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SubjectRe: smp_call_function_single with wait=0 considered harmful
On Wed, Dec 4, 2013 at 9:46 AM, Christoph Hellwig <> wrote:
> While doing my recent work on the generic smp function calls I noticed
> that smp_call_function_single without the wait flag can't work, as
> it allocates struct call_single_data on stack, and without the wait
> flag will happily return before the IPI has been executed.

I don't understand the problem yet. With wait==0,
smp_call_function_single() sets "csd = &__get_cpu_var(csd_data)", so
it's not using a struct on the stack. We'll queue up "func" and
likely will return before it is executed, but that should be fine
because nobody will overwrite csd_data until it *is* executed and
csd_unlock() has been called.

> This affects the following callers:
> arch/ia64/kernel/mca.c:mca_cpu_callback()
> arch/ia64/kernel/smpboot.c:ia64_sync_itc()
> arch/x86/kernel/kvm.c:kvm_cpu_notify()
> arch/x86/oprofile/nmi_int.c:oprofile_cpu_notifier()
> arch/x86/pci/amd_bus.c:amd_cpu_notify()

I don't see any reason why amd_cpu_notify() needs to use wait==0.

> drivers/staging/octeon/ethernet-rx.c:cvm_oct_enable_one_cpu()
> kernel/stop_machine.c:stop_two_cpus()
> It would be good to get these fixed so that we could remove the
> parameter. Either convert them to wait, or use a preallocated
> call_single_data and __smp_call_function_single.
> After that I'd like to remove the wait argument to prevent further
> abuses.

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