linux-kernel - Re: [next] i386: kunit: ASSERTION FAILED at mm/kfence/kfence

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Message-ID: <87czgwmgtc.fsf@jogness.linutronix.de>
Date:   Mon, 02 May 2022 11:26:31 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>, Marco Elver <elver@...gle.com>
Cc:     Naresh Kamboju <naresh.kamboju@...aro.org>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        lkft-triage@...ts.linaro.org, linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Anders Roxell <anders.roxell@...aro.org>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Peter Collingbourne <pcc@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will@...nel.org>
Subject: Re: [next] i386: kunit: ASSERTION FAILED at
 mm/kfence/kfence_test.c:547

On 2022-05-02, Petr Mladek <pmladek@...e.com> wrote:
>> My proposal would be to fix the tracepoint like so:
>> 
>>  | --- a/kernel/printk/printk.c
>>  | +++ b/kernel/printk/printk.c
>>  | @@ -2002,8 +2002,6 @@ static void call_console_driver(struct console *con, const char *text, size_t le
>>  |  {
>>  |  	size_t dropped_len;
>>  |  
>>  | -	trace_console_rcuidle(text, len);
>>  | -
>>  |  	if (con->dropped && dropped_text) {
>>  |  		dropped_len = snprintf(dropped_text, DROPPED_TEXT_MAX,
>>  |  				       "** %lu printk messages dropped **\n",
>>  | @@ -2178,6 +2176,8 @@ static u16 printk_sprint(char *text, u16 size, int facility,
>>  |  		}
>>  |  	}
>>  |  
>>  | +	trace_console_rcuidle(text, text_len);
>>  | +
>>  |  	return text_len;
>>  |  }
>> 
>> This fixes the KFENCE and KCSAN tests.
>> 
>> Unless I hear objections, I'll prepare a patch explaining why we need to
>> fix the tracepoint.
>
> It makes perfect sense to me.

This is the easiest place for it. However, it should be clear that in
the context of trace_console_rcuidle(), the message is not yet visible
to any readers. The message _will_ get committed and definitely _will_
become visible at some point. But it is not (yet) visible at _this_
point. Maybe that is OK for what it is being used for.

If trace_console_rcuidle() must be called at the point of visibility for
readers, it becomes more complicated.

John