From: Andy Lutomirski
Date: Fri Nov 06 2015 - 02:24:48 EST

The comment says:

* When dynamic function tracer is enabled it will add a breakpoint
* to all locations that it is about to modify, sync CPUs, update
* all the code, sync CPUs, then remove the breakpoints. In this time
* if lockdep is enabled, it might jump back into the debug handler
* outside the updating of the IST protection. (TRACE_IRQS_ON/OFF).
* We need to change the IDT table before calling TRACE_IRQS_ON/OFF to
* make sure the stack pointer does not get reset back to the top
* of the debug stack, and instead just reuses the current stack.


Unless I'm missing something, TRACE_IRQS_OFF isn't a tracepoint at
all, though -- it's a lockdep debugging thing. Is the worry that
someone might stick a kprobe or similar in the trace_hardirqs_off
code? If so, could we just disable that instead?

I could easily be missing something here.


Andy Lutomirski
AMA Capital Management, LLC
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