proc: do translation + unlink atomically at remove_proc_entry()

remove_proc_entry() does

	lock
	lookup parent
	unlock
	lock
	unlink proc entry from lists
	unlock

which can be made bit more correct by doing parent translation + unlink
without dropping lock.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/generic.c

@@ -291,19 +291,17 @@ static const struct inode_operations proc_file_inode_operations = {
  * returns the struct proc_dir_entry for "/proc/tty/driver", and
  * returns "serial" in residual.
  */
-static int xlate_proc_name(const char *name,
-			   struct proc_dir_entry **ret, const char **residual)
+static int __xlate_proc_name(const char *name, struct proc_dir_entry **ret,
+			     const char **residual)
 {
 	const char     		*cp = name, *next;
 	struct proc_dir_entry	*de;
 	int			len;
-	int 			rtn = 0;
 
 	de = *ret;
 	if (!de)
 		de = &proc_root;
 
-	spin_lock(&proc_subdir_lock);
 	while (1) {
 		next = strchr(cp, '/');
 		if (!next)
@@ -314,17 +312,24 @@ static int xlate_proc_name(const char *name,
 			if (proc_match(len, cp, de))
 				break;
 		}
-		if (!de) {
-			rtn = -ENOENT;
-			goto out;
-		}
+		if (!de)
+			return -ENOENT;
 		cp += len + 1;
 	}
 	*residual = cp;
 	*ret = de;
-out:
+	return 0;
+}
+
+static int xlate_proc_name(const char *name, struct proc_dir_entry **ret,
+			   const char **residual)
+{
+	int rv;
+
+	spin_lock(&proc_subdir_lock);
+	rv = __xlate_proc_name(name, ret, residual);
 	spin_unlock(&proc_subdir_lock);
-	return rtn;
+	return rv;
 }
 
 static DEFINE_IDA(proc_inum_ida);
@@ -797,11 +802,13 @@ void remove_proc_entry(const char *name, struct proc_dir_entry *parent)
 	const char *fn = name;
 	int len;
 
-	if (xlate_proc_name(name, &parent, &fn) != 0)
+	spin_lock(&proc_subdir_lock);
+	if (__xlate_proc_name(name, &parent, &fn) != 0) {
+		spin_unlock(&proc_subdir_lock);
 		return;
+	}
 	len = strlen(fn);
 
-	spin_lock(&proc_subdir_lock);
 	for (p = &parent->subdir; *p; p=&(*p)->next ) {
 		if (proc_match(len, fn, *p)) {
 			de = *p;