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Date: Thu, 11 Apr 2013 14:27:57 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: RT <linux-rt-users@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Clark Williams <clark@...hat.com>,
John Kacur <jkacur@...hat.com>,
Tony Luck <tony.luck@...el.com>,
Borislav Petkov <bp@...en8.de>,
Mauro Carvalho Chehab <mchehab@...hat.com>,
Ingo Molnar <mingo@...nel.org>,
"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [PATCH RT] x86/mce: Defer mce wakeups to threads for PREEMPT_RT
On Thu, 2013-04-11 at 14:23 -0400, Steven Rostedt wrote:
> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> index e8d8ad0..060e473 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -18,6 +18,7 @@
> #include <linux/rcupdate.h>
> #include <linux/kobject.h>
> #include <linux/uaccess.h>
> +#include <linux/kthread.h>
> #include <linux/kdebug.h>
> #include <linux/kernel.h>
> #include <linux/percpu.h>
> @@ -1308,6 +1309,61 @@ static void mce_do_trigger(struct work_struct *work)
>
> static DECLARE_WORK(mce_trigger_work, mce_do_trigger);
>
> +static void __mce_notify_work(void)
> +{
> + /* Not more than two messages every minute */
> + static DEFINE_RATELIMIT_STATE(ratelimit, 60*HZ, 2);
> +
> + /* wake processes polling /dev/mcelog */
> + wake_up_interruptible(&mce_chrdev_wait);
> +
> + /*
> + * There is no risk of missing notifications because
> + * work_pending is always cleared before the function is
> + * executed.
> + */
> + if (mce_helper[0] && !work_pending(&mce_trigger_work))
> + schedule_work(&mce_trigger_work);
> +
> + if (__ratelimit(&ratelimit))
> + pr_info(HW_ERR "Machine check events logged\n");
> +}
> +
> +#ifdef CONFIG_PREEMPT_RT_FULL
> +struct task_struct *mce_notify_helper;
> +
> +static int mce_notify_helper_thread(void *unused)
> +{
> + while (!kthread_should_stop()) {
> + __mce_notify_work();
> + set_current_state(TASK_INTERRUPTIBLE);
> + schedule();
> + }
> + return 0;
> +}
> +
> +static int mce_notify_work_init(void)
> +{
> + mce_notify_helper = kthread_create(mce_notify_helper_thread, NULL,
> + "mce-notify");
> + if (!mce_notify_helper)
> + return -ENOMEM;
> +
> + return 0;
> +}
> +
> +static void mce_notify_work()
> +{
> + wake_up_process(mce_notify_helper);
> +}
> +#else
> +static void mce_notify_work(void)
> +{
> + __mce_notify_work();
> +}
> +static inline int mce_notify_work_init(void) { return 0; }
> +#endif
> +
> /*
> * Notify the user(s) about new machine check events.
> * Can be called from interrupt context, but not from machine check/NMI
> @@ -1315,24 +1371,8 @@ static DECLARE_WORK(mce_trigger_work, mce_do_trigger);
> */
> int mce_notify_irq(void)
> {
> - /* Not more than two messages every minute */
> - static DEFINE_RATELIMIT_STATE(ratelimit, 60*HZ, 2);
> -
> if (test_and_clear_bit(0, &mce_need_notify)) {
> - /* wake processes polling /dev/mcelog */
> - wake_up_interruptible(&mce_chrdev_wait);
> -
> - /*
> - * There is no risk of missing notifications because
> - * work_pending is always cleared before the function is
> - * executed.
> - */
> - if (mce_helper[0] && !work_pending(&mce_trigger_work))
> - schedule_work(&mce_trigger_work);
> -
> - if (__ratelimit(&ratelimit))
> - pr_info(HW_ERR "Machine check events logged\n");
> -
> + mce_notify_work();
> return 1;
> }
> return 0;
> @@ -2375,6 +2415,8 @@ static __init int mcheck_init_device(void)
> /* register character device /dev/mcelog */
> misc_register(&mce_chrdev_device);
>
> + err = mce_notify_work_init();
> +
> return err;
> }
Ignore the below, I didn't realize I had other changes when I did my git
diff to make this patch :-/
-- Steve
> device_initcall_sync(mcheck_init_device);
> diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
> index 33e5d14..120c790 100644
> --- a/arch/x86/kernel/process_32.c
> +++ b/arch/x86/kernel/process_32.c
> @@ -198,34 +198,6 @@ start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)
> }
> EXPORT_SYMBOL_GPL(start_thread);
>
> -#ifdef CONFIG_PREEMPT_RT_FULL
> -static void switch_kmaps(struct task_struct *prev_p, struct task_struct *next_p)
> -{
> - int i;
> -
> - /*
> - * Clear @prev's kmap_atomic mappings
> - */
> - for (i = 0; i < prev_p->kmap_idx; i++) {
> - int idx = i + KM_TYPE_NR * smp_processor_id();
> - pte_t *ptep = kmap_pte - idx;
> -
> - kpte_clear_flush(ptep, __fix_to_virt(FIX_KMAP_BEGIN + idx));
> - }
> - /*
> - * Restore @next_p's kmap_atomic mappings
> - */
> - for (i = 0; i < next_p->kmap_idx; i++) {
> - int idx = i + KM_TYPE_NR * smp_processor_id();
> -
> - set_pte(kmap_pte - idx, next_p->kmap_pte[i]);
> - }
> -}
> -#else
> -static inline void
> -switch_kmaps(struct task_struct *prev_p, struct task_struct *next_p) { }
> -#endif
> -
>
> /*
> * switch_to(x,y) should switch tasks from x to y.
> @@ -305,7 +277,40 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
> task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT))
> __switch_to_xtra(prev_p, next_p, tss);
>
> - switch_kmaps(prev_p, next_p);
> +#ifdef CONFIG_PREEMPT_RT_FULL
> + /*
> + * Save @prev's kmap_atomic stack
> + */
> + prev_p->kmap_idx = __this_cpu_read(__kmap_atomic_idx);
> + if (unlikely(prev_p->kmap_idx)) {
> + int i;
> +
> + for (i = 0; i < prev_p->kmap_idx; i++) {
> + int idx = i + KM_TYPE_NR * smp_processor_id();
> +
> + pte_t *ptep = kmap_pte - idx;
> + prev_p->kmap_pte[i] = *ptep;
> + kpte_clear_flush(ptep, __fix_to_virt(FIX_KMAP_BEGIN + idx));
> + }
> +
> + __this_cpu_write(__kmap_atomic_idx, 0);
> + }
> +
> + /*
> + * Restore @next_p's kmap_atomic stack
> + */
> + if (unlikely(next_p->kmap_idx)) {
> + int i;
> +
> + __this_cpu_write(__kmap_atomic_idx, next_p->kmap_idx);
> +
> + for (i = 0; i < next_p->kmap_idx; i++) {
> + int idx = i + KM_TYPE_NR * smp_processor_id();
> +
> + set_pte(kmap_pte - idx, next_p->kmap_pte[i]);
> + }
> + }
> +#endif
>
> /*
> * Leave lazy mode, flushing any hypercalls made here.
>
--
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