Re: [PATCH v4 bpf-next 2/4] bpf: introduce helper bpf_get_task_stack()

[Alexei Starovoitov]

On Sun, Jun 28, 2020 at 10:58 PM Song Liu <songliubraving@xxxxxx> wrote:
>
> Introduce helper bpf_get_task_stack(), which dumps stack trace of given
> task. This is different to bpf_get_stack(), which gets stack track of
> current task. One potential use case of bpf_get_task_stack() is to call
> it from bpf_iter__task and dump all /proc/<pid>/stack to a seq_file.
>
> bpf_get_task_stack() uses stack_trace_save_tsk() instead of
> get_perf_callchain() for kernel stack. The benefit of this choice is that
> stack_trace_save_tsk() doesn't require changes in arch/. The downside of
> using stack_trace_save_tsk() is that stack_trace_save_tsk() dumps the
> stack trace to unsigned long array. For 32-bit systems, we need to
> translate it to u64 array.
>
> Acked-by: Andrii Nakryiko <andriin@xxxxxx>
> Signed-off-by: Song Liu <songliubraving@xxxxxx>

It doesn't apply:
Applying: bpf: Introduce helper bpf_get_task_stack()
Using index info to reconstruct a base tree...
error: patch failed: kernel/bpf/stackmap.c:471
error: kernel/bpf/stackmap.c: patch does not apply
error: Did you hand edit your patch?
It does not apply to blobs recorded in its index.
Patch failed at 0002 bpf: Introduce helper bpf_get_task_stack()