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From:   Ze Gao <zegao2021@gmail.com>
Date:   Tue, 16 May 2023 17:51:34 +0800
Message-ID: <CAD8CoPDu=u4vxEYiaZfne92yZ=uTcAEPzWPbdjncyfbSyuCpfg@mail.gmail.com>
Subject: Re: [PATCH v2 2/4] fprobe: make fprobe_kprobe_handler recursion free
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <mhiramat@kernel.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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Sorry for paste the wrong link, it's this one instead:
  Link: https://lore.kernel.org/bpf/20230513001757.75ae0d1b@rorschach.local=
.home/

It's the original discussions of this problem.

Regards,
Ze

On Tue, May 16, 2023 at 5:47=E2=80=AFPM Ze Gao <zegao2021@gmail.com> wrote:
>
> Precisely, these that are called within kprobe_busy_{begin, end},
> which the previous patch does not resolve.
> 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.c902e=
dcf21028874a74fb868@kernel.org/
>
> Regards,
> Ze
>
> On Tue, May 16, 2023 at 5:18=E2=80=AFPM Peter Zijlstra <peterz@infradead.=
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?