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Subject[PATCH -v2] cpufreq: fix racing between acpi_cpufreq_loading
Date
There is racing in
__acpi_processor_start
==> acpi_processor_load_module
==> request_module_nowait/requested = 1
before first pr path to have requested set, second cpu would request again.
that will cause acpi_cpufreq_early_init to be called in parallel,
that will cause data curruption in acpi_cpufreq_early_init...
and intermittent crash.

So add mutex to protect it.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>

---
drivers/acpi/processor_perflib.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

Index: linux-2.6/drivers/acpi/processor_perflib.c
===================================================================
--- linux-2.6.orig/drivers/acpi/processor_perflib.c
+++ linux-2.6/drivers/acpi/processor_perflib.c
@@ -235,6 +235,7 @@ void acpi_processor_ppc_exit(void)
acpi_processor_ppc_status &= ~PPC_REGISTERED;
}

+static DEFINE_MUTEX(acpi_cpufreq_load_lock);
/*
* Do a quick check if the systems looks like it should use ACPI
* cpufreq. We look at a _PCT method being available, but don't
@@ -246,8 +247,12 @@ void acpi_processor_load_module(struct a
acpi_status status = 0;
struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };

- if (!arch_has_acpi_pdc() || requested)
+ mutex_lock(&acpi_cpufreq_load_lock);
+ if (!arch_has_acpi_pdc() || requested) {
+ mutex_unlock(&acpi_cpufreq_load_lock);
return;
+ }
+
status = acpi_evaluate_object(pr->handle, "_PCT", NULL, &buffer);
if (!ACPI_FAILURE(status)) {
printk(KERN_INFO PREFIX "Requesting acpi_cpufreq\n");
@@ -255,6 +260,7 @@ void acpi_processor_load_module(struct a
requested = 1;
}
kfree(buffer.pointer);
+ mutex_unlock(&acpi_cpufreq_load_lock);
}

static int acpi_processor_get_performance_control(struct acpi_processor *pr)

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