linux-kernel - Re: radeon.ko/i586: BUG: kernel NULL pointer dereference,address:00000004

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Message-ID: <230721083955.M0102626@vega.pgw.jp>
Date:   Fri, 21 Jul 2023 08:39:55 +0900
From:   <kkabe@...a.pgw.jp>
To:     rostedt@...dmis.org
Cc:     regressions@...ts.linux.dev, bagasdotme@...il.com,
        alexander.deucher@....com, christian.koenig@....com,
        Xinhui.Pan@....com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        kkabe@...a.pgw.jp
Subject: Re: radeon.ko/i586: BUG: kernel NULL pointer dereference,address:00000004

rostedt@...dmis.org sed in <20230717113623.41878887@...dalf.local.home>

>> On Fri, 14 Jul 2023 14:34:04 +0900
>> <kkabe@...a.pgw.jp> wrote:
>> 
>> > Patch in
>> > https://bugzilla.kernel.org/show_bug.cgi?id=217669#c4
>> > fixed the problem in freedesktop.org kernel 5.18.0-rc2 .
>> > This may explain that in kernel.org tree, the said commit is in kernel-5.19.
>> 
>> You mean the patch that adds:
>> 
>> 	#if defined(FTRACE_MCOUNT_MAX_OFFSET) && (FTRACE_MCOUNT_MAX_OFFSET)
>> 
>> ?
>> 
>> Nothing should be setting FTRACE_MCOUNT_MAX_OFFSET to anything but non
>> zero. But doing a grep, I now see:
>> 
>> # define FTRACE_MCOUNT_MAX_OFFSET ENDBR_INSN_SIZE
>> 
>> Where it breaks that assumption if ENDBR_INSN_SIZE == 0 :-p
>>  (and that's my code!)
>> 
>> OK, does this fix it? (I haven't tested nor compiled this)
>> 
>> -- Steve
>> 
>> diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
>> index 897cf02c20b1..801f4414da3e 100644
>> --- a/arch/x86/include/asm/ftrace.h
>> +++ b/arch/x86/include/asm/ftrace.h
>> @@ -13,7 +13,7 @@
>>  #ifdef CONFIG_HAVE_FENTRY
>>  # include <asm/ibt.h>
>>  /* Add offset for endbr64 if IBT enabled */
>> -# define FTRACE_MCOUNT_MAX_OFFSET	ENDBR_INSN_SIZE
>> +# define FTRACE_MCOUNT_MAX_OFFSET	(ENDBR_INSN_SIZE + MCOUNT_INSN_SIZE)
>>  #endif
>>  
>>  #ifdef CONFIG_DYNAMIC_FTRACE
>> 

Unfortunately this patch didn't fix freedesktop.org 5.18.0-rc2 tree.
(vblank->worker == NULL check fires otherwise a panic)

Applying this to kernel.org 6.4.3 results in totally different error as in 
https://bugzilla.kernel.org/show_bug.cgi?id=217669#c0
so there may be multiple regressions I'm chasing.

-- 
kabe