From: Eric Dumazet Now CONFIG_DEBUG_INITDATA is in, initial percpu data [__per_cpu_start,__per_cpu_end] can be declared as a redzone, and invalid accesses after boot can be detected, at least for i386. We can let non possible cpus percpu data point to this 'redzone' instead of NULL . NULL was not a good choice because part of [0..32768] memory may be readable and invalid accesses may happen unnoticed. If CONFIG_DEBUG_INITDATA is not defined, each non possible cpu points to the initial percpu data (__per_cpu_offset[cpu] == 0), thus invalid accesses wont be detected/crash. This patch also moves __per_cpu_offset[] to read_mostly area to avoid false sharing. Signed-off-by: Eric Dumazet Signed-off-by: Andrew Morton --- init/main.c | 8 ++------ 1 files changed, 2 insertions(+), 6 deletions(-) diff -puN init/main.c~__generic_per_cpu-changes init/main.c --- 25/init/main.c~__generic_per_cpu-changes Thu Feb 2 15:20:03 2006 +++ 25-akpm/init/main.c Thu Feb 2 15:20:03 2006 @@ -325,7 +325,7 @@ static inline void smp_prepare_cpus(unsi #else #ifdef __GENERIC_PER_CPU -unsigned long __per_cpu_offset[NR_CPUS]; +unsigned long __per_cpu_offset[NR_CPUS] __read_mostly; EXPORT_SYMBOL(__per_cpu_offset); @@ -343,11 +343,7 @@ static void __init setup_per_cpu_areas(v #endif ptr = alloc_bootmem(size * nr_possible_cpus); - for (i = 0; i < NR_CPUS; i++) { - if (!cpu_possible(i)) { - __per_cpu_offset[i] = (char*)0 - __per_cpu_start; - continue; - } + for_each_cpu(i) { __per_cpu_offset[i] = ptr - __per_cpu_start; memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start); ptr += size; _