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

[Eric Ren]

On 01/16/2017 11:13 AM, Junxiao Bi wrote:

On 01/16/2017 11:06 AM, Eric Ren wrote:

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;-)

If it is not the first one, is it another recursive locking bug? In this
case, if you don't like BUG_ON(), you can dump the call trace and print
some warning message.

Yes! I like this idea, will add it in next version, thanks!

Eric

Thanks,
Junxiao.

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;
    }