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Commit 388c4bcb authored by Sunil Mushran's avatar Sunil Mushran Committed by Joel Becker
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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: default avatarSunil Mushran <sunil.mushran@oracle.com>
Signed-off-by: default avatarJoel Becker <joel.becker@oracle.com>
parent 771f8bc7

fs/ocfs2/dlm/dlmmaster.c

+27 −13
Original line number Diff line number Diff line
@@ -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");