ocfs2/cluster: unlock the o2hb_live_lock before the o2nm_depend_item()

In the following situation, the down_write() will be called under the spin_lock(), which may lead a soft lockup:
o2hb_region_inc_user
spin_lock(&o2hb_live_lock)
o2hb_region_pin
o2nm_depend_item

    configfs_depend_item
     inode_lock
      down_write
      -->here may sleep and reschedule

So we should unlock the o2hb_live_lock before the o2nm_depend_item(), and get item reference in advance to prevent the region to be released.

Signed-off-by Alex Chen <[email protected]>

Reviewed-by Yiwen Jiang <[email protected]>

Reviewed-by Jun Piao <[email protected]>

---
 fs/ocfs2/cluster/heartbeat.c | 7 +++++++
 1 file changed, 7 insertions(+)

fs/ocfs2/cluster/heartbeat.c +7 -0

index d020604..07b2fdc 100644
@@ -2399,8 +2399,15 @@ static int o2hb_region_pin(const char *region_uuid)
 		if (reg->hr_item_pinned || reg->hr_item_dropped)
 			goto skip_pin;
 
+		config_item_get(&reg->hr_item);
+		spin_unlock(&o2hb_live_lock);
+
 		/* Ignore ENOENT only for local hb (userdlm domain) */
 		ret = o2nm_depend_item(&reg->hr_item);
+
+		config_item_put(&reg->hr_item);
+		spin_lock(&o2hb_live_lock);
+
 		if (!ret) {
 			mlog(ML_CLUSTER, "Pin region %s\n", uuid);
 			reg->hr_item_pinned = 1;

Hi Alex,

For local heartbeat mode, I understand that if the region is not found, o2hb_live_lock won't be released. And if the region is found, it doesn't have to iterate the next region. So I agree with your fix in this case.

But I still don't get how to make sure the safe iteration in case of global heartbeat mode.

Thanks,
Joseph

Quoted 42 lines · alex chen

In the following situation, the down_write() will be called under the spin_lock(), which may lead a soft lockup:
o2hb_region_inc_user
spin_lock(&o2hb_live_lock)
o2hb_region_pin
o2nm_depend_item

    configfs_depend_item
     inode_lock
      down_write
      -->here may sleep and reschedule

So we should unlock the o2hb_live_lock before the o2nm_depend_item(), and get item reference in advance to prevent the region to be released.

Signed-off-by Alex Chen <[email protected]>

Reviewed-by Yiwen Jiang <[email protected]>

Reviewed-by Jun Piao <[email protected]>

---
 fs/ocfs2/cluster/heartbeat.c | 7 +++++++
 1 file changed, 7 insertions(+)

fs/ocfs2/cluster/heartbeat.c +7 -0

index d020604..07b2fdc 100644
@@ -2399,8 +2399,15 @@ static int o2hb_region_pin(const char *region_uuid)
 		if (reg->hr_item_pinned || reg->hr_item_dropped)
 			goto skip_pin;
 
+		config_item_get(&reg->hr_item);
+		spin_unlock(&o2hb_live_lock);
+
 		/* Ignore ENOENT only for local hb (userdlm domain) */
 		ret = o2nm_depend_item(&reg->hr_item);
+
+		config_item_put(&reg->hr_item);
+		spin_lock(&o2hb_live_lock);
+
 		if (!ret) {
 			mlog(ML_CLUSTER, "Pin region %s\n", uuid);
 			reg->hr_item_pinned = 1;