Re: [PATCH v2] tracing/uprobe: Add missing PID filter for uretprobe

Andrii Nakryiko
2024-08-26T22:08:45Z

On Mon, Aug 26, 2024 at 3:01 PM Jiri Olsa <olsajiri@gmail.com> wrote:
>
> On Mon, Aug 26, 2024 at 11:25:53PM +0200, Oleg Nesterov wrote:
> > This is offtopic, sorry for the spam, but...
> >
> > On 08/26, Jiri Olsa wrote:
> > >
> > > On Mon, Aug 26, 2024 at 01:57:52PM +0200, Oleg Nesterov wrote:
> > > >
> > > > Does bpftrace use bpf_uprobe_multi_link_attach/etc ? I guess not...
> > > > Then which userspace tool uses this code? ;)
> > >
> > > yes, it will trigger if you attach to multiple uprobes, like with your
> > > test example with:
> > >
> > > # bpftrace -p xxx -e 'uprobe:./ex:func* { printf("%d\n", pid); }'
> >
> > Hmm. I reserved the testing machine with fedora 40 to play with bpftrace.
> >
> > dummy.c:
> >
> > #include <unistd.h>
> >
> > void func1(void) {}
> > void func2(void) {}
> >
> > int main(void) { for (;;) pause(); }
> >
> > If I do
> >
> > # ./dummy &
> > # bpftrace -p $! -e 'uprobe:./dummy:func* { printf("%d\n", pid); }'
> >
> > and run
> >
> > # bpftrace -e 'kprobe:__uprobe_register { printf("%s\n", kstack); }'
>
> did you just bpftrace-ed bpftrace? ;-) on my setup I'm getting:
>
> [root@qemu ex]# ../bpftrace/build/src/bpftrace -e 'kprobe:uprobe_register { printf("%s\n", kstack); }'
> Attaching 1 probe...
>
> uprobe_register+1
> bpf_uprobe_multi_link_attach+685
> __sys_bpf+9395
> __x64_sys_bpf+26
> do_syscall_64+128
> entry_SYSCALL_64_after_hwframe+118
>
>
> I'm not sure what's bpftrace version in fedora 40, I'm using upstream build:
>
> [root@qemu ex]# ../bpftrace/build/src/bpftrace --info 2>&1 | grep uprobe_multi
> uprobe_multi: yes
> [root@qemu ex]# ../bpftrace/build/src/bpftrace --version
> bpftrace v0.20.0
>
>

So what's the conclusion for the original issue? Do we have a path
forward with the fix?

> jirka
>
> >
> > on another console I get
> >
> > Attaching 1 probe...
> >
> > __uprobe_register+1
> > probe_event_enable+399
> > perf_trace_event_init+440
> > perf_uprobe_init+152
> > perf_uprobe_event_init+74
> > perf_try_init_event+71
> > perf_event_alloc+1681
> > __do_sys_perf_event_open+447
> > do_syscall_64+130
> > entry_SYSCALL_64_after_hwframe+118
> >
> > __uprobe_register+1
> > probe_event_enable+399
> > perf_trace_event_init+440
> > perf_uprobe_init+152
> > perf_uprobe_event_init+74
> > perf_try_init_event+71
> > perf_event_alloc+1681
> > __do_sys_perf_event_open+447
> > do_syscall_64+130
> > entry_SYSCALL_64_after_hwframe+118
> >
> > so it seems that bpftrace doesn't use bpf_uprobe_multi_link_attach()
> > (called by sys_bpf(BPF_LINK_CREATE) ?) in this case.
> >
> > But again, this is offtopic, please forget.
> >
> > Oleg.
> >