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 <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
