Messages in this thread | | | Date | Fri, 25 Mar 2011 20:56:43 +0100 | From | Ingo Molnar <> | Subject | Re: [tip:core/urgent] WARN_ON_SMP(): Allow use in if() statements on UP |
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* Alexey Dobriyan <adobriyan@gmail.com> wrote:
> On Fri, Mar 25, 2011 at 03:40:34PM -0400, Steven Rostedt wrote: > > On Fri, 2011-03-25 at 21:31 +0200, Alexey Dobriyan wrote: > > > > > > Would you like me to add a comment that states: > > > > > > > > /* > > > > * Use ({0;}) as just "0" will cause gcc to output: > > > > * warning: statement with no effect > > > > */ > > > > > > Try ((void)0) > > > > Maybe I should update the comment to stop further confusion: > > Ah! > > I always thought if (WARN_ON(x)) is confusing and should be banned.
I'd encourage you to read kernel/lockdep.c one day:
return DEBUG_LOCKS_WARN_ON(1); DEBUG_LOCKS_WARN_ON(1); if (DEBUG_LOCKS_WARN_ON(class->subclass != subclass)) if (DEBUG_LOCKS_WARN_ON(!irqs_disabled())) if (DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS)) if (DEBUG_LOCKS_WARN_ON(unlikely(early_boot_irqs_disabled))) if (DEBUG_LOCKS_WARN_ON(!irqs_disabled())) if (DEBUG_LOCKS_WARN_ON(current->hardirq_context)) if (DEBUG_LOCKS_WARN_ON(!irqs_disabled())) if (DEBUG_LOCKS_WARN_ON(!irqs_disabled())) if (DEBUG_LOCKS_WARN_ON(!irqs_disabled())) DEBUG_LOCKS_WARN_ON(!softirq_count()); if (DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))) if (DEBUG_LOCKS_WARN_ON(!name)) { if (DEBUG_LOCKS_WARN_ON(!key)) DEBUG_LOCKS_WARN_ON(1); if (DEBUG_LOCKS_WARN_ON(!irqs_disabled())) if (DEBUG_LOCKS_WARN_ON(depth >= MAX_LOCK_DEPTH)) if (DEBUG_LOCKS_WARN_ON(!class)) if (DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS)) if (DEBUG_LOCKS_WARN_ON(chain_key != 0)) if (DEBUG_LOCKS_WARN_ON(!irqs_disabled())) if (DEBUG_LOCKS_WARN_ON(!class)) if (DEBUG_LOCKS_WARN_ON(!hlock->nest_lock)) if (DEBUG_LOCKS_WARN_ON(!depth)) if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth)) if (DEBUG_LOCKS_WARN_ON(!depth)) if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth - 1)) if (DEBUG_LOCKS_WARN_ON(!depth && (hlock->prev_chain_key != 0))) if (DEBUG_LOCKS_WARN_ON(current->hardirqs_enabled)) { if (DEBUG_LOCKS_WARN_ON(!current->hardirqs_enabled)) { DEBUG_LOCKS_WARN_ON(current->softirqs_enabled); DEBUG_LOCKS_WARN_ON(!current->softirqs_enabled); if (DEBUG_LOCKS_WARN_ON(!depth)) if (DEBUG_LOCKS_WARN_ON(!depth))
These conditional warnings made the flow a lot clearer and simpler - while still giving us a very robust lockdep machinery that wont crash no matter what kind of anomaly happens.
But yes, i can imagine such constructs being misused as well when mixed into real, non-debug functionality. As usual, it's just a tool, with good and evil uses as well - so your 'it should be banned' position is too extreme IMHO.
Thanks,
Ingo
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