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

From: Oleg Nesterov
Date: Tue Nov 17 2015 - 10:37:54 EST

On 11/17, Oleg Nesterov wrote:
> 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.

Or we can simply move this may_expand_vm() block to the caller, do_mmap().

> 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.

Yes, but what I actually tried to say is that it would be nice to unexport
mmap_region(), arch/tile is the only caller outside of mmap.c.


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