linux-kernel - Re: [PATCH bpf-next v3 3/6] bpf: fix the usage of BPF_TRAMP_F_SKIP

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Message-ID: <874ipnkfvt.fsf@igel.home>
Date: Thu, 18 Dec 2025 15:45:42 +0100
From: Andreas Schwab <schwab@...ux-m68k.org>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: ast@...nel.org,  rostedt@...dmis.org,  daniel@...earbox.net,
  john.fastabend@...il.com,  andrii@...nel.org,  martin.lau@...ux.dev,
  eddyz87@...il.com,  song@...nel.org,  yonghong.song@...ux.dev,
  kpsingh@...nel.org,  sdf@...ichev.me,  haoluo@...gle.com,
  jolsa@...nel.org,  mhiramat@...nel.org,  mark.rutland@....com,
  mathieu.desnoyers@...icios.com,  jiang.biao@...ux.dev,
  bpf@...r.kernel.org,  linux-kernel@...r.kernel.org,
  linux-trace-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH bpf-next v3 3/6] bpf: fix the usage of
 BPF_TRAMP_F_SKIP_FRAME

On Nov 18 2025, Menglong Dong wrote:

> Some places calculate the origin_call by checking if
> BPF_TRAMP_F_SKIP_FRAME is set. However, it should use
> BPF_TRAMP_F_ORIG_STACK for this propose. Just fix them.
>
> Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
> Acked-by: Alexei Starovoitov <ast@...nel.org>

This breaks RISC-V:

[    8.584381][    T1] systemd[1]: bpf-restrict-fs: LSM BPF program attached
[    8.588359][    T1] Insufficient stack space to handle exception!
[    8.588823][    T1] Task stack:     [0xff20000000010000..0xff20000000014000]
[    8.589219][    T1] Overflow stack: [0xff600000ffdad070..0xff600000ffdae070]
[    8.590133][    T1] CPU: 1 UID: 0 PID: 1 Comm: systemd Not tainted 6.18.0-rc5+ #15 PREEMPT(voluntary)  c900881ed1c1988ec5cf3e914d0edeb1b4d83ca3
[    8.590898][    T1] Hardware name: riscv-virtio qemu/qemu, BIOS 2025.10 10/01/2025
[    8.591494][    T1] epc : copy_from_kernel_nofault+0xa/0x198
[    8.592292][    T1]  ra : bpf_probe_read_kernel+0x20/0x60
[    8.592658][    T1] epc : ffffffff802b732a ra : ffffffff801e6070 sp : ff2000000000ffe0
[    8.593121][    T1]  gp : ffffffff82262ed0 tp : 0000000000000000 t0 : ffffffff80022320
[    8.593566][    T1]  t1 : ffffffff801e6056 t2 : 0000000000000000 s0 : ff20000000010040
[    8.593997][    T1]  s1 : 0000000000000008 a0 : ff20000000010050 a1 : ff60000083b3d320
[    8.594446][    T1]  a2 : 0000000000000008 a3 : 0000000000000097 a4 : 0000000000000000
[    8.594940][    T1]  a5 : 0000000000000000 a6 : 0000000000000021 a7 : 0000000000000003
[    8.595396][    T1]  s2 : ff20000000010050 s3 : ff6000008459fc18 s4 : ff60000083b3d340
[    8.595831][    T1]  s5 : ff20000000010060 s6 : 0000000000000000 s7 : ff20000000013aa8
[    8.596215][    T1]  s8 : 0000000000000000 s9 : 0000000000008000 s10: 000000000058dcb0
[    8.596641][    T1]  s11: 000000000058dca7 t3 : 000000006925116d t4 : ff6000008090f026
[    8.597065][    T1]  t5 : 00007fff9b0cbaa8 t6 : 0000000000000016
[    8.597363][    T1] status: 0000000200000120 badaddr: 0000000000000000 cause: 8000000000000005
[    8.598033][    T1] Kernel panic - not syncing: Kernel stack overflow
[    8.598597][    T1] CPU: 1 UID: 0 PID: 1 Comm: systemd Not tainted 6.18.0-rc5+ #15 PREEMPT(voluntary)  c900881ed1c1988ec5cf3e914d0edeb1b4d83ca3
[    8.599244][    T1] Hardware name: riscv-virtio qemu/qemu, BIOS 2025.10 10/01/2025
[    8.599659][    T1] Call Trace:
[    8.600117][    T1] [<ffffffff8001a1f8>] dump_backtrace+0x28/0x38
[    8.600517][    T1] [<ffffffff80002502>] show_stack+0x3a/0x50
[    8.600844][    T1] [<ffffffff800122be>] dump_stack_lvl+0x56/0x80
[    8.601176][    T1] [<ffffffff80012300>] dump_stack+0x18/0x22
[    8.601518][    T1] [<ffffffff80002abe>] vpanic+0xf6/0x328
[    8.601819][    T1] [<ffffffff80002d2e>] panic+0x3e/0x40
[    8.602088][    T1] [<ffffffff80019ef0>] handle_bad_stack+0x98/0xa0
[    8.602395][    T1] [<ffffffff801e6070>] bpf_probe_read_kernel+0x20/0x60

-- 
Andreas Schwab, schwab@...ux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."