Messages in this thread | | | Subject | Re: [RFC PATCH] x86/syscalls: allow tracing of __do_sys_[syscall] functions | From | Nadav Amit <> | Date | Tue, 20 Sep 2022 18:31:24 -0700 |
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Just following my questions with the answers I figured out, just to save others time.
On Sep 20, 2022, at 9:48 AM, Nadav Amit <nadav.amit@gmail.com> wrote:
> On Sep 20, 2022, at 4:02 AM, Peter Zijlstra <peterz@infradead.org> wrote: > >> On Mon, Sep 19, 2022 at 07:35:42PM -0700, Nadav Amit wrote: >> >>> 1. What is the reason that inline functions are marked with notrace? >> >> IIRC the concern is that a notrace function using an inline function; >> GCC deciding to not inline and then still hitting tracing. >> >> For noinstr we've mandated __always_inline to avoid this problem. The >> direct advantage is that those inlined into instrumented code get, well, >> instrumented.
Commit 45959ee7aa645 (“ftrace: Do not function trace inlined functions”) gives two reasons which correspond with what you were saying: (1) consistency and (2) function that should not be traced are mostly marked as inline.
I am not sure I fully agree with the arguments, specifically the consistency (any function might be inlined and not traceable). But I am too afraid/lazy to cause damage and fix it. I will remove the inline and play a bit with the kernel to see how it behaves.
>>> 2. Is probing function that is called from do_idle() supposed to work, or >>> should the kernel prevent it? >> >> Should work for some :-) Specifically it doesn't work for those that >> disable RCU, and that's (largely) being fixed here: >> >> https://lore.kernel.org/all/20220919095939.761690562@infradead.org/T/#u >> >> Although looking at it just now, I think I missed a spot.. lemme go fix >> ;-)
I did not try your patches, but I do think I figured out what’s wrong and sent a patch.
https://lore.kernel.org/lkml/EECE6FD7-FC3D-40E2-A957-151A1BE2B2F9@vmware.com/T/#t
Thanks again, Nadav
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