lkml.org 
[lkml]   [2016]   [Mar]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] bug: Set warn variable before calling WARN()
On Tue, Mar 01, 2016 at 11:09:39AM -0500, Steven Rostedt wrote:
> 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: Steven Rostedt <rostedt@goodmis.org>

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

\
 
 \ /
  Last update: 2016-03-01 18:21    [W:0.038 / U:1.652 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site