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authorSteven Rostedt (Red Hat) <rostedt@goodmis.org>2014-06-25 02:58:26 +0200
committerSteven Rostedt <rostedt@goodmis.org>2014-07-17 15:45:05 +0200
commitb8f99b3e0e066e7b2f3dbc348fe33d8277950727 (patch)
tree6ab3e2db3400980c723ff5d8cf64252a7be2a2c8 /kernel/power/suspend.c
parentftrace/x86: Have function graph tracer use its own trampoline (diff)
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x86, power, suspend: Annotate restore_processor_state() with notrace
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" <rjw@rjwysocki.net> Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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