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

[Menglong Dong <menglong.dong@linux.dev>]

On 2025/12/18 22:45 Andreas Schwab <schwab@linux-m68k.org> write:
> 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@chinatelecom.cn>
> > Acked-by: Alexei Starovoitov <ast@kernel.org>
> 
> This breaks RISC-V:

Hi, Andreas. Can you offer more information here? After my analysis,
I didn't see the problem. BPF_TRAMP_F_SKIP_FRAME and
BPF_TRAMP_F_ORIG_STACK are set together all the time in RISC-V, so
I changed BPF_TRAMP_F_SKIP_FRAME to BPF_TRAMP_F_ORIG_STACK
*should* have no influence.

Thanks!
Menglong Dong

> 
> [    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@linux-m68k.org
> GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
> "And now for something completely different."
> 
>