[RFA][PATCH 01/27] x86, power, suspend: Annotate restore_processor_state() with notrace

[Steven Rostedt]

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>
---
 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);
 }
-- 
2.0.0


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