On Tue, Sep 02, 2008 at 05:16:30PM -0700, David Miller wrote: > From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> > Date: Sun, 31 Aug 2008 10:33:49 -0700 > > > Make sparc64 refrain from clearing a given to-be-offlined CPU's bit in the > > cpu_online_mask until it has processed pending irqs. This change > > prevents other CPUs from being blindsided by an apparently offline CPU > > nevertheless changing globally visible state. > > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > > I wonder what the 'call_lock' thing protects :-) I didn't look till now. ;-) > That lock is a cobweb from the sparc64 code before I switched it over > to use the generic smp_call_function() code in kernel/smp.c > > So this lock doesn't protect anything any more. It is a static defined in arch/sparc64/kernel/smp.c, and is used only when setting and clearing bits in cpu_online_mask. > kernel/smp.c has a call_function_lock, which isn't marked static > but isn't declared in any header file. It is exported via ipi_call_lock(), ipi_call_unlock(), and friends. A few architectures use it to exclude some of the IPI code while setting (but not clearing) bits in cpu_online_map. These particular architectures have a phase during CPU offlining where they drain pending interrupts, so perhaps that is why they only worry about onlining? > My instinct is that the intention is that I could use this lock > for the synchronization previously provided by sparc64's local > "call_lock", and it even seems the author of kernel/smp.c intended > this kind of usage. > > Anyways, if this code is still using the worthless call_lock, it > isn't protecting against anything. Agreed. > So I'd like to hold off on this patch until this locking issue is > resolved. OK, it is your architecture. But in the meantime, sparc64 can take interrupts on CPUs whose cpu_online_map bits have been cleared. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
