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Subject[PATCH RFC] acpi: Fix unprotected smp_processor_id() in acpi_processor_cst_has_changed()
The acpi_processor_cst_has_changed() function is invoked from a
CPU_ONLINE or CPU_DEAD function, which might well execute on CPU 0
even though the CPU being hotplugged is some other CPU. In addition,
acpi_processor_cst_has_changed() invokes smp_processor_id() without
protection, resulting in splats when onlining CPUs.

This commit therefore changes the smp_processor_id() to pr->id, as is
used elsewhere in the code, for example, in acpi_processor_add().

This works for me, but I don't claim to understand ACPI.

Signed-off-by: Paul E. McKenney <>

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index 0e8e2de..9e57b06 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -1159,8 +1159,7 @@ int acpi_processor_cst_has_changed(struct acpi_processor *pr)
* to make the code that updates C-States be called once.

- if (smp_processor_id() == 0 &&
- cpuidle_get_driver() == &acpi_idle_driver) {
+ if (pr->id == 0 && cpuidle_get_driver() == &acpi_idle_driver) {

/* Protect against cpu-hotplug */

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