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From:   Ze Gao <zegao2021@gmail.com>
Date:   Wed, 17 May 2023 09:54:53 +0800
Message-ID: <CAD8CoPAw_nKsm4vUJ_=aSwzLc5zo8D5pY6A7-grXENxpMYz9og@mail.gmail.com>
Subject: Re: [PATCH v2 2/4] fprobe: make fprobe_kprobe_handler recursion free
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vasily Gorbik <gor@linux.ibm.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
        linux-s390@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
        bpf@vger.kernel.org, Conor Dooley <conor@kernel.org>,
        Jiri Olsa <jolsa@kernel.org>, Yonghong Song <yhs@fb.com>,
        Ze Gao <zegao@tencent.com>
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Oops, I misunderstood your comments before.

Yes, it's not necessary to do this reordering as regards to kprobe.

Thanks for your review.

I'll rebase onto the latest tree and send v3 ASAP.

Regards,
Ze

On Wed, May 17, 2023 at 12:03=E2=80=AFAM Masami Hiramatsu <mhiramat@kernel.=
org> wrote:
>
> On Tue, 16 May 2023 17:47:52 +0800
> Ze Gao <zegao2021@gmail.com> wrote:
>
> > Precisely, these that are called within kprobe_busy_{begin, end},
> > which the previous patch does not resolve.
>
> Note that kprobe_busy_{begin,end} don't need to use notrace version
> because kprobe itself prohibits probing on preempt_count_{add,sub}.
>
> Thank you,
>
> > I will refine the commit message to make it clear.
> >
> > FYI, details can checked out here:
> >     Link: https://lore.kernel.org/linux-trace-kernel/20230516132516.c90=
2edcf21028874a74fb868@kernel.org/
> >
> > Regards,
> > Ze
> >
> > On Tue, May 16, 2023 at 5:18=E2=80=AFPM Peter Zijlstra <peterz@infradea=
d.org> wrote:
> > >
> > > On Tue, May 16, 2023 at 03:18:28PM +0800, Ze Gao wrote:
> > > > Current implementation calls kprobe related functions before doing
> > > > ftrace recursion check in fprobe_kprobe_handler, which opens door
> > > > to kernel crash due to stack recursion if preempt_count_{add, sub}
> > > > is traceable.
> > >
> > > Which preempt_count*() are you referring to? The ones you just made
> > > _notrace in the previous patch?
>
>
> --
> Masami Hiramatsu (Google) <mhiramat@kernel.org>