linux-kernel - Re: [lkp-robot] [x86/cpu_entry_area] 10043e02db: kernel_BUG_at

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Date:   Thu, 28 Dec 2017 12:51:14 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dmitry Vyukov <dvyukov@...gle.com>
cc:     kernel test robot <xiaolong.ye@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>,
        LKML <linux-kernel@...r.kernel.org>, tipbuild@...or.com,
        LKP <lkp@...org>, Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [lkp-robot] [x86/cpu_entry_area] 10043e02db:
 kernel_BUG_at_arch/x86/mm/physaddr.c

On Wed, 27 Dec 2017, Dmitry Vyukov wrote:
> On Wed, Dec 27, 2017 at 7:05 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > So this dies simply because kasan_populate_shadow() runs out of memory and
> > has no sanity check whatsoever.
> >
> > static __init void *early_alloc(size_t size, int nid)
> > {
> >         return memblock_virt_alloc_try_nid_nopanic(size, size,
> >                 __pa(MAX_DMA_ADDRESS), BOOTMEM_ALLOC_ACCESSIBLE, nid);
> > }
> >
> > kasan_populate_pmd()
> > {
> >         .....
> >
> >                 p = early_alloc(PAGE_SIZE, nid);
> >                 entry = pfn_pte(PFN_DOWN(__pa(p)), PAGE_KERNEL);
> >
> > I've instrumented the whole thing and early_alloc() returns NULL at some
> > point and then __pa(NULL) dies in the VIRTUAL_DEBUG code. Well, it would
> > die with VIRTUAL_DEBUG=n as well at some other place.
> >
> > Not really a problem caused by the patch above, it's merily exposing a code
> > path which relies blindly on "enough memory available" assumptions.
> >
> > Throwing more memory at the VM makes the problem go away...
> 
> Hi Thomas,
> 
> We just need a check inside of early_alloc() to properly diagnose such
> situation, right?

At least you want to panic with a proper out of memory message. But letting
the thing die at a random place is a bad idea.

Thanks,

	tglx