thermal_throttle_add_dev

Hello,

[13874.228704] BUG: using smp_processor_id() in preemptible [00000000] code: bash/10661
[13874.228715] caller is thermal_throttle_add_dev+0x20/0xa4
[13874.228721] Pid: 10661, comm: bash Not tainted 2.6.36-rc0-git11-07631-gfa34556-dirty #109
[13874.228725] Call Trace:
[13874.228738]  [<ffffffff811f6285>] debug_smp_processor_id+0xc9/0xe4
[13874.228744]  [<ffffffff8136ccac>] thermal_throttle_add_dev+0x20/0xa4
[13874.228750]  [<ffffffff8136cd82>] thermal_throttle_cpu_callback+0x52/0xb5
[13874.228759]  [<ffffffff81057198>] notifier_call_chain+0x32/0x5e
[13874.228767]  [<ffffffff8103c818>] ? cpu_maps_update_begin+0x12/0x14
[13874.228774]  [<ffffffff810571e3>] __raw_notifier_call_chain+0x9/0xb
[13874.228780]  [<ffffffff8103c6db>] __cpu_notify+0x1b/0x2d
[13874.228786]  [<ffffffff8136eeb2>] _cpu_up+0x6b/0xe9
[13874.228792]  [<ffffffff8136ef7a>] cpu_up+0x4a/0x57
[13874.228799]  [<ffffffff813638b7>] store_online+0x41/0x6e
[13874.228807]  [<ffffffff8129186b>] sysdev_store+0x1b/0x1d
[13874.228816]  [<ffffffff8113188e>] sysfs_write_file+0x103/0x13f
[13874.228824]  [<ffffffff810da5ff>] vfs_write+0xb1/0x14e
[13874.228830]  [<ffffffff810da898>] sys_write+0x45/0x6c
[13874.228840]  [<ffffffff81002002>] system_call_fastpath+0x16/0x1b

My first solution was quite simple - just don't use preemptible smp_processor_id().
In other words it was something like that:

--- a/arch/x86/kernel/cpu/mcheck/therm_throt.c
+++ b/arch/x86/kernel/cpu/mcheck/therm_throt.c
@@ -205,7 +205,9 @@ static int therm_throt_process(bool new_event, int event, int level)
 static __cpuinit int thermal_throttle_add_dev(struct sys_device *sys_dev)
 {
     int err;
-    struct cpuinfo_x86 *c = &cpu_data(smp_processor_id());
+    int cpu = get_cpu();
+    struct cpuinfo_x86 *c = &cpu_data(cpu);
+    put_cpu();

     err = sysfs_create_group(&sys_dev->kobj, &thermal_attr_group);
     if (err)

However, we know the exact cpu when we are about to call thermal_throttle_add_dev.
So smp_processor_id()/get_cpu() - put_cpu() is sort of redundant here. Here we are
with the second solution:

--- a/arch/x86/kernel/cpu/mcheck/therm_throt.c
+++ b/arch/x86/kernel/cpu/mcheck/therm_throt.c
@@ -202,11 +202,12 @@ static int therm_throt_process(bool new_event, int event, int level)

 #ifdef CONFIG_SYSFS
 /* Add/Remove thermal_throttle interface for CPU device: */
-static __cpuinit int thermal_throttle_add_dev(struct sys_device *sys_dev)
+static __cpuinit int thermal_throttle_add_dev(struct sys_device *sys_dev,
+                unsigned int cpu)
 {
     int err;
-    struct cpuinfo_x86 *c = &cpu_data(smp_processor_id());
-
+    struct cpuinfo_x86 *c = &cpu_data(cpu);
+   
     err = sysfs_create_group(&sys_dev->kobj, &thermal_attr_group);
     if (err)
         return err;
@@ -251,7 +252,7 @@ thermal_throttle_cpu_callback(struct notifier_block *nfb,
     case CPU_UP_PREPARE:
     case CPU_UP_PREPARE_FROZEN:
         mutex_lock(&therm_cpu_lock);
-        err = thermal_throttle_add_dev(sys_dev);
+        err = thermal_throttle_add_dev(sys_dev, cpu);
         mutex_unlock(&therm_cpu_lock);
         WARN_ON(err);
         break;
@@ -287,7 +288,7 @@ static __init int thermal_throttle_init_device(void)
 #endif
     /* connect live CPUs to sysfs */
     for_each_online_cpu(cpu) {
-        err = thermal_throttle_add_dev(get_cpu_sysdev(cpu));
+        err = thermal_throttle_add_dev(get_cpu_sysdev(cpu), cpu);
         WARN_ON(err);
     }
 #ifdef CONFIG_HOTPLUG_CPU


Good news everyone:

Subject: [tip:x86/urgent] x86, hwmon ...
Commit-ID:  51e3c1b558b31b11bf5fc66d3c6f5adacf3573f7

Thanks.


P.S. by the way:
LKML-Reference: <20100820073634.GB5209@swordfish.minsk.epam.com>

I'll ask epam for bonus... $10,000... cash. If you know what I mean. Yeah!