Re: [PATCH] [19/58] x86_64: Don't use softirq save locks in smp_call_function

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On 7/19/07, Andi Kleen <[email protected]> wrote:

It is not fully softirq safe anyways.

Ack

[ sorry, I remember having promised to send such a patch myself
some time ago, but just forgot about it ... ]

Can't do a WARN_ON unfortunately because it could trigger in the
panic case.

But this is not true at all. This function doesn't come anywhere
on the panic codepath.

+++ linux/arch/x86_64/kernel/smp.c
@@ -386,9 +386,9 @@ int smp_call_function_single (int cpu, v
                return 0;
        }

So I'd say we do need a:

WARN_ON(irqs_disabled() || in_interrupt());

or something right about here ...

-       spin_lock_bh(&call_lock);
+       spin_lock(&call_lock);
        __smp_call_function_single(cpu, func, info, nonatomic, wait);
-       spin_unlock_bh(&call_lock);
+       spin_unlock(&call_lock);
        put_cpu();
        return 0;
 }

And oh, by the way, you can safely go ahead and put that warning
in smp_call_function() *also*.

Note that panic() -> smp_send_stop() -> calls into the lower-level
__smp_call_function() directly.

So neither smp_call_function() nor smp_call_function_single() come
in the panic codepath -- the warnings there would be okay.

Satyam
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