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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Mon, 29 Jun 2020 21:18:33 -0700
Message-ID: <CAADnVQJUdLKmdMu_eAX3ZGjf5K8GMkow+KoBSTTqy6CftgmdTw@mail.gmail.com>
Subject: Re: [PATCH v4 bpf-next 2/4] bpf: introduce helper bpf_get_task_stack()
To:     Song Liu <songliubraving@fb.com>
Cc:     bpf <bpf@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Kernel Team <kernel-team@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@chromium.org>,
        Andrii Nakryiko <andriin@fb.com>
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On Sun, Jun 28, 2020 at 10:58 PM Song Liu <songliubraving@fb.com> 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@fb.com>
> Signed-off-by: Song Liu <songliubraving@fb.com>

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()