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[PATCH 3.16 237/305] make nfs_atomic_open() call d_drop() on all ->open_context() errors.

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3.16.37-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Al Viro <viro@ZenIV.linux.org.uk>

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()).

Tested-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 fs/nfs/dir.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1492,9 +1492,9 @@ 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);
 			break;
 		case -EISDIR:

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[PATCH 3.16 237/305] make nfs_atomic_open() call d_drop() on all  ->open_context() errors. Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 13:30 +0200

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