On Tue, 2 Feb 2021 16:05:13 -0500 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > On Tue, 2 Feb 2021 19:30:34 +0100 > Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > That does mean that kprobes are then fundamentally running from > > in_nmi(), which is what started all this. > > I just thought about the fact that tracing records the context of the > function it is called in. If you set "in_nmi()" for all ftrace handlers, > then all functions will look like they are in an NMI context during tracing. > > That is, the preempt count is checked to fill in the flags in the ring > buffer that denotes what context the event (in this case the function) was > called in. Ah, that is what I worried about. ftrace and kprobes handler usually want to know "what is the actual status of the system where the probe hits". If the new kernel_exception_enter() for ftrace/kprobes or any other kernel instrumention does __preempt_count_add(KEX_OFFSET + NMI_OFFSET + HARDIRQ_OFFSET); And we can distinguish the KEX from NMI, and get the original status of the context. What would you think about? Thank you, -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
