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

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Date:   Tue, 26 Apr 2022 15:36:02 +0800
From:   Xu Kuohai <xukuohai@...wei.com>
To:     Steven Rostedt <rostedt@...dmis.org>
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 4/25/2022 11:05 PM, Steven Rostedt wrote:
> 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
> 
> 

will move this to arch/arm64/ in v4, thanks.

> 
> 
>> +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
> 
> .