[PATCH] i386 boottime for_each_cpu broken

for_each_cpu walks through all processors in cpu_possible_map, which is
defined as cpu_callout_map on i386 and isn't initialised until all
processors have been booted. This breaks things which do for_each_cpu
iterations early during boot. So, define cpu_possible_map as a bitmap with
NR_CPUS bits populated. This was triggered by a patch i'm working on which
does alloc_percpu before bringing up secondary processors.

From: Alexander Nyberg <alexn@telia.com>

i386-boottime-for_each_cpu-broken.patch
i386-boottime-for_each_cpu-broken-fix.patch

The SMP version of __alloc_percpu checks the cpu_possible_map before
allocating memory for a certain cpu.  With the above patches the BSP cpuid
is never set in cpu_possible_map which breaks CONFIG_SMP on uniprocessor
machines (as soon as someone tries to dereference something allocated via
__alloc_percpu, which in fact is never allocated since the cpu is not set
in cpu_possible_map).

Signed-off-by: Zwane Mwaikambo <zwane@arm.linux.org.uk>
Signed-off-by: Alexander Nyberg <alexn@telia.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/i386/kernel/smpboot.c b/arch/i386/kernel/smpboot.c
index 8e950cdff1a0..5e4893d2b9f2 100644
--- a/arch/i386/kernel/smpboot.c
+++ b/arch/i386/kernel/smpboot.c
@@ -88,6 +88,8 @@ EXPORT_SYMBOL(cpu_online_map);
 cpumask_t cpu_callin_map;
 cpumask_t cpu_callout_map;
 EXPORT_SYMBOL(cpu_callout_map);
+cpumask_t cpu_possible_map;
+EXPORT_SYMBOL(cpu_possible_map);
 static cpumask_t smp_commenced_mask;
 
 /* TSC's upper 32 bits can't be written in eariler CPU (before prescott), there
@@ -1265,6 +1267,7 @@ void __devinit smp_prepare_boot_cpu(void)
         cpu_set(smp_processor_id(), cpu_online_map);
         cpu_set(smp_processor_id(), cpu_callout_map);
         cpu_set(smp_processor_id(), cpu_present_map);
+        cpu_set(smp_processor_id(), cpu_possible_map);
         per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE;
 }