Re: [RFC PATCH v2 0/8] fprobe: Introduce fprobe function entry/exit probe

Masami Hiramatsu
2022-01-18T15:15:36Z

On Tue, 18 Jan 2022 15:25:25 +0100
Jiri Olsa <jolsa@redhat.com> wrote:

> On Sat, Jan 15, 2022 at 01:52:19PM +0900, Masami Hiramatsu wrote:
> > On Thu, 13 Jan 2022 13:27:34 +0100
> > Jiri Olsa <jolsa@redhat.com> wrote:
> >
> > > On Wed, Jan 12, 2022 at 05:01:15PM +0100, Jiri Olsa wrote:
> > > > On Wed, Jan 12, 2022 at 11:02:46PM +0900, Masami Hiramatsu wrote:
> > > > > Hi Jiri and Alexei,
> > > > >
> > > > > Here is the 2nd version of fprobe. This version uses the
> > > > > ftrace_set_filter_ips() for reducing the registering overhead.
> > > > > Note that this also drops per-probe point private data, which
> > > > > is not used anyway.
> > > > >
> > > > > This introduces the fprobe, the function entry/exit probe with
> > > > > multiple probe point support. This also introduces the rethook
> > > > > for hooking function return as same as kretprobe does. This
> > > >
> > > > nice, I was going through the multi-user-graph support
> > > > and was wondering that this might be a better way
> > > >
> > > > > abstraction will help us to generalize the fgraph tracer,
> > > > > because we can just switch it from rethook in fprobe, depending
> > > > > on the kernel configuration.
> > > > >
> > > > > The patch [1/8] and [7/8] are from your series[1]. Other libbpf
> > > > > patches will not be affected by this change.
> > > >
> > > > I'll try the bpf selftests on top of this
> > >
> > > I'm getting crash and stall when running bpf selftests,
> > > the fprobe sample module works fine, I'll check on that
> >
> > OK, I got a kernel stall. I missed to enable CONFIG_FPROBE.
> > I think vmtest.sh should support menuconfig option.
> >
> > #6 bind_perm:OK
> > #7 bloom_filter_map:OK
> > [ 107.282403] clocksource: timekeeping watchdog on CPU0: Marking clocksource 'tsc' as unstable because the skew is too large:
> > [ 107.283240] clocksource: 'hpet' wd_nsec: 496216090 wd_now: 7ddc7120 wd_last: 7ae746b7 mask: ffffffff
> > [ 107.284045] clocksource: 'tsc' cs_nsec: 495996979 cs_now: 31fdb69b39 cs_last: 31c2d29219 mask: ffffffffffffffff
> > [ 107.284926] clocksource: 'tsc' is current clocksource.
> > [ 107.285487] tsc: Marking TSC unstable due to clocksource watchdog
> > [ 107.285973] TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'.
> > [ 107.286616] sched_clock: Marking unstable (107240582544, 45390230)<-(107291410145, -5437339)
> > [ 107.290408] clocksource: Not enough CPUs to check clocksource 'tsc'.
> > [ 107.290879] clocksource: Switched to clocksource hpet
> > [ 604.210415] INFO: rcu_tasks detected stalls on tasks:
> > [ 604.210830] (____ptrval____): .. nvcsw: 86/86 holdout: 1 idle_cpu: -1/0
> > [ 604.211314] task:test_progs state:R running task stack: 0 pid: 87 ppid: 85 flags:0x00004000
> > [ 604.212058] Call Trace:
> > [ 604.212246] <TASK>
> > [ 604.212452] __schedule+0x362/0xbb0
> > [ 604.212723] ? preempt_schedule_notrace_thunk+0x16/0x18
> > [ 604.213107] preempt_schedule_notrace+0x48/0x80
> > [ 604.217403] ? asm_sysvec_apic_timer_interrupt+0x12/0x20
> > [ 604.217790] ? ftrace_regs_call+0xd/0x52
> > [ 604.218087] ? bpf_test_finish.isra.0+0x190/0x190
> > [ 604.218461] ? bpf_fentry_test1+0x5/0x10
> > [ 604.218750] ? trace_clock_x86_tsc+0x10/0x10
> > [ 604.219064] ? __sys_bpf+0x8b1/0x2970
> > [ 604.219337] ? lock_is_held_type+0xd7/0x130
> > [ 604.219680] ? __x64_sys_bpf+0x1c/0x20
> > [ 604.219957] ? do_syscall_64+0x35/0x80
> > [ 604.220237] ? entry_SYSCALL_64_after_hwframe+0x44/0xae
> > [ 604.220653] </TASK>
> >
> > Jiri, is that what you had seen?
>
> hi,
> sorry for late response
>
> I did not get any backtrace for the stall, debugging showed
> that the first probed function was called over and over for
> some reason
>
> as for the crash I used the small fix below

Oops, good catch!

>
> do you have any newer version I could play with?

Let me update the fprobe and rethook. I'm now trying to integrate
the rethook with kretprobes and find some issues.

Thank you!

>
> jirka
>
>
> ---
> diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> index 3333893e5217..883151275892 100644
> --- a/kernel/trace/fprobe.c
> +++ b/kernel/trace/fprobe.c
> @@ -157,7 +157,8 @@ int unregister_fprobe(struct fprobe *fp)
> ret = unregister_ftrace_function(&fp->ftrace);
>
> if (!ret) {
> - rethook_free(fp->rethook);
> + if (fp->rethook)
> + rethook_free(fp->rethook);
> if (fp->syms) {
> kfree(fp->addrs);
> fp->addrs = NULL;
>

--
Masami Hiramatsu <mhiramat@kernel.org>