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Date: Mon, 11 Aug 2008 23:46:08 -0400 (EDT)
From: Steven Rostedt <rostedt@...dmis.org>
To: Ingo Molnar <mingo@...e.hu>
cc: Huang Ying <ying.huang@...el.com>,
LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: ftrace_enabled_save/restore
Ingo,
Can you pull this into linux-tip.
Thanks,
-- Steve
On Tue, 12 Aug 2008, Huang Ying wrote:
> Hi, Steven,
>
> Below is the patch of locked ftrace_enabled_save/restore, which is based
> on the non-locked version I posted with the title:
>
> [PATCH -v3 6/7] kexec jump: __ftrace_enabled_save/restore
>
> What do you think about this?
>
> Best Regards,
> Huang Ying
> ----------------------------------------------------------->
> From: Steven Rostedt <srostedt@...hat.com>
> Subject: ftrace: cpu hotplug fix
>
> Peter Zijlstra found that taking down and bringing up a new CPU caused
> ftrace to crash the kernel. This was due to some arch calls that were
> being traced by the function tracer before the smp_processor_id was set
> up. Since the function tracer uses smp_processor_id it caused a triple
> fault.
>
> Instead of adding notrace all over the architecture code to prevent
> this problem, it is easier to simply disable the function tracer
> when bringing up a new CPU.
>
> Signed-off-by: Steven Rostedt <srostedt@...hat.com>
> Signed-off-by: Huang Ying <ying.huang@...el.com>
>
> ---
> include/linux/ftrace.h | 15 ++++++++++++---
> kernel/cpu.c | 11 ++++++++++-
> kernel/trace/ftrace.c | 20 ++++++++++++++++++++
> kernel/trace/trace_irqsoff.c | 3 +++
> kernel/trace/trace_sched_wakeup.c | 2 +-
> 5 files changed, 46 insertions(+), 5 deletions(-)
>
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -32,10 +32,19 @@ void clear_ftrace_function(void);
>
> extern void ftrace_stub(unsigned long a0, unsigned long a1);
>
> +int ftrace_enabled_save(void);
> +void ftrace_enabled_restore(int enabled);
> +
> #else /* !CONFIG_FTRACE */
> -# define register_ftrace_function(ops) do { } while (0)
> -# define unregister_ftrace_function(ops) do { } while (0)
> -# define clear_ftrace_function(ops) do { } while (0)
> +# define register_ftrace_function(ops) do { } while (0)
> +# define unregister_ftrace_function(ops) do { } while (0)
> +# define clear_ftrace_function(ops) do { } while (0)
> +# define ftrace_enabled_restore(enabled) do { } while (0)
> +
> +static inline int ftrace_enabled_save(void)
> +{
> + return 0;
> +}
> #endif /* CONFIG_FTRACE */
>
> #ifdef CONFIG_DYNAMIC_FTRACE
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -14,6 +14,7 @@
> #include <linux/kthread.h>
> #include <linux/stop_machine.h>
> #include <linux/mutex.h>
> +#include <linux/ftrace.h>
>
> /*
> * Represents all cpu's present in the system
> @@ -325,7 +326,7 @@ EXPORT_SYMBOL(cpu_down);
> /* Requires cpu_add_remove_lock to be held */
> static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
> {
> - int ret, nr_calls = 0;
> + int ret, nr_calls = 0, saved_ftrace_enabled;
> void *hcpu = (void *)(long)cpu;
> unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
>
> @@ -343,8 +344,16 @@ static int __cpuinit _cpu_up(unsigned in
> goto out_notify;
> }
>
> + /*
> + * Disable function tracing while bringing up a new CPU.
> + * We don't want to trace functions that can not handle a
> + * smp_processor_id() call.
> + */
> + saved_ftrace_enabled = ftrace_enabled_save();
> +
> /* Arch-specific enabling code. */
> ret = __cpu_up(cpu);
> + ftrace_enabled_restore(saved_ftrace_enabled);
> if (ret != 0)
> goto out_notify;
> BUG_ON(!cpu_online(cpu));
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -151,6 +151,26 @@ static int __unregister_ftrace_function(
> return ret;
> }
>
> +int ftrace_enabled_save(void)
> +{
> + mutex_lock(&ftrace_sysctl_lock);
> +
> + return __ftrace_enabled_save();
> +}
> +
> +void ftrace_enabled_restore(int enabled)
> +{
> + /* ftrace_enabled_restore must be paired with ftrace_enabled_save */
> + if (!mutex_is_locked(&ftrace_sysctl_lock)) {
> + WARN_ON(1);
> + return;
> + }
> +
> + __ftrace_enabled_restore(enabled);
> +
> + mutex_unlock(&ftrace_sysctl_lock);
> +}
> +
> #ifdef CONFIG_DYNAMIC_FTRACE
>
> static struct task_struct *ftraced_task;
> --- a/kernel/trace/trace_irqsoff.c
> +++ b/kernel/trace/trace_irqsoff.c
> @@ -76,6 +76,9 @@ irqsoff_tracer_call(unsigned long ip, un
> long disabled;
> int cpu;
>
> + if (unlikely(!ftrace_enabled))
> + return;
> +
> /*
> * Does not matter if we preempt. We test the flags
> * afterward, to see if irqs are disabled or not.
> --- a/kernel/trace/trace_sched_wakeup.c
> +++ b/kernel/trace/trace_sched_wakeup.c
> @@ -45,7 +45,7 @@ wakeup_tracer_call(unsigned long ip, uns
> int resched;
> int cpu;
>
> - if (likely(!wakeup_task))
> + if (likely(!wakeup_task) || !ftrace_enabled)
> return;
>
> resched = need_resched();
>
>
>
--
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