What's TRACE_IRQS_OFF_DEBUG for?

[Andy Lutomirski]

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.
 */
#if defined(CONFIG_DYNAMIC_FTRACE) && defined(CONFIG_TRACE_IRQFLAGS)

.macro TRACE_IRQS_OFF_DEBUG
...

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

-- 
Andy Lutomirski
AMA Capital Management, LLC
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