Messages in this thread | | | Date | Thu, 1 Mar 2007 07:22:25 -0800 | From | Andrew Morton <> | Subject | Re: Bug in on_each_cpu? |
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On Thu, 01 Mar 2007 03:47:39 -0800 Zachary Amsden <zach@vmware.com> wrote:
> Rusty Russell wrote: > > On Thu, 2007-03-01 at 03:34 -0800, Zachary Amsden wrote: > > > >> 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. > >> > > > > For the moment, how about a BUG_ON() in on_each_cpu()? > > > > Sounds quite decent. But why does on_each_cpu need to disable > interrupts at all? It just calls func(), then re-enables interrupts. > So whatever was going to happen during func() that might not be > interrupt safe could just be done in the callee, avoiding the rather > expensive mess of disabling and re-enabling interrupts for those cases > where it doesn't matter.
The handler for smp_call_function() is called with local interrupts disabled (from the IPI handler).
So to provide a consistent call environment for that handler, on_each_cpu() will also disable local interrupts when making the direct call on this CPU.
Similarly the !CONFIG_SMP version of on_each_cpu() disables local interrupts when running the caller's function.
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