nfs_atomic_open(): prevent parallel nfs_lookup() on a negative hashed

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 3d5eb5edbf509a9ebdc21878026bf26f32b8363f..19d93d0cd400f5ac175a9d257ec8a8ced0e04c21 100644 (file)
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1485,11 +1485,13 @@ int nfs_atomic_open(struct inode *dir, struct dentry *dentry,
                    struct file *file, unsigned open_flags,
                    umode_t mode, int *opened)
 {
+       DECLARE_WAIT_QUEUE_HEAD_ONSTACK(wq);
        struct nfs_open_context *ctx;
        struct dentry *res;
        struct iattr attr = { .ia_valid = ATTR_OPEN };
        struct inode *inode;
        unsigned int lookup_flags = 0;
+       bool switched = false;
        int err;
 
        /* Expect a negative dentry */
@@ -1528,6 +1530,17 @@ int nfs_atomic_open(struct inode *dir, struct dentry *dentry,
                attr.ia_size = 0;
        }
 
+       if (!(open_flags & O_CREAT) && !d_in_lookup(dentry)) {
+               d_drop(dentry);
+               switched = true;
+               dentry = d_alloc_parallel(dentry->d_parent,
+                                         &dentry->d_name, &wq);
+               if (IS_ERR(dentry))
+                       return PTR_ERR(dentry);
+               if (unlikely(!d_in_lookup(dentry)))
+                       return finish_no_open(file, dentry);
+       }
+
        ctx = create_nfs_open_context(dentry, open_flags);
        err = PTR_ERR(ctx);
        if (IS_ERR(ctx))
@@ -1563,14 +1576,23 @@ int nfs_atomic_open(struct inode *dir, struct dentry *dentry,
        trace_nfs_atomic_open_exit(dir, ctx, open_flags, err);
        put_nfs_open_context(ctx);
 out:
+       if (unlikely(switched)) {
+               d_lookup_done(dentry);
+               dput(dentry);
+       }
        return err;
 
 no_open:
        res = nfs_lookup(dir, dentry, lookup_flags);
-       err = PTR_ERR(res);
+       if (switched) {
+               d_lookup_done(dentry);
+               if (!res)
+                       res = dentry;
+               else
+                       dput(dentry);
+       }
        if (IS_ERR(res))
-               goto out;
-
+               return PTR_ERR(res);
        return finish_no_open(file, res);
 }
 EXPORT_SYMBOL_GPL(nfs_atomic_open);