Messages in this thread | | | Date | Tue, 16 Jul 2013 14:43:15 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 1/3] mm: shift VM_GROWS* check from mmap_region() to do_mmap_pgoff() |
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On Sun, 14 Jul 2013 18:54:51 +0200 Oleg Nesterov <oleg@redhat.com> wrote:
> mmap() doesn't allow the non-anonymous mappings with VM_GROWS* bit set. > In particular this means that mmap_region()->vma_merge(file, vm_flags) > must always fail if vm_flags & VM_GROWS. So it does not make sense to > check VM_GROWS* after we already allocated the new vma, the only caller, > do_mmap_pgoff(), which can pass this flag can do the check itself. > > And this looks a bit more correct, mmap_region() already unmapped the > old mapping at this stage. But if mmap() is going to fail, it should > avoid do_munmap() if possible. > > ... > > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -1327,6 +1327,9 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr, > } > } > > + /* Only MAP_PRIVATE|MAP_ANONYMOUS can use MAP_GROWS */ > + if ((vm_flags & VM_MAYSHARE) && (vm_flags & (VM_GROWSDOWN|VM_GROWSUP)))
That is of course vm_flags&(VM_MAYSHARE|VM_GROWSDOWN|VM_GROWSUP), but that perhaps is less clear.
> + return -EINVAL;
I had to stare for a while but yes, the change looks OK to me.
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