Re: [PATCH v7 00/10] fprobe: Introduce fprobe function entry/exit probe

Andrii Nakryiko
2022-02-02T00:09:20Z

On Tue, Feb 1, 2022 at 4:02 PM Jiri Olsa <jolsa@redhat.com> wrote:
>
> On Mon, Jan 31, 2022 at 02:00:24PM +0900, Masami Hiramatsu wrote:
> > Hi,
> >
> > Here is the 7th version of fprobe. This version fixes unregister_fprobe()
> > ensures that exit_handler is not called after returning from the
> > unregister_fprobe(), and fixes some comments and documents.
> >
> > The previous version is here[1];
> >
> > [1] https://lore.kernel.org/all/164338031590.2429999.6203979005944292576.stgit@devnote2/T/#u
> >
> > This series 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 the kretprobe does. This
> > abstraction will help us to generalize the fgraph tracer,
> > because we can just switch to it from the rethook in fprobe,
> > depending on the kernel configuration.
> >
> > The patch [1/10] is from Jiri's series[2].
> >
> > [2] https://lore.kernel.org/all/20220104080943.113249-1-jolsa@kernel.org/T/#u
> >
> > And the patch [9/10] adds the FPROBE_FL_KPROBE_SHARED flag for the case
> > if user wants to share the same code (or share a same resource) on the
> > fprobe and the kprobes.
>
> hi,
> it works fine for bpf selftests, but when I use it through bpftrace
> to attach more probes with:
>
> # ./src/bpftrace -e 'kprobe:ksys_* { }'
> Attaching 27 probes
>
> I'm getting stalls like:
>
> krava33 login: [ 988.574069] INFO: task bpftrace:4137 blocked for more than 122 seconds.
> [ 988.577577] Not tainted 5.16.0+ #89
> [ 988.580173] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [ 988.585538] task:bpftrace state:D stack: 0 pid: 4137 ppid: 4123 flags:0x00004004
> [ 988.589869] Call Trace:
> [ 988.591312] <TASK>
> [ 988.592577] __schedule+0x3a8/0xd30
> [ 988.594469] ? wait_for_completion+0x84/0x110
> [ 988.596753] schedule+0x4e/0xc0
> [ 988.598480] schedule_timeout+0xed/0x130
> [ 988.600524] ? rcu_read_lock_sched_held+0x12/0x70
> [ 988.602901] ? lock_release+0x253/0x4a0
> [ 988.604935] ? lock_acquired+0x1b7/0x410
> [ 988.607041] ? trace_hardirqs_on+0x1b/0xe0
> [ 988.609202] wait_for_completion+0xae/0x110
> [ 988.613762] __wait_rcu_gp+0x127/0x130
> [ 988.615787] synchronize_rcu_tasks_generic+0x46/0xa0
> [ 988.618329] ? call_rcu_tasks+0x20/0x20
> [ 988.620600] ? rcu_tasks_pregp_step+0x10/0x10
> [ 988.623232] ftrace_shutdown.part.0+0x174/0x210
> [ 988.625820] unregister_ftrace_function+0x37/0x60
> [ 988.628480] unregister_fprobe+0x2d/0x50
> [ 988.630928] bpf_link_free+0x4e/0x70
> [ 988.633126] bpf_link_release+0x11/0x20
> [ 988.635249] __fput+0xae/0x270
> [ 988.637022] task_work_run+0x5c/0xa0
> [ 988.639016] exit_to_user_mode_prepare+0x251/0x260
> [ 988.641294] syscall_exit_to_user_mode+0x16/0x50
> [ 988.646249] do_syscall_64+0x48/0x90
> [ 988.648218] entry_SYSCALL_64_after_hwframe+0x44/0xae
> [ 988.650787] RIP: 0033:0x7f9079e95fbb
> [ 988.652761] RSP: 002b:00007ffd474fa3b0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
> [ 988.656718] RAX: 0000000000000000 RBX: 00000000011bf8d0 RCX: 00007f9079e95fbb
> [ 988.660110] RDX: 0000000000000000 RSI: 00007ffd474fa3b0 RDI: 0000000000000019
> [ 988.663512] RBP: 00007ffd474faaf0 R08: 0000000000000000 R09: 000000000000001a
> [ 988.666673] R10: 0000000000000064 R11: 0000000000000293 R12: 0000000000000001
> [ 988.669770] R13: 00000000004a19a1 R14: 00007f9083428c00 R15: 00000000008c02d8
> [ 988.672601] </TASK>
> [ 988.675763] INFO: lockdep is turned off.
>
> I have't investigated yet, any idea?
>

Do you happen to have a CPU count that's not a power of 2? Check if
you have [0] in your tree, it might be that.

[0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a773abf72eb0cac008743891068ca6edecc44683

> thanks,
> jirka
>