Re: [PATCH 2/2] ocfs2: fix deadlocks when taking inode lock at vfs entry points

[Eric Ren]

Hi Junxiao,

On 01/16/2017 10:46 AM, Junxiao Bi wrote:

If had_lock==true, it is a bug? I think we should BUG_ON for it, that
can help us catch bug at the first time.

Good idea! But I'm not sure if "ocfs2_setattr" is always the first one
who takes the cluster lock.
It's harder for me to name all the possible paths;-/

The BUG_ON() can help catch the path where ocfs2_setattr is not the
first one.

Yes, I understand. But, the problem is that the vfs entries calling order is 
out of our control.
I don't want to place an assertion where I'm not 100% sure it's absolutely 
right;-)

Thanks,
Eric

Thanks,
Junxiao.

+    if (had_lock)
+        arg_flags = OCFS2_META_LOCK_GETBH;
+    status = ocfs2_inode_lock_full(inode, &bh, 1, arg_flags);
       if (status < 0) {
           if (status != -ENOENT)
               mlog_errno(status);
           goto bail_unlock_rw;
       }
-    inode_locked = 1;
+    if (!had_lock) {
+        ocfs2_add_holder(lockres, &oh);
+        inode_locked = 1;
+    }
         if (size_change) {
           status = inode_newsize_ok(inode, attr->ia_size);
@@ -1260,7 +1270,8 @@ int ocfs2_setattr(struct dentry *dentry, struct
iattr *attr)
   bail_commit:
       ocfs2_commit_trans(osb, handle);
   bail_unlock:
-    if (status) {
+    if (status && inode_locked) {
+        ocfs2_remove_holder(lockres, &oh);
           ocfs2_inode_unlock(inode, 1);
           inode_locked = 0;
       }
@@ -1278,8 +1289,10 @@ int ocfs2_setattr(struct dentry *dentry,
struct iattr *attr)
           if (status < 0)
               mlog_errno(status);
       }
-    if (inode_locked)
+    if (inode_locked) {
+        ocfs2_remove_holder(lockres, &oh);
           ocfs2_inode_unlock(inode, 1);
+    }
         brelse(bh);
       return status;
@@ -1321,20 +1334,31 @@ int ocfs2_getattr(struct vfsmount *mnt,
   int ocfs2_permission(struct inode *inode, int mask)
   {
       int ret;
+    int has_locked;
+    struct ocfs2_holder oh;
+    struct ocfs2_lock_res *lockres;
         if (mask & MAY_NOT_BLOCK)
           return -ECHILD;
   -    ret = ocfs2_inode_lock(inode, NULL, 0);
-    if (ret) {
-        if (ret != -ENOENT)
-            mlog_errno(ret);
-        goto out;
+    lockres = &OCFS2_I(inode)->ip_inode_lockres;
+    has_locked = (ocfs2_is_locked_by_me(lockres) != NULL);

The same thing as ocfs2_setattr.

OK. I will think over your suggestions!

Thanks,
Eric

Thanks,
Junxiao.

+    if (!has_locked) {
+        ret = ocfs2_inode_lock(inode, NULL, 0);
+        if (ret) {
+            if (ret != -ENOENT)
+                mlog_errno(ret);
+            goto out;
+        }
+        ocfs2_add_holder(lockres, &oh);
       }
         ret = generic_permission(inode, mask);
   -    ocfs2_inode_unlock(inode, 0);
+    if (!has_locked) {
+        ocfs2_remove_holder(lockres, &oh);
+        ocfs2_inode_unlock(inode, 0);
+    }
   out:
       return ret;
   }