• Steven Rostedt's avatar
    bug: set warn variable before calling WARN() · dfbf2897
    Steven Rostedt authored
    This has hit me a couple of times already.  I would be debugging code
    and the system would simply hang and then reboot.  Finally, I found that
    the problem was caused by WARN_ON_ONCE() and friends.
    
    The macro WARN_ON_ONCE(condition) is defined as:
    
    	static bool __section(.data.unlikely) __warned;
    	int __ret_warn_once = !!(condition);
    
    	if (unlikely(__ret_warn_once))
    		if (WARN_ON(!__warned))
    			__warned = true;
    
    	unlikely(__ret_warn_once);
    
    Which looks great and all.  But what I have hit, is an issue when
    WARN_ON() itself hits the same WARN_ON_ONCE() code.  Because, the
    variable __warned is not yet set.  Then it too calls WARN_ON() and that
    triggers the warning again.  It keeps doing this until the stack is
    overflowed and the system crashes.
    
    By setting __warned first before calling WARN_ON() makes the original
    WARN_ON_ONCE() really only warn once, and not an infinite amount of
    times if the WARN_ON() also triggers the warning.
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    dfbf2897
bug.h 5.76 KB