On Thu, 01 Mar 2007 03:34:18 -0800 Zachary Amsden <[EMAIL PROTECTED]> wrote:
> > Why is it a bug? Because there's a deadlock where this CPU is waiting for > > CPU A to take the IPI, but CPU A is waiting (with interrupts disabled) for > > this CPU to take an IPI. > > > > Then the bug is not in on_each_cpu(). It is in the usage of > clock_was_set(). For example, look at do_settimeofday in kernel/timer.c: > > write_sequnlock_irqrestore(&xtime_lock, flags); > > /* signal hrtimers about time change */ > clock_was_set(); > > return 0; Perhaps a WARN_ON(irqs_disabled()) in clock_was_set() would help. But probably the one in smp_call_function() will suffice. > And timekeeping_resume has similar code (and called from a sysdev > callback, so I don't know what the interrupt state should be ). Either > the write_sequnlock_irqrestore is redundant, and should be merely an > write_sequnlock_irq, or the callsite is not prepared to handle enabling > interrupts temporarily as must be done for on_each_cpu(), which is a > pretty scary scenario. > > What would be really, really nice would be to statically check all > callsites that issue irq disables actually keep irqs disabled. > Presumably, there was a reason they disabled irqs, and re-enabling them > underneath their noses, even if it is to avoid a race, breaks the logic > behind that reason. yup. I once played with adding warnings in places like spin_lock_irq(), but there were false positives from places which were odd-but-correct. It would be worth revisiting however. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
