On Thu, 27 Mar 2003, David S. Miller wrote: > > Further more, holding a lock_irq doesn't mean bottom halves are disabled > too, it just means interrupts are disabled and no *new* softirq can be > queued. Consider the following situation: > > I think local_bh_enable() should check irqs_disabled() and honour that. > What you are showing here, that BH's can run via local_bh_enable() > even when IRQs are disabled, is a BUG(). I'd disagree. I do agree that we should obviously not run bottom halves with interrupts disabled, but I think the _real_ bug is doing "local_bh_enable()" in the first place. It's a nesting bug: you must nest the "stronger" lock inside the weaker one, which means that the following is right: local_bh_disable() .. local_irq_disable() ... local_irq_enable() .. local_bh_enable() and this is WRONG: local_irq_disable() (or spinlock) .. local_bh_disable() .. local_bh_enable() !BUG BUG BUG! .. local_irq_enable() So the bug is, in my opinion, not in BK handling, but in the caller. I missed the start of this thread, so I don't know how hard this is to fix. But if you have a buggy sequence, the _simple_ fix may be to do somehting like this: +++ local_bh_disable() local_irq_disable() (or spinlock) .. local_bh_disable() .. local_bh_enable() ! now it's a no-op and no longer a bug .. local_irq_enable() +++ local_bh_enable() What's the code sequence? Linus - : send the line "unsubscribe linux-net" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
