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

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()).

Cc: stable@vger.kernel.org # v3.10+
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>

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 2817cce..d8015a0 100644 (file)
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1539,9 +1539,9 @@ int nfs_atomic_open(struct inode *dir, struct dentry *dentry,
                err = PTR_ERR(inode);
                trace_nfs_atomic_open_exit(dir, ctx, open_flags, err);
                put_nfs_open_context(ctx);
                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:
                switch (err) {
                case -ENOENT:

-                       d_drop(dentry);

                        d_add(dentry, NULL);
                        nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
                        break;
                        d_add(dentry, NULL);
                        nfs_set_verifier(dentry, nfs_save_change_attribute(dir));
                        break;