> In the mips, mips64, and even the i386 arch, arch/kernel/smp.c has
> this in smp_call_function:
>
> spin_lock(&call_lock);
> call_data = &data;
>
> /* Send a message to all other CPUs and wait for them to respond */
> for (i = 0; i < smp_num_cpus; i++)
> if (i != cpu)
> core_send_ipi(i, SMP_CALL_FUNCTION);
>
> call_data isn't volatile, it's a plain static *. So how can we be sure
> that "call_data = &data" does anything other than change a register?
>
> The i386 has a wb() after the assignment; we don't even have that.
call_data is neither local nor static to the function, so the modification
of the storage location would seem to be mandatory for the compiler
before the call to core_send_ipi(), so I can see how the code, as written,
would generally work on most MIPS CPUs. However, it would be legal
for the compiler to defer the store until *just* before the invocation of
core_send_ipi(), and on moderately complex, high-ILP processors
it seems to me like the wb() might well be necessary. I take it that
you've observed a problem with this on your system?:
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