(Limitations and Known Bugs): State that the number of parens/brackets in

a k&r region is limited.

doc/misc/cc-mode.texi

@@ -6759,6 +6759,14 @@ it and font-locks it OK.  Templates used in expressions, and nested
 templates do not fare so well.  Sometimes a workaround is to refontify
 the expression after typing the closing @samp{>}.
 
+@item
+In a @dfn{k&r region} (the part of an old-fashioned C function
+declaration which specifies the types of its parameters, coming
+between the parameter list and the opening brace), there should be at
+most 20 top-level parenthesis and bracket pairs.  This limit has been
+imposed for performance reasons.  If it is violated, the source file
+might be incorrectly indented or fontified.
+
 @item
 On loading @ccmode{}, sometimes this error message appears:
 

lisp/ChangeLog

+2008-03-07  Alan Mackenzie  <acm@muc.de>
+
+	* progmodes/cc-engine.el (c-in-knr-argdecl): Limit number of
+	paren/bracket pairs parsed, to solve performance problem.
+
 2008-03-07  Bastien Guerry  <bzg@altern.org>
 
 	* bookmark.el (bookmark-set): Don't check for