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Subject[PATCH] Fix hotplug cpu on x86_64
Brian Gerst wrote:
> Brian Gerst wrote:
>> I've been seeing bogus values from /proc/loadavg on an x86-64 SMP
>> kernel (but not UP).
>>
>> $ cat /proc/loadavg
>> -1012098.26 922203.26 -982431.60 1/112 2688
>>
>> This is in the current git tree. I'm also seeing strange values in
>> /proc/stat:
>>
>> cpu 2489 40 920 60530 9398 171 288 1844674407350
>> cpu0 2509 60 940 60550 9418 191 308 0
>>
>> The first line is the sum of all cpus (I only have one), so it's
>> picking up up bad data from the non-present cpus. The last value,
>> stolen time, is completely bogus since that value is only ever used on
>> s390.
>>
>> It looks to me like there is some problem with how the per-cpu
>> structures are being initialized, or are getting corrupted. I have
>> not been able to test i386 SMP yet to see if the problem is x86_64
>> specific.
>
> I found the culprit: CPU hotplug. The problem is that
> prefill_possible_map() is called after setup_per_cpu_areas(). This
> leaves the per-cpu data sections for the future cpus uninitialized
> (still pointing to the original per-cpu data, which is initmem). Since
> the cpus exists in cpu_possible_map, for_each_cpu will iterate over them
> even though the per-cpu data is invalid.

Initialize cpu_possible_map properly in the hotplug cpu case. Before
this, the map was filled in after the per-cpu areas were set up. This
left those cpus pointing to initmem and causing invalid data in
/proc/stat and elsewhere.

Signed-off-by: Brian Gerst <bgerst@didntduck.org>
Subject: [PATCH] Fix hotplug cpu on x86_64

Initialize cpu_possible_map properly in the hotplug cpu case. Before
this, the map was filled in after the per-cpu areas were set up. This left
those cpus pointing to initmem and causing invalid data in /proc/stat and
elsewhere.

Signed-off-by: Brian Gerst <bgerst@didntduck.org>

---

arch/x86_64/kernel/smpboot.c | 41 ++++++++++++++++-------------------------
1 files changed, 16 insertions(+), 25 deletions(-)

12027fcffd85447f0fbf28264c5ee072715c345b
diff --git a/arch/x86_64/kernel/smpboot.c b/arch/x86_64/kernel/smpboot.c
--- a/arch/x86_64/kernel/smpboot.c
+++ b/arch/x86_64/kernel/smpboot.c
@@ -80,7 +80,23 @@ EXPORT_SYMBOL(cpu_online_map);
cpumask_t cpu_callin_map;
cpumask_t cpu_callout_map;

+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * cpu_possible_map should be static, it cannot change as cpu's
+ * are onlined, or offlined. The reason is per-cpu data-structures
+ * are allocated by some modules at init time, and dont expect to
+ * do this dynamically on cpu arrival/departure.
+ * cpu_present_map on the other hand can change dynamically.
+ * In case when cpu_hotplug is not compiled, then we resort to current
+ * behaviour, which is cpu_possible == cpu_present.
+ * If cpu-hotplug is supported, then we need to preallocate for all
+ * those NR_CPUS, hence cpu_possible_map represents entire NR_CPUS range.
+ * - Ashok Raj
+ */
+cpumask_t cpu_possible_map = CPU_MASK_ALL;
+#else
cpumask_t cpu_possible_map;
+#endif
EXPORT_SYMBOL(cpu_possible_map);

/* Per CPU bogomips and other parameters */
@@ -879,27 +895,6 @@ static __init void disable_smp(void)
cpu_set(0, cpu_core_map[0]);
}

-#ifdef CONFIG_HOTPLUG_CPU
-/*
- * cpu_possible_map should be static, it cannot change as cpu's
- * are onlined, or offlined. The reason is per-cpu data-structures
- * are allocated by some modules at init time, and dont expect to
- * do this dynamically on cpu arrival/departure.
- * cpu_present_map on the other hand can change dynamically.
- * In case when cpu_hotplug is not compiled, then we resort to current
- * behaviour, which is cpu_possible == cpu_present.
- * If cpu-hotplug is supported, then we need to preallocate for all
- * those NR_CPUS, hence cpu_possible_map represents entire NR_CPUS range.
- * - Ashok Raj
- */
-static void prefill_possible_map(void)
-{
- int i;
- for (i = 0; i < NR_CPUS; i++)
- cpu_set(i, cpu_possible_map);
-}
-#endif
-
/*
* Various sanity checks.
*/
@@ -967,10 +962,6 @@ void __init smp_prepare_cpus(unsigned in
current_cpu_data = boot_cpu_data;
current_thread_info()->cpu = 0; /* needed? */

-#ifdef CONFIG_HOTPLUG_CPU
- prefill_possible_map();
-#endif
-
if (smp_sanity_check(max_cpus) < 0) {
printk(KERN_INFO "SMP disabled\n");
disable_smp();
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