linux-kernel - Re: [PATCH bpf-next v3 2/7] ftrace: Fix deadloop caused by direct call in ftrace selftest

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Message-ID: <20220425110512.538ce0bf@gandalf.local.home>
Date:   Mon, 25 Apr 2022 11:05:12 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Xu Kuohai <xukuohai@...wei.com>
Cc:     <bpf@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Zi Shen Lim <zlim.lnx@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        <hpa@...or.com>, Shuah Khan <shuah@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Daniel Kiss <daniel.kiss@....com>,
        Steven Price <steven.price@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Marc Zyngier <maz@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Mark Brown <broonie@...nel.org>,
        Delyan Kratunov <delyank@...com>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>
Subject: Re: [PATCH bpf-next v3 2/7] ftrace: Fix deadloop caused by direct
 call in ftrace selftest

On Sun, 24 Apr 2022 11:40:23 -0400
Xu Kuohai <xukuohai@...wei.com> wrote:

> diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
> index abcadbe933bb..d2eff2b1d743 100644
> --- a/kernel/trace/trace_selftest.c
> +++ b/kernel/trace/trace_selftest.c
> @@ -785,8 +785,24 @@ static struct fgraph_ops fgraph_ops __initdata  = {
>  };
>  
>  #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
> +#ifdef CONFIG_ARM64

Please find a way to add this in arm specific code. Do not add architecture
defines in generic code.

You could add:

#ifndef ARCH_HAVE_FTRACE_DIRECT_TEST_FUNC
noinline __noclone static void trace_direct_tramp(void) { }
#endif

here, and in arch/arm64/include/ftrace.h

#define ARCH_HAVE_FTRACE_DIRECT_TEST_FUNC

and define your test function in the arm64 specific code.

-- Steve




> +extern void trace_direct_tramp(void);
> +
> +asm (
> +"	.pushsection	.text, \"ax\", @progbits\n"
> +"	.type		trace_direct_tramp, %function\n"
> +"	.global		trace_direct_tramp\n"
> +"trace_direct_tramp:"
> +"	mov	x10, x30\n"
> +"	mov	x30, x9\n"
> +"	ret	x10\n"
> +"	.size		trace_direct_tramp, .-trace_direct_tramp\n"
> +"	.popsection\n"
> +);
> +#else
>  noinline __noclone static void trace_direct_tramp(void) { }
>  #endif
> +#endif
>  
>  /*
>   * Pretty much the same than for the function tracer from which the selftest