Patch "make nfs_atomic_open() call d_drop() on all ->open_context() errors." has been added to the 4.6-stable tree

This is a note to let you know that I've just added the patch titled

    make nfs_atomic_open() call d_drop() on all ->open_context() errors.

to the 4.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
make-nfs_atomic_open-call-d_drop-on-all-open_context-errors.patch
and it can be found in the queue-4.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Al Viro <[email protected]>
Date: Mon, 20 Jun 2016 13:14:36 -0400
Subject: make nfs_atomic_open() call d_drop() on all ->open_context() errors.

From: Al Viro <[email protected]>

commit d20cb71dbf3487f24549ede1a8e2d67579b4632e upstream.

In "NFSv4: Move dentry instantiation into the NFSv4-specific atomic open code" unconditional d_drop() after the ->open_context() had been removed. It had been correct for success cases (there ->open_context() itself had been doing dcache manipulations), but not for error ones. Only one of those (ENOENT) got a compensatory d_drop() added in that commit, but in fact it should've been done for all errors. As it is, the case of O_CREAT non-exclusive open on a hashed negative dentry racing with e.g. symlink creation from another client ended up with ->open_context() getting an error and proceeding to call nfs_lookup(). On a hashed dentry, which would've instantly triggered BUG_ON() in d_materialise_unique() (or, these days, its equivalent in d_splice_alias()).

---
 fs/nfs/dir.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -1527,9 +1527,9 @@ int nfs_atomic_open(struct inode *dir, s
 		err = PTR_ERR(inode);
 		trace_nfs_atomic_open_exit(dir, ctx, open_flags, err);
 		put_nfs_open_context(ctx);
+		d_drop(dentry);
 		switch (err) {
 		case -ENOENT:
-			d_drop(dentry);
 			d_add(dentry, NULL);
 			nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
 			break;

Patches currently in stable-queue which might be from [email protected] are

queue-4.6/make-nfs_atomic_open-call-d_drop-on-all-open_context-errors.patch