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


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