[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, 7 insertions, 1 deletions

diff --git a/arch/i386/kernel/mpparse.c b/arch/i386/kernel/mpparse.c
index 788efffa9930..5d0b9a8fc43d 100644
--- a/arch/i386/kernel/mpparse.c
+++ b/arch/i386/kernel/mpparse.c
@@ -122,7 +122,7 @@ static int MP_valid_apicid(int apicid, int version)
 
 static void __init MP_processor_info (struct mpc_config_processor *m)
 {
-        int ver, apicid;
+        int ver, apicid, cpu, found_bsp = 0;
         physid_mask_t tmp;
         
         if (!(m->mpc_cpuflag & CPU_ENABLED))
@@ -181,6 +181,7 @@ static void __init MP_processor_info (struct mpc_config_processor *m)
         if (m->mpc_cpuflag & CPU_BOOTPROCESSOR) {
                 Dprintk("    Bootup CPU\n");
                 boot_cpu_physical_apicid = m->mpc_apicid;
+                found_bsp = 1;
         }
 
         if (num_processors >= NR_CPUS) {
@@ -204,6 +205,11 @@ static void __init MP_processor_info (struct mpc_config_processor *m)
                 return;
         }
 
+        if (found_bsp)
+                cpu = 0;
+        else
+                cpu = num_processors - 1;
+        cpu_set(cpu, cpu_possible_map);
         tmp = apicid_to_cpu_present(apicid);
         physids_or(phys_cpu_present_map, phys_cpu_present_map, tmp);