linux-kernel - Re: [PATCH] arch/x86: get rid of KERN_CONT in show_fault

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Date:   Thu, 21 Jun 2018 09:59:05 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Dmitry Vyukov <dvyukov@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH] arch/x86: get rid of KERN_CONT in show_fault_oops()

On Thu, Jun 21, 2018 at 3:06 AM, Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> On Wed, Jun 20, 2018 at 3:55 PM, Dmitry Vyukov <dvyukov@...il.com> wrote:
>> From: Dmitry Vyukov <dvyukov@...gle.com>
>>
>> KERN_CONT leads to split lines in kernel output
>> and complicates useful changes to printk like
>> printing context before each line.
>>
>> Only acceptable use of continuations is basically
>> boot-time testing.
>>
>> Get rid of it.
>
>> +       printk(KERN_ALERT "BUG: unable to handle kernel %s at %px\n",
>> +               (address < PAGE_SIZE ? "NULL pointer dereference" :
>> +               "paging request"), (void *) address);
>
> Perhaps pr_alert() ?

It's the same, right? Make sense.

> Btw, parens are redundant for the first argument.
>
> P.S. And personally I would rather do
> if (address < PAGE_SIZE)
>  pr_alert(...NULL pointer dereference...);
> else
>  pr_alert(...paging request...);

It's kinda shorter this way. Any other opinions?

pr_alert("BUG: unable to handle kernel %s at %px\n",
        address < PAGE_SIZE ? "NULL pointer dereference" :
        "paging request", (void *) address);

vs:

if (address < PAGE_SIZE)
        pr_alert("BUG: unable to handle kernel NULL pointer
dereference at %px\n",
                (void *) address);
else
        pr_alert("BUG: unable to handle kernel paging request at %px\n",
                (void *) address);

Or, should we just do:

pr_alert("BUG: unable to handle kernel paging request at %px\n",
        (void *) address);

and not try to be too smart here? In the end, that can be a NULL deref
with 5K offset, right?