From: "Steven Rostedt (Red Hat)" 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. Link: http://lkml.kernel.org/r/3577662.BSnUZfboWb@vostro.rjw.lan Acked-by: "Rafael J. Wysocki" Reviewed-by: Masami Hiramatsu Signed-off-by: Steven Rostedt --- 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); } -- 2.0.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/