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SubjectRe: [PATCH 0 of 9] x86/smp function calls: convert x86 tlb flushes to use function calls [POST 2]
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On Mon, 2008-08-18 at 23:18 -0700, Jeremy Fitzhardinge wrote:
> Ingo Molnar wrote:
> > * Ingo Molnar <mingo@elte.hu> wrote:
> >
> >
> >> nice stuff!
> >>
> >> I suspect the extra cost might be worth it for two reasons: 1) we
> >> could optimize the cross-call implementation further 2) on systems
> >> where TLB flushes actually matter, the ability to overlap multiple TLB
> >> flushes to the same single CPU might improve workloads.
> >>
> >> FYI, i've created a new -tip topic for your patches, tip/x86/tlbflush.
> >> It's based on tip/irq/sparseirq (there are a good deal of dependencies
> >> with that topic).
> >>
> >
> > i threw it into -tip testing for a while - triggered the lockdep warning
> > on 64-bit below.
> >
> > Ingo
> >
> > ------------>
> > checking TSC synchronization [CPU#0 -> CPU#1]: passed.
> >
> > =============================================
> > [ INFO: possible recursive locking detected ]
> > 2.6.27-rc3-tip #1
> > ---------------------------------------------
> > swapper/0 is trying to acquire lock:
> > (&call_function_queues[i].lock){....}, at: [<ffffffff8026cbba>] ipi_call_lock_irq+0x25/0x2e
> >
> > but task is already holding lock:
> > (&call_function_queues[i].lock){....}, at: [<ffffffff8026cbba>] ipi_call_lock_irq+0x25/0x2e
> >
>
> I think this might be a spurious "holding multiple locks in the same
> class" bug. All the queue locks are presumably in the same class, and
> ipi_call_lock_irq() wants to hold them all to lock out any IPIs.
> Spurious because this is the only place which holds more than one queue
> lock, and it always locks 0->N.
>
> I guess the fix is to use an outer lock and use spin_lock_nested() (now
> that it exists). Something along these lines?

spin_lock_nested() has existed for a long time, but you are now using
spin_lock_nest_lock(), which is a totally different annotation





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