On 07/21/2016 09:43 PM, Valdis.Kletnieks@vt.edu wrote:
> On Mon, 11 Jul 2016 13:53:36 -0700, Andy Lutomirski said:
>> This avoids pointless races in which another CPU or task might see a
>> partially populated global pgd entry.  These races should normally
>> be harmless, but, if another CPU propagates the entry via
>> vmalloc_fault and then populate_pgd fails (due to memory allocation
>> failure, for example), this prevents a use-after-free of the pgd
>> entry.
>>
>> Signed-off-by: Andy Lutomirski <luto@kernel.org>
>> ---
>>  arch/x86/mm/pageattr.c | 9 ++++++---
>>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> I just bisected a failure to boot down to this patch.  On my Dell Latitude
> laptop, it results in the kernel being loaded and then just basically sitting
> there dead in the water - as far as I can tell, it dies before the kernel
> ever gets going far enough to do any console I/O (even with ignore_loglevel).
> Nothing in /sys/fs/pstore either.  I admit not understanding the VM code
> at all, so I don't have a clue *why* this causes indigestion...
>
> CPU is an Intel Core i5-3340M in case that matters....
>

How much memory do you have and what's your config?  My code is 
obviously buggy, but I'm wondering why neither I nor the 0day bot caught 
this.

The attached patch is compile-tested only.  (Even Thunderbird doesn't 
want to send non-flowed text right now, sigh.)

--Andy