[patch] i386/x86_64: ACPI cpu_idle_wait() fix

[Ingo Molnar <mingo@elte.hu>]

Subject: [patch] i386/x86_64: ACPI cpu_idle_wait() fix
From: Ingo Molnar <mingo@elte.hu>

The scheduler on Andreas Friedrich's hyperthreading system
stopped working properly as of 2.6.18: the scheduler would
never move tasks to another CPU!

after a couple of attempts to corner the bug, the following
smoking gun was found:

BIOS reported wrong ACPI idfor the processor
CPU#1: set_cpus_allowed(), swapper:1, 3 -> 2
 [<c0103bbe>] show_trace_log_lvl+0x34/0x4a
 [<c0103ceb>] show_trace+0x2c/0x2e
 [<c01045f8>] dump_stack+0x2b/0x2d
 [<c0116a77>] set_cpus_allowed+0x52/0xec
 [<c0101d86>] cpu_idle_wait+0x2e/0x100
 [<c0259c57>] acpi_processor_power_exit+0x45/0x58
 [<c0259752>] acpi_processor_remove+0x46/0xea
 [<c025c6fb>] acpi_start_single_object+0x47/0x54
 [<c025cee5>] acpi_bus_register_driver+0xa4/0xd3
 [<c04ab2d7>] acpi_processor_init+0x57/0x77
 [<c01004d7>] init+0x146/0x2fd
 [<c0103a87>] kernel_thread_helper+0x7/0x10

a quick look at cpu_idle_wait() shows how broken that code is
on i386: it changes the init task's affinity map but never
restores it ...

and because all userspace tasks get forked by init, they all
inherited that single-CPU affinity mask. x86_64 cloned this
bug too.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 arch/i386/kernel/process.c   |    4 +++-
 arch/x86_64/kernel/process.c |    4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

Index: linux/arch/i386/kernel/process.c
===================================================================
--- linux.orig/arch/i386/kernel/process.c
+++ linux/arch/i386/kernel/process.c
@@ -205,7 +205,7 @@ void cpu_idle(void)
 void cpu_idle_wait(void)
 {
 	unsigned int cpu, this_cpu = get_cpu();
-	cpumask_t map;
+	cpumask_t map, tmp = current->cpus_allowed;
 
 	set_cpus_allowed(current, cpumask_of_cpu(this_cpu));
 	put_cpu();
@@ -227,6 +227,8 @@ void cpu_idle_wait(void)
 		}
 		cpus_and(map, map, cpu_online_map);
 	} while (!cpus_empty(map));
+
+	set_cpus_allowed(current, tmp);
 }
 EXPORT_SYMBOL_GPL(cpu_idle_wait);
 
Index: linux/arch/x86_64/kernel/process.c
===================================================================
--- linux.orig/arch/x86_64/kernel/process.c
+++ linux/arch/x86_64/kernel/process.c
@@ -144,7 +144,7 @@ static void poll_idle (void)
 void cpu_idle_wait(void)
 {
 	unsigned int cpu, this_cpu = get_cpu();
-	cpumask_t map;
+	cpumask_t map, tmp = current->cpus_allowed;
 
 	set_cpus_allowed(current, cpumask_of_cpu(this_cpu));
 	put_cpu();
@@ -167,6 +167,8 @@ void cpu_idle_wait(void)
 		}
 		cpus_and(map, map, cpu_online_map);
 	} while (!cpus_empty(map));
+
+	set_cpus_allowed(current, tmp);
 }
 EXPORT_SYMBOL_GPL(cpu_idle_wait);