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From: "Daniel Xu" <dxu@dxuuu.xyz>
To: mhiramat@kernel.org
Cc: linux-kernel@vger.kernel.org,
	"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
	kuba@kernel.org
Subject: Broken kretprobe stack traces
Date: Tue, 02 Mar 2021 17:15:13 -0800	[thread overview]
Message-ID: <1fed0793-391c-4c68-8d19-6dcd9017271d@www.fastmail.com> (raw)

Hi Masami,

Jakub reported a bug with kretprobe stack traces -- wondering if you've gotten
any bug reports related to stack traces being broken for kretprobes.

I think (can't prove) this used to work:

    # bpftrace -e 'kretprobe:__tcp_retransmit_skb { @[kstack()] = count() }'
    Attaching 1 probe...
    ^C

    @[
        kretprobe_trampoline+0
    ]: 1

fentry/fexit probes seem to work:

    # bpftrace -e 'kretfunc:__tcp_retransmit_skb { @[kstack()] = count() }'
    Attaching 1 probe...
    ^C
    
    @[
        ftrace_trampoline+10799
        bpf_get_stackid_raw_tp+121
        ftrace_trampoline+10799
        __tun_chr_ioctl.isra.0.cold+33312
        __tcp_retransmit_skb+5
        tcp_send_loss_probe+254
        tcp_write_timer_handler+394
        tcp_write_timer+149
        call_timer_fn+41
        __run_timers+493
        run_timer_softirq+25
        __softirqentry_text_start+207
        asm_call_sysvec_on_stack+18
        do_softirq_own_stack+55
        irq_exit_rcu+158
        sysvec_apic_timer_interrupt+54
        asm_sysvec_apic_timer_interrupt+18
    ]: 1
    @[
        ftrace_trampoline+10799
        bpf_get_stackid_raw_tp+121
        ftrace_trampoline+10799
        __tun_chr_ioctl.isra.0.cold+33312
        __tcp_retransmit_skb+5
  <...>

which makes me suspect it's a kprobe specific issue.

Thanks,
Daniel

             reply	other threads:[~2021-03-03  3:56 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-03  1:15 Daniel Xu [this message]
2021-03-03  4:48 ` Broken kretprobe stack traces Masami Hiramatsu
2021-03-03 14:26   ` Steven Rostedt
2021-03-03 19:58     ` Daniel Xu
2021-03-03 20:13       ` Daniel Xu
2021-03-03 20:37         ` Steven Rostedt
2021-03-04  2:18           ` Daniel Xu
2021-03-04 19:04             ` Daniel Xu
2021-03-04 13:19     ` Masami Hiramatsu
2021-03-04 15:22       ` [PATCH] kprobes: stacktrace: Recover the address changed by kretprobe kernel test robot
2021-03-04 17:37       ` kernel test robot
2021-03-04 20:25       ` kernel test robot
2021-03-03 19:57   ` Broken kretprobe stack traces Daniel Xu

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