resource *res)
        }
 
        /* No need to migrate a lockres having no locks */
-       ret = dlm_is_lockres_migrateable(dlm, res, &numlocks);
-       if (ret >= 0 && numlocks == 0) {
+       ret = dlm_is_lockres_migrateable(dlm, res, &numlocks, &hasrefs);
+       if (ret >= 0 && numlocks == 0 && !hasrefs) {
                spin_unlock(&res->spinlock);
                goto leave;
        }
@@ -2915,6 +2923,12 @@ static u8 dlm_pick_migration_target(struct dlm_ctxt *dlm,
                }
                queue++;
        }
+
+       nodenum = find_next_bit(res->refmap, O2NM_MAX_NODES, 0);
+       if (nodenum < O2NM_MAX_NODES) {
+               spin_unlock(&res->spinlock);
+               return nodenum;
+       }
        spin_unlock(&res->spinlock);
        mlog(0, "have not found a suitable target yet! checking domain map\n");