netdev - Re: [PATCH] perf: fix panic by disable ftrace on fault.c

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Date:   Wed, 15 Sep 2021 15:34:20 +0800
From:   王贇 <yun.wang@...ux.alibaba.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        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>,
        "open list:X86 MM" <linux-kernel@...r.kernel.org>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <netdev@...r.kernel.org>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <bpf@...r.kernel.org>
Subject: Re: [PATCH] perf: fix panic by disable ftrace on fault.c



On 2021/9/15 下午3:22, 王贇 wrote:
> 
> 
> On 2021/9/15 上午11:27, Dave Hansen wrote:
>> On 9/14/21 6:56 PM, 王贇 wrote:
>>>>> [   44.134987][    C0]  ? __sanitizer_cov_trace_pc+0x7/0x60
>>>>> [   44.135005][    C0]  ? kcov_common_handle+0x30/0x30
>>>> Just turning off tracing for the page fault handler is papering over the
>>>> problem.  It'll just come back later with a slightly different form.
>>>>
>>> Cool~ please let me know when you have the proper approach.
>>
>> It's an entertaining issue, but I wasn't planning on fixing it myself.
>>
> 
> Do you have any suggestion on how should we fix the problem?
> 
> I'd like to help fix it, but sounds like all the known working approach
> are not acceptable...

Hi, Dave, Peter

What if we just increase the stack size when ftrace enabled?

Maybe like:

diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
index a8d4ad85..bc2e0c1 100644
--- a/arch/x86/include/asm/page_64_types.h
+++ b/arch/x86/include/asm/page_64_types.h
@@ -12,10 +12,16 @@
 #define KASAN_STACK_ORDER 0
 #endif

+#ifdef CONFIG_FUNCTION_TRACER
+#define FTRACE_STACK_ORDER 1
+#else
+#define FTRACE_STACK_ORDER 0
+#endif
+
 #define THREAD_SIZE_ORDER      (2 + KASAN_STACK_ORDER)
 #define THREAD_SIZE  (PAGE_SIZE << THREAD_SIZE_ORDER)

-#define EXCEPTION_STACK_ORDER (0 + KASAN_STACK_ORDER)
+#define EXCEPTION_STACK_ORDER (0 + KASAN_STACK_ORDER + FTRACE_STACK_ORDER)
 #define EXCEPTION_STKSZ (PAGE_SIZE << EXCEPTION_STACK_ORDER)

 #define IRQ_STACK_ORDER (2 + KASAN_STACK_ORDER)

Just like kasan we give more stack space for ftrace, is this looks
acceptable to you?

Regards,
Michael Wang

> 
> Regards,
> Michael Wang
>