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SubjectRe: mmotm 2009-04-10-02-21 uploaded - forkbombed by work_for_cpu
On Mon, 13 Apr 2009 16:50:45 -0700 (PDT) Linus Torvalds <torvalds@linux-foundation.org> wrote:

>
>
> So I applied this (commit 01599fca6758d2cd133e78f87426fc851c9ea725:
> "cpufreq: use smp_call_function_[single|many]() in acpi-cpufreq.c"), but
> just realized - because of a compiler warning - that this looks
> suspicious:
>
> On Mon, 13 Apr 2009, Andrew Morton wrote:
> > @@ -283,7 +280,7 @@ static unsigned int get_measured_perf(st
> > unsigned int perf_percent;
> > unsigned int retval;
> >
> > - if (!work_on_cpu(cpu, read_measured_perf_ctrs, &readin))
> > + if (smp_call_function_single(cpu, read_measured_perf_ctrs, &cur, 1))
> > return 0;
> >
> > cur.aperf.whole = readin.aperf.whole -
>
> How and why did that "read_measured_perf_ctrs, &readin" become
> "read_measured_perf_ctrs, &cur" when the work_on_cpu() was converted to
> "smp_call_function_single()"?
>
> Looks like a bug. But such an odd one that I wonder whether there was some
> thought behind it? Andrew?
>

<scratches head>

OK, the acpi tree went and had conflicting changes merged into it after
I'd written the patch:

@@ -281,52 +279,57 @@ static long read_measured_perf_ctrs(void
static unsigned int get_measured_perf(struct cpufreq_policy *policy,
unsigned int cpu)
{
- struct perf_cur cur;
+ struct perf_pair readin, cur;
unsigned int perf_percent;
unsigned int retval;
- if (!work_on_cpu(cpu, read_measured_perf_ctrs, &cur))
+ if (!work_on_cpu(cpu, read_measured_perf_ctrs, &readin))
return 0;
+ cur.aperf.whole = readin.aperf.whole -
+ per_cpu(drv_data, cpu)->saved_aperf;
+ cur.mperf.whole = readin.mperf.whole -
+ per_cpu(drv_data, cpu)->saved_mperf;
+ per_cpu(drv_data, cpu)->saved_aperf = readin.aperf.whole;
+ per_cpu(drv_data, cpu)->saved_mperf = readin.mperf.whole;
+

and it appears that I incorrectly reverted part of
18b2646fe3babeb40b34a0c1751e0bf5adfdc64c while fixing the resulting
rejects.

Switching it to `readin' looks correct.


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