On Thursday, June 26, 2014 12:52:22 PM Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx>
>
> ftrace_stop() is used to stop function tracing during suspend and resume
> which removes a lot of possible debugging opportunities with tracing.
> The reason was that some function in the resume path was causing a triple
> fault if it were to be traced. The issue I found was that doing something
> as simple as calling smp_processor_id() would reboot the box!
>
> When function tracing was first created I didn't have a good way to figure
> out what function was having issues, or it looked to be multiple ones. To
> fix it, we just created a big hammer approach to the problem which was to
> add a flag in the mcount trampoline that could be checked and not call
> the traced functions.
>
> Lately I developed better ways to find problem functions and I can bisect
> down to see what function is causing the issue. I removed the flag that
> stopped tracing and proceeded to find the problem function and it ended
> up being restore_processor_state(). This function makes sense as when the
> CPU comes back online from a suspend it calls this function to set up
> registers, amongst them the GS register, which stores things such as
> what CPU the processor is (if you call smp_processor_id() without this
> set up properly, it would fault).
>
> By making restore_processor_state() notrace, the system can suspend and
> resume without the need of the big hammer tracing to stop.
>
> Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
ACK
> ---
> arch/x86/power/cpu.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
> index 424f4c97a44d..6ec7910f59bf 100644
> --- a/arch/x86/power/cpu.c
> +++ b/arch/x86/power/cpu.c
> @@ -165,7 +165,7 @@ static void fix_processor_context(void)
> * by __save_processor_state()
> * @ctxt - structure to load the registers contents from
> */
> -static void __restore_processor_state(struct saved_context *ctxt)
> +static void notrace __restore_processor_state(struct saved_context *ctxt)
> {
> if (ctxt->misc_enable_saved)
> wrmsrl(MSR_IA32_MISC_ENABLE, ctxt->misc_enable);
> @@ -239,7 +239,7 @@ static void __restore_processor_state(struct saved_context *ctxt)
> }
>
> /* Needed by apm.c */
> -void restore_processor_state(void)
> +void notrace restore_processor_state(void)
> {
> __restore_processor_state(&saved_context);
> }
>
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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