Messages in this thread | | | Date | Tue, 10 Feb 2009 13:23:32 +0100 | From | Ingo Molnar <> | Subject | Re: The mysterious case of struct irqaction's mask field. |
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* Rusty Russell <rusty@rustcorp.com.au> wrote:
> Hi all, > > As part of the cpumask conversion, I came across struct irqaction: > > struct irqaction { > irq_handler_t handler; > unsigned long flags; > cpumask_t mask; > ... > }; > > Most people have been setting 'mask' to CPU_MASK_NONE, and I wondered if that > really meant that they never want this action performed on any CPU. > > But I couldn't find anyone who actually *reads* the 'mask' field. Tracing > back, it was converted from an unsigned long to a cpumask_t by wli around > 2.6.7 ("as it was intended to be"). But that conversion didn't reveal anyone > actually using the field either. > > At one point, sparc64 seems to have overloaded it for some kind of irq bucket > scheme. > > Finally, I tracked it back to the creation of (then per-arch) struct irqaction > in 1.1.82, and this hunk from linux/arch/i386/kernel/irq.c: > > @@ -12,14 +12,7 @@ > > /* > * IRQ's are in fact implemented a bit like signal handlers for the kernel. > - * The same sigaction struct is used, and with similar semantics (ie there > - * is a SA_INTERRUPT flag etc). Naturally it's not a 1:1 relation, but there > - * are similarities. > - * > - * sa_handler(int irq_NR) is the default function called (0 if no). > - * sa_mask is horribly ugly (I won't even mention it) > - * sa_flags contains various info: SA_INTERRUPT etc > - * sa_restorer is the unused > + * Naturally it's not a 1:1 relation, but there are similarities. > */ > > #include <linux/ptrace.h> > > So, it was never a cpumask at all; just a remanent of the use of sigaction for > interrupt handlers. We've been happily setting it throughout the kernel since > 1995.
Hehe, nice one :-)
> On the assumption that it has failed to coerce the spirits of our ancestors to > land among us, I'll create a patch to remove it.
Please do.
This seems to be a classic symptom of write-mostly kernel source code :-/
Ingo
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