[PATCH v2 2/3] ocfs2: cluster: avoid lock order inversion in o2hb_region_pin() from drop_item

[Joseph Qi]

o2hb_heartbeat_group_drop_item() is called from configfs rmdir with the
parent directory's inode_lock held.  It calls o2hb_region_pin() ->
o2nm_depend_item() -> configfs_depend_item(), which acquires the configfs
root inode_lock.  This creates a parent -> root inode_lock nesting that
could deadlock against paths taking root -> parent (e.g. subsystem
unregistration).

Fix this by using configfs_depend_item_unlocked() when o2hb_region_pin()
is called from a configfs callback context.  This variant skips the root
inode_lock when caller and target are in the same subsystem, which is
safe because VFS already holds a lock preventing unregistration.

Add o2nm_depend_item_unlocked() wrapper and a from_callback parameter to
o2hb_region_pin() to select the appropriate variant.

Fixes: 58a3158a5d17 ("ocfs2/cluster: Pin/unpin o2hb regions")
Signed-off-by: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>
---
 fs/ocfs2/cluster/heartbeat.c   | 17 ++++++++++-------
 fs/ocfs2/cluster/nodemanager.c |  6 ++++++
 fs/ocfs2/cluster/nodemanager.h |  1 +
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/fs/ocfs2/cluster/heartbeat.c b/fs/ocfs2/cluster/heartbeat.c
index 5ca1d9c0c6575..b9395835523e2 100644
--- a/fs/ocfs2/cluster/heartbeat.c
+++ b/fs/ocfs2/cluster/heartbeat.c
@@ -146,7 +146,7 @@ static unsigned int o2hb_dependent_users;
  * In global heartbeat mode, we pin/unpin all o2hb regions. This solution
  * works for both file system and userdlm domains.
  */
-static int o2hb_region_pin(const char *region_uuid);
+static int o2hb_region_pin(const char *region_uuid, bool from_callback);
 static void o2hb_region_unpin(const char *region_uuid);
 
 /* Only sets a new threshold if there are no active regions.
@@ -2188,7 +2188,7 @@ static void o2hb_heartbeat_group_drop_item(struct config_group *group,
 
 	if (bitmap_weight(o2hb_quorum_region_bitmap,
 			   O2NM_MAX_REGIONS) <= O2HB_PIN_CUT_OFF)
-		o2hb_region_pin(NULL);
+		o2hb_region_pin(NULL, true);
 
 unlock:
 	spin_unlock(&o2hb_live_lock);
@@ -2330,7 +2330,7 @@ EXPORT_SYMBOL_GPL(o2hb_setup_callback);
  * In local, we only pin the matching region. In global we pin all the active
  * regions.
  */
-static int o2hb_region_pin(const char *region_uuid)
+static int o2hb_region_pin(const char *region_uuid, bool from_callback)
 {
 	int ret = 0, found;
 	struct o2hb_region *reg, *pinned;
@@ -2385,7 +2385,10 @@ static int o2hb_region_pin(const char *region_uuid)
 		spin_unlock(&o2hb_live_lock);
 
 		/* Ignore ENOENT only for local hb (userdlm domain) */
-		ret = o2nm_depend_item(&pinned->hr_item);
+		if (from_callback)
+			ret = o2nm_depend_item_unlocked(&pinned->hr_item);
+		else
+			ret = o2nm_depend_item(&pinned->hr_item);
 
 		spin_lock(&o2hb_live_lock);
 		if (!ret) {
@@ -2483,8 +2486,8 @@ static int o2hb_region_inc_user(const char *region_uuid)
 
 	/* local heartbeat */
 	if (!o2hb_global_heartbeat_active()) {
-	    ret = o2hb_region_pin(region_uuid);
-	    goto unlock;
+		ret = o2hb_region_pin(region_uuid, false);
+		goto unlock;
 	}
 
 	/*
@@ -2497,7 +2500,7 @@ static int o2hb_region_inc_user(const char *region_uuid)
 
 	if (bitmap_weight(o2hb_quorum_region_bitmap,
 			   O2NM_MAX_REGIONS) <= O2HB_PIN_CUT_OFF)
-		ret = o2hb_region_pin(NULL);
+		ret = o2hb_region_pin(NULL, false);
 
 unlock:
 	spin_unlock(&o2hb_live_lock);
diff --git a/fs/ocfs2/cluster/nodemanager.c b/fs/ocfs2/cluster/nodemanager.c
index e1f8f577ce5d6..ebdf0bdbb8c69 100644
--- a/fs/ocfs2/cluster/nodemanager.c
+++ b/fs/ocfs2/cluster/nodemanager.c
@@ -778,6 +778,12 @@ int o2nm_depend_item(struct config_item *item)
 	return configfs_depend_item(&o2nm_cluster_group.cs_subsys, item);
 }
 
+int o2nm_depend_item_unlocked(struct config_item *item)
+{
+	return configfs_depend_item_unlocked(&o2nm_cluster_group.cs_subsys,
+					     item);
+}
+
 void o2nm_undepend_item(struct config_item *item)
 {
 	configfs_undepend_item(item);
diff --git a/fs/ocfs2/cluster/nodemanager.h b/fs/ocfs2/cluster/nodemanager.h
index 39006005427b6..ca3483fb54504 100644
--- a/fs/ocfs2/cluster/nodemanager.h
+++ b/fs/ocfs2/cluster/nodemanager.h
@@ -64,6 +64,7 @@ void o2nm_node_get(struct o2nm_node *node);
 void o2nm_node_put(struct o2nm_node *node);
 
 int o2nm_depend_item(struct config_item *item);
+int o2nm_depend_item_unlocked(struct config_item *item);
 void o2nm_undepend_item(struct config_item *item);
 int o2nm_depend_node(u8 node_num);
 void o2nm_undepend_node(u8 node_num);
-- 
2.39.3