Re: PROBLEM: repeated remap_file_pages on tmpfs triggers bug on process exit

From: Konstantin Khlebnikov
Date: Tue Jul 15 2014 - 07:33:33 EST

On Tue, Jul 15, 2014 at 2:55 PM, Kirill A. Shutemov
<kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> Konstantin Khlebnikov wrote:
>> It seems boundng logic in do_fault_around is wrong:
>> start_addr = max(address & fault_around_mask(), vma->vm_start);
>> off = ((address - start_addr) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1);
>> pte -= off;
>> pgoff -= off;
>> Ok, off <= 511, but it might be bigger than pte offset in pte table.
> I don't see how it possible: fault_around_mask() cannot be more than 0x1ff000
> (x86-64, fault_around_bytes == 2M). It means start_addr will be aligned to 2M
> boundary in this case which is start of the page table pte belong to.
> Do I miss something?

Nope, you're right. This fixes kernel crash but not the original problem.

Problem is caused by calling do_fault_around for _non-linear_ faiult.
In this case pgoff is shifted and might become negative during calculation.
I'll send another patch.

> --
> Kirill A. Shutemov
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at