linux-kernel - Re: [PATCH v5 4/4] printk: use the lockless ringbuffer

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Message-ID: <87eep6sd1e.fsf@jogness.linutronix.de>
Date:   Mon, 20 Jul 2020 12:26:45 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Marco Elver <elver@...gle.com>
Cc:     Petr Mladek <pmladek@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrea Parri <parri.andrea@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul McKenney <paulmck@...nel.org>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/4] printk: use the lockless ringbuffer

On 2020-07-18, Marco Elver <elver@...gle.com> wrote:
> It seems this causes a regression observed at least with newline-only
> printks.
> [...]
> ------ >8 ------
>
> --- a/init/main.c
> +++ b/init/main.c
> @@ -1039,6 +1039,10 @@ asmlinkage __visible void __init start_kernel(void)
>  	sfi_init_late();
>  	kcsan_init();
>  
> +	pr_info("EXPECT BLANK LINE --vv\n");
> +	pr_info("\n");
> +	pr_info("EXPECT BLANK LINE --^^\n");
> +
>  	/* Do the rest non-__init'ed, we're now alive */
>  	arch_call_rest_init();

Thanks for the example. This is an unintentional regression in the
series. I will submit a patch to fix this.

Note that this regression does not exist when the followup series [0]
(reimplementing LOG_CONT) is applied. All the more reason that the 1st
series should be fixed before pushing the 2nd series to linux-next.

John Ogness

[0] https://lkml.kernel.org/r/20200717234818.8622-1-john.ogness@linutronix.de