linux-kernel - Re: [PATCH] x86/mm/ptdump: Fix soft lockup in page table walker.

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Date:   Fri, 10 Feb 2017 12:18:22 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dmitry Vyukov <dvyukov@...gle.com>
cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        Tobias Regnery <tobias.regnery@...il.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH] x86/mm/ptdump: Fix soft lockup in page table walker.

On Fri, 10 Feb 2017, Dmitry Vyukov wrote:
> This is the right thing to do per se, but I am concerned that now
> people will just suffers from slow boot (it can take literally
> minutes) and will not realize the root cause nor that it's fixable
> (e.g. with rodata=n) and will probably just blame KASAN for slowness.
> 
> Could we default this rodata check to n under KASAN? Or at least print
> some explanatory warning message before doing marking rodata (it
> should be printed right before "hang", so if you stare at it for a
> minute during each boot you realize that it may be related)? Or
> something along these lines. FWIW in my builds I just always disable
> the check.

That certainly makes sense and we emit such warnings in other places
already (lockdep, trace_printk ...)

Thanks,

	tglx