Re: [PATCH] mm: fix incorrect behavior when process virtual address space limit is exceeded

From: Oleg Nesterov
Date: Tue Nov 17 2015 - 10:23:37 EST

On 11/16, Piotr Kwapulinski wrote:
> @@ -1551,7 +1552,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
> * MAP_FIXED may remove pages of mappings that intersects with
> * requested mapping. Account for the pages it would unmap.
> */
> - if (!(vm_flags & MAP_FIXED))
> + if (!(flags & MAP_FIXED))
> return -ENOMEM;

Agree, "vm_flags & MAP_FIXED" makes no sense and just wrong...

Can't we simply remove this check? Afaics it only helps to avoid
count_vma_pages_range() in the unlikely case when may_expand_vm() fails.
And without MAP_FIXED count_vma_pages_range() should be cheap,
find_vma_intersection() should fail.

And afaics arch/tile/mm/elf.c can use do_mmap(MAP_FIXED ...) rather than
mmap_region(), it can be changed by a separate patch. In this case we can
unexport mmap_region().

OTOH, I won't insist, this patch looks fine to me.


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