On Fri, Jul 05, 2013 at 09:57:01PM +0530, Preeti U Murthy wrote:
> cfd->cpumask_ipi is used only in smp_call_function_many().The existing
> comment around it says that this additional mask is used because
> cfd->cpumask can get overwritten.
>
> There is no reason why the cfd->cpumask can be overwritten, since this
> is a per_cpu mask; nobody can change it but us and we are
> called with preemption disabled.
The ChangeLog for f44310b98ddb7f0d06550d73ed67df5865e3eda5
which import cfd->cpumask_ipi saied the reason why we need
it:
" As explained by Linus as well:
|
| Once we've done the "list_add_rcu()" to add it to the
| queue, we can have (another) IPI to the target CPU that can
| now see it and clear the mask.
|
| So by the time we get to actually send the IPI, the mask might
| have been cleared by another IPI.
|
This patch also fixes a system hang problem, if the data->cpumask
gets cleared after passing this point:
if (WARN_ONCE(!mask, "empty IPI mask"))
return;
then the problem in commit 83d349f35e1a ("x86: don't send an IPI to
the empty set of CPU's") will happen again.
"
So this patch is wrong.
And you should cc linus and Jan Beulich who give acked-by tag to
the commit.
Thanks.
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