cope with potentially long ->d_dname() output for shmem/hugetlb

commit 118b2302 upstream.

dynamic_dname() is both too much and too little for those - the
output may be well in excess of 64 bytes dynamic_dname() assumes
to be enough (thanks to ashmem feeding really long names to
shmem_file_setup()) and vsnprintf() is an overkill for those
guys.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Colin Cross <ccross@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/dcache.c

@@ -2724,6 +2724,17 @@ char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
 	return memcpy(buffer, temp, sz);
 }
 
+char *simple_dname(struct dentry *dentry, char *buffer, int buflen)
+{
+	char *end = buffer + buflen;
+	/* these dentries are never renamed, so d_lock is not needed */
+	if (prepend(&end, &buflen, " (deleted)", 11) ||
+	    prepend_name(&end, &buflen, &dentry->d_name) ||
+	    prepend(&end, &buflen, "/", 1))
+		end = ERR_PTR(-ENAMETOOLONG);
+	return end;
+}
+
 /*
  * Write full pathname from the root of the filesystem into the buffer.
  */

fs/hugetlbfs/inode.c

@@ -916,14 +916,8 @@ static int get_hstate_idx(int page_size_log)
 	return h - hstates;
 }
 
-static char *hugetlb_dname(struct dentry *dentry, char *buffer, int buflen)
-{
-	return dynamic_dname(dentry, buffer, buflen, "/%s (deleted)",
-				dentry->d_name.name);
-}
-
 static struct dentry_operations anon_ops = {
-	.d_dname = hugetlb_dname
+	.d_dname = simple_dname
 };
 
 /*

include/linux/dcache.h

@@ -332,6 +332,7 @@ extern int d_validate(struct dentry *, struct dentry *);
  * helper function for dentry_operations.d_dname() members
  */
 extern char *dynamic_dname(struct dentry *, char *, int, const char *, ...);
+extern char *simple_dname(struct dentry *, char *, int);
 
 extern char *__d_path(const struct path *, const struct path *, char *, int);
 extern char *d_absolute_path(const struct path *, char *, int);

mm/shmem.c

@@ -2879,14 +2879,8 @@ EXPORT_SYMBOL_GPL(shmem_truncate_range);
 
 /* common code */
 
-static char *shmem_dname(struct dentry *dentry, char *buffer, int buflen)
-{
-	return dynamic_dname(dentry, buffer, buflen, "/%s (deleted)",
-				dentry->d_name.name);
-}
-
 static struct dentry_operations anon_ops = {
-	.d_dname = shmem_dname
+	.d_dname = simple_dname
 };
 
 /**