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

Jiri Olsa
2022-02-02T00:02:52Z

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?

thanks,
jirka