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

[Jiri Olsa <olsajiri@gmail.com>]

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


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.
>