gfs2: free disk inode which is deleted by remote node

this patch is for the same problem that Benjamin Marzinski fixes at commit b94a170e96dc416828af9d350ae2e34b70ae7347

quotation of the original problem:

---cut here---
When a file is deleted from a gfs2 filesystem on one node, a dcache entry for it may still exist on other nodes in the cluster. If this happens, gfs2 will be unable to free this file on disk. Because of this, it's possible to have a gfs2 filesystem with no files on it and no free space. With this patch, when a node receives a callback notifying it that the file is being deleted on another node, it schedules a new workqueue thread to remove the file's dcache entry.
---end cut---

after applying Benjamin's patch, I think there is still a case in which the disk inode remains even when "no space" is hit. the case is that when running d_prune_aliases() against the inode, there are one or more dentries(aliases) which have reference count number > 0. in this case the dentries won't be pruned. and even later, the reference cound becomes to 0, the dentries can still be cached in memory. unfortunately, no callback come again, things come back to the state before the callback runs. thus the on disk inode remains there until in memory inode is removed for some other reason(shrinking inode cache or unmount the gfs2 volume..).

this patch is to remove those dentries when their reference count becomes to 0 and the inode is deleted by remote node. for implementation, gfs2_dentry_delete() is added as dentry_operations.d_delete. the function returns true when the inode is deleted by remote node. in dput(), gfs2_dentry_delete() is called and since it returns true, the dentry is unhashed from dcache and then removed. when all dentries are removed, the in memory inode get removed so that the on disk inode can be freed.

Signed-off-by Wengang Wang <[email protected]>

---
 fs/gfs2/dentry.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

fs/gfs2/dentry.c +11 -0

index 022c66c..434f204 100644
@@ -107,8 +107,19 @@ static int gfs2_dhash(struct dentry *dentry, struct qstr *str)
 	return 0;
 }
 
+static int gfs2_dentry_delete(struct dentry *dentry)
+{
+	struct gfs2_inode *ginode = GFS2_I(dentry->d_inode);
+
+	if (test_bit(GLF_DEMOTE, &ginode->i_iopen_gh.gh_gl->gl_flags))
+		return 1;
+
+	return 0;
+}
+
 const struct dentry_operations gfs2_dops = {
 	.d_revalidate = gfs2_drevalidate,
 	.d_hash = gfs2_dhash,
+	.d_delete = gfs2_dentry_delete,
 };
 

Hi,

Don't worry about the wrong list, I did spot the patch anyway. I agree with the principle of what you are trying to do, but something isn't quite right. When I tried this on Friday I got a NULL pointer deref the first time I tried to touch a file on the fs.

I think it needs a bit more work, but its certainly going in the right direction,