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 09:48:10 -0700 |
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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.
I fully understand the __always_inline. I do not understand the inline, which is a hint. Anyhow, I just thought that you would probably know, but I’ll do the digging and look at the tables to see how they look with and without inline implying notrace.
> >> 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 > ;-) >
Thank you. I’ll give it a spin as soon as I finish some stuff (which can be days).
> I'm failing to find this callchain; where is > tick_nohz_get_sleep_length() calling to elfcorehdr_read() ?!?
Very strange. According to DWARF and disassembly, the call in the code is actually to hrtimer_next_event_without() and nothing more, and elfcorehdr_read+0x40/0x40 is actually after the ret.
The strangest part is that I actually collected additional similar crashes, and I only now notice that all of them have elfcorehdr_read(). Good catch! (which makes no sense)…
I’ll move to a newer kernel, apply your patches and dig into it too.
Thanks again, Nadav
>> [ 2381.892478] elfcorehdr_read+0x40/0x40 >> [ 2381.896681] tick_nohz_get_sleep_length+0x9d/0xc0 >> [ 2381.901955] menu_select+0x4bb/0x630 >> [ 2381.905965] cpuidle_select+0x16/0x20 >> [ 2381.910069] do_idle+0x1d2/0x270 >> [ 2381.913689] cpu_startup_entry+0x20/0x30 >> [ 2381.918086] start_secondary+0x118/0x150 >> [ 2381.922484] secondary_startup_64_no_verify+0xc3/0xcb >> [ 2381.928147] </TASK> >> [ 2381.931535] Modules linked in: zram >> [ 2381.936365] CR2: ffffc90077cb6e4b >> [ 2381.940998] ---[ end trace 0000000000000000 ]—
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