[PATCH 6/6] kexec jump: fix for ftrace

[PATCH 6/6] kexec jump: fix for ftrace

[Huang Ying]

Restore ftrace after jumping back from kexeced kernel.

Signed-off-by: Huang Ying <ying.huang@intel.com>

---
 arch/x86/kernel/machine_kexec_32.c |   19 +++++++++++++++++++
 kernel/kexec.c                     |    2 --
 2 files changed, 19 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/machine_kexec_32.c
+++ b/arch/x86/kernel/machine_kexec_32.c
@@ -12,6 +12,7 @@
 #include <linux/init.h>
 #include <linux/numa.h>
 #include <linux/ftrace.h>
+#include <linux/suspend.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -117,6 +118,7 @@ void machine_kexec(struct kimage *image)
 {
 	unsigned long page_list[PAGES_NR];
 	void *control_page;
+	int save_ftrace_enabled;
 	asmlinkage unsigned long
 		(*relocate_kernel_ptr)(unsigned long indirection_page,
 				       unsigned long control_page,
@@ -124,7 +126,15 @@ void machine_kexec(struct kimage *image)
 				       unsigned int has_pae,
 				       unsigned int preserve_context);
 
+#ifdef CONFIG_KEXEC_JUMP
+	if (kexec_image->preserve_context)
+		save_processor_state();
+#endif
+
+#ifdef CONFIG_FTRACE
+	save_ftrace_enabled = ftrace_enabled;
 	tracer_disable();
+#endif
 
 	/* Interrupts aren't acceptable while we reboot */
 	raw_local_irq_disable();
@@ -182,6 +192,15 @@ void machine_kexec(struct kimage *image)
 					   (unsigned long)page_list,
 					   image->start, cpu_has_pae,
 					   image->preserve_context);
+
+#ifdef CONFIG_KEXEC_JUMP
+	if (kexec_image->preserve_context)
+		restore_processor_state();
+#endif
+
+#ifdef CONFIG_FTRACE
+	ftrace_enabled = save_ftrace_enabled;
+#endif
 }
 
 void arch_crash_save_vmcoreinfo(void)
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -1469,7 +1469,6 @@ int kernel_kexec(void)
 		error = device_power_down(PMSG_FREEZE);
 		if (error)
 			goto Enable_irqs;
-		save_processor_state();
 	} else
 #endif
 	{
@@ -1482,7 +1481,6 @@ int kernel_kexec(void)
 
 #ifdef CONFIG_KEXEC_JUMP
 	if (kexec_image->preserve_context) {
-		restore_processor_state();
 		device_power_up(PMSG_RESTORE);
  Enable_irqs:
 		local_irq_enable();

Re: [PATCH 6/6] kexec jump: fix for ftrace

[Pavel Machek]

> Restore ftrace after jumping back from kexeced kernel.
> 
> Signed-off-by: Huang Ying <ying.huang@intel.com>
> 
> ---
>  arch/x86/kernel/machine_kexec_32.c |   19 +++++++++++++++++++
>  kernel/kexec.c                     |    2 --
>  2 files changed, 19 insertions(+), 2 deletions(-)
> 
> @@ -124,7 +126,15 @@ void machine_kexec(struct kimage *image)
>  				       unsigned int has_pae,
>  				       unsigned int preserve_context);
>  
> +#ifdef CONFIG_KEXEC_JUMP
> +	if (kexec_image->preserve_context)
> +		save_processor_state();
> +#endif
> +
> +#ifdef CONFIG_FTRACE
> +	save_ftrace_enabled = ftrace_enabled;
>  	tracer_disable();
> +#endif
>  
>  	/* Interrupts aren't acceptable while we reboot */
>  	raw_local_irq_disable();

The patch does way more than its changelog says...
									Pavel


> @@ -182,6 +192,15 @@ void machine_kexec(struct kimage *image)
>  					   (unsigned long)page_list,
>  					   image->start, cpu_has_pae,
>  					   image->preserve_context);
> +
> +#ifdef CONFIG_KEXEC_JUMP
> +	if (kexec_image->preserve_context)
> +		restore_processor_state();
> +#endif
> +
> +#ifdef CONFIG_FTRACE
> +	ftrace_enabled = save_ftrace_enabled;
> +#endif
>  }
>  
>  void arch_crash_save_vmcoreinfo(void)
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -1469,7 +1469,6 @@ int kernel_kexec(void)
>  		error = device_power_down(PMSG_FREEZE);
>  		if (error)
>  			goto Enable_irqs;
> -		save_processor_state();
>  	} else
>  #endif
>  	{
> @@ -1482,7 +1481,6 @@ int kernel_kexec(void)
>  
>  #ifdef CONFIG_KEXEC_JUMP
>  	if (kexec_image->preserve_context) {
> -		restore_processor_state();
>  		device_power_up(PMSG_RESTORE);
>   Enable_irqs:
>  		local_irq_enable();
> 

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [PATCH 6/6] kexec jump: fix for ftrace

[Vivek Goyal]

On Thu, Aug 07, 2008 at 05:05:37PM +0800, Huang Ying wrote:
> Restore ftrace after jumping back from kexeced kernel.
> 
> Signed-off-by: Huang Ying <ying.huang@intel.com>
> 
> ---
>  arch/x86/kernel/machine_kexec_32.c |   19 +++++++++++++++++++
>  kernel/kexec.c                     |    2 --
>  2 files changed, 19 insertions(+), 2 deletions(-)
> 
> --- a/arch/x86/kernel/machine_kexec_32.c
> +++ b/arch/x86/kernel/machine_kexec_32.c
> @@ -12,6 +12,7 @@
>  #include <linux/init.h>
>  #include <linux/numa.h>
>  #include <linux/ftrace.h>
> +#include <linux/suspend.h>
>  
>  #include <asm/pgtable.h>
>  #include <asm/pgalloc.h>
> @@ -117,6 +118,7 @@ void machine_kexec(struct kimage *image)
>  {
>  	unsigned long page_list[PAGES_NR];
>  	void *control_page;
> +	int save_ftrace_enabled;
>  	asmlinkage unsigned long
>  		(*relocate_kernel_ptr)(unsigned long indirection_page,
>  				       unsigned long control_page,
> @@ -124,7 +126,15 @@ void machine_kexec(struct kimage *image)
>  				       unsigned int has_pae,
>  				       unsigned int preserve_context);
>  
> +#ifdef CONFIG_KEXEC_JUMP
> +	if (kexec_image->preserve_context)
> +		save_processor_state();
> +#endif
> +
> +#ifdef CONFIG_FTRACE
> +	save_ftrace_enabled = ftrace_enabled;
>  	tracer_disable();
> +#endif
>  
>  	/* Interrupts aren't acceptable while we reboot */
>  	raw_local_irq_disable();
> @@ -182,6 +192,15 @@ void machine_kexec(struct kimage *image)
>  					   (unsigned long)page_list,
>  					   image->start, cpu_has_pae,
>  					   image->preserve_context);
> +
> +#ifdef CONFIG_KEXEC_JUMP
> +	if (kexec_image->preserve_context)
> +		restore_processor_state();
> +#endif
> +
> +#ifdef CONFIG_FTRACE
> +	ftrace_enabled = save_ftrace_enabled;
> +#endif
>  }
>  

Hi Huang,

What kind of problem we run into if we don't disable the ftracer?

I think there are too many #ifdefs now and probably we can at least
get rid if #ifdef CONFIG_FTRACE thing.

I think ftracer needs to export the function to enable the tracer
back (tracer_enable()) so that we don't directly play with ftrace_enabled
variable. tracer_enable() can be do {} while{0} in case of CONFIG_FTRACE=n
so that we can get rid of #ifdefs here.

Thanks
Vivek

Re: [PATCH 6/6] kexec jump: fix for ftrace

[Huang Ying]

On Thu, 2008-08-07 at 09:38 -0400, Vivek Goyal wrote:
[...]
> What kind of problem we run into if we don't disable the ftracer?
> 
> I think there are too many #ifdefs now and probably we can at least
> get rid if #ifdef CONFIG_FTRACE thing.
> 
> I think ftracer needs to export the function to enable the tracer
> back (tracer_enable()) so that we don't directly play with ftrace_enabled
> variable. tracer_enable() can be do {} while{0} in case of CONFIG_FTRACE=n
> so that we can get rid of #ifdefs here.

The ftracer issue for kexec is reported by Dhaval Giani and fixed by
Ingo as in following thread:

http://lkml.org/lkml/2008/2/19/175

After some testing, I found that if we enable ftrace before
restore_processor_state(), system will hang. I think maybe ftracer
depends on some processor state that we destroyed during kexec and
restored by restore_processor_state(). So I move save_processor_state()
and restore_processor_state() into machine_kexec() and enable ftrace
after restore_processor_state().

The #ifdef CONFIG_FTRACE should be removed. I think an interface like
irq_save/restore is good for this.

saved_ftrace_enabled = ftrace_save_enabled()
<...>
ftrace_restore_enabled(saved_ftrace_enabled)

Best Regards,
Huang Ying