Messages in this thread | | | Date | Wed, 15 Jul 2020 23:55:08 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCHv2] mm: Fix warning in move_normal_pmd() |
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On Wed, Jul 15, 2020 at 11:36:59AM -0700, Linus Torvalds wrote: > On Wed, Jul 15, 2020 at 6:50 AM Kirill A. Shutemov > <kirill.shutemov@linux.intel.com> wrote: > > > > mremap(2) does not allow source and destination regions to overlap, but > > shift_arg_pages() calls move_page_tables() directly and in this case the > > source and destination overlap often. It > > Actually, before we do this patch (which I think is a good idea), I'd > like Naresh to test the attached patch. > > And Kirill, Joel, mind looking it over too.
I don't understand 'len' calculation in try_to_align_end().
IIUC, it increases 'len' by PMD_SIZE if 'new_addr+len' is not aligned to PMD_SIZE. It doesn't make sense to me.
Maybe *len = roundup_up(*new_addr + *len, PMD_SIZE) - *new_addr;
or something?
BUT
I *think* there's a bigger problem with the patch:
For stack relocation case both VMAs are the same and always(?) the only VMA around at the time. It means none of ADDR_BEFORE_PREV and ADDR_AFTER_NEXT are going to stop us.
Consider the following case, before and after try_to_align_start():
before after old_addr: 0x0123000 0x0000000 new_addr: 0x1123000 0x1000000 len: 0x1000000 0x1123000
(4k PAGE_SIZE, 2M PMD_SIZE)
On the first iteration we would attempt to move 0x0-0x200000 to 0x1000000-0x1200000 and step onto the same WARN(), no?
-- Kirill A. Shutemov
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