Re: [lkp-robot] [x86/cpu_entry_area] 10043e02db: kernel_BUG_at_arch/x86/mm/physaddr.c

[Dmitry Vyukov]

On Thu, Dec 28, 2017 at 12:51 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> On Wed, 27 Dec 2017, Dmitry Vyukov wrote:
>> On Wed, Dec 27, 2017 at 7:05 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> 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. I will cook a patch (if Andrey won't beat me to it).