linux-kernel - Re: [PATCH v2 bpf-next 2/4] bpf: introduce helper bpf_get_task

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Message-ID: <CAEf4BzZ-a1gB8wjf85n=EbRUETOgrhXHa_+vAXoEeFun5GTr=g@mail.gmail.com>
Date:   Fri, 26 Jun 2020 13:22:03 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Peter Ziljstra <peterz@...radead.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCH v2 bpf-next 2/4] bpf: introduce helper bpf_get_task_stak()

On Fri, Jun 26, 2020 at 1:17 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Thu, Jun 25, 2020 at 5:14 PM Song Liu <songliubraving@...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.
> >
> > Signed-off-by: Song Liu <songliubraving@...com>
> > ---
>
> Looks great, I just think that there are cases where user doesn't
> necessarily has valid task_struct pointer, just pid, so would be nice
> to not artificially restrict such cases by having extra helper.
>
> Acked-by: Andrii Nakryiko <andriin@...com>

oh, please also fix a typo in the subject, it will make grepping more
frustrating

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