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SubjectRe: smp_call_function & BH handlers

In article <Pine.LNX.4.33.0111271935520.23151-100000@localhost.localdomain> Ingo Molnar wrote:

> On Tue, 27 Nov 2001, Maneesh Soni wrote:

>> I am working with Dipankar on Read-Copy Update, and experimenting with
>> smp_call_function(). We believed the comments for this routine and
>> faced this problem. That's why this question came. I have not yet
>> searched kernel sources for such places hence not sure whether there
>> are really such places or not.

> we had similar lockup problems before, eg. TLB flushes initiated from
> IRQ/BH contexts - which is illegal now. Generally it's not safe to assume
> that every CPU is responsive to synchronous events triggered from IRQ/BH
> contexts. Every read_lock user is prone to this problem.

Thanks for the clarification. Should we update the
function header for smp_call_function() to say that it is illegal
to use it from both IRQ and BH contexts ?

Along the same lines, I am wondering if nowait broadcast IPI sender
waiting for IPI handlers to start in all other CPUs is a by-product
of the implementation. I can see the need for two types of
such IPIs - 1. send the broadcast IPI and forget about it and
2. send the broadcast IPI and wait for completion of the handlers.

Is there a need for the linux kernel to have a broadcast IPI
mechanism that waits for the start of the IPI handler elsewhere but
not till the end ?

Dipankar Sarma <>
Linux Technology Center, IBM Software Lab, Bangalore, India.
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