On Tue, Sep 24, 2013 at 01:41:00PM +0900, Inki Dae wrote: > I can't see to hold ->mmap_sem when it calls find_vma() anywhere else. Er... What, in your opinion, would protect the result of find_vma(), if not that? E.g. if another thread does munmap() on that area... vma isn't refcounted; there are only two things that can prevent its freeing - mmap_sem being held and the lack of anybody else seeing the address of mm_struct it belongs to (basically, when we are killing mm_struct off or when we are populating a fresh mm_struct; in the latter case the parent is locked, but the child doesn't need to). Look at page fault handlers - they grab mmap_sem (shared) before looking for vma. And anything modifying the list of vmas (vm_mmap(), etc.) grabs it exclusive... > > to caller) and clones it manually, regardless of whether that vma allows > > to clone itself or not. Quite a few drivers rely on that not happening... > > > > I think that has no any problem because exynos_gem_get_vma() takes a > reference to vma, and also v4l2 side is using same way. I and v4l2 guys > might be missing something what you are concerning. So Could you give us > more comments? vb2_get_vma()/vb2_put_userptr() is also buggy. At the very least, it should refuse to handle ones with VM_DONTCOPY in flags. Again, there are drivers that seriously rely on VM_DONTCOPY being honoured. BTW, what do you expect exynos_gem_get_pages_from_userptr() to do if the area has been unmapped in the meanwhile? Or, for that matter, if that has been followed by mmap() of something with VM_IO on the same range of addresses... ->open() does *NOT* prevent any of that. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
