On Wed, Aug 22, 2018 at 01:45:44PM -0700, Yang Shi wrote: > > > On 8/22/18 4:19 AM, Vlastimil Babka wrote: > > On 08/15/2018 08:49 PM, Yang Shi wrote: > > > + downgrade_write(&mm->mmap_sem); > > > + > > > + /* Zap mappings with read mmap_sem */ > > > + unmap_region(mm, start_vma, prev, start, end); > > > + > > > + arch_unmap(mm, start_vma, start, end); > > Hmm, did you check that all architectures' arch_unmap() is safe with > > read mmap_sem instead of write mmap_sem? E.g. x86 does > > mpx_notify_unmap() there where I would be far from sure at first glance... > > Yes, I'm also not quite sure if it is 100% safe or not. I was trying to move > this before downgrade_write, however, I'm not sure if it is ok or not too, > so I keep the calling sequence. > > For architectures, just x86 and ppc really do something. PPC just uses it > for vdso unmap which should just happen during process exit, so it sounds > safe. > > For x86, mpx_notify_unmap() looks finally zap the VM_MPX vmas in bound table > range with zap_page_range() and doesn't update vm flags, so it sounds ok to > me since vmas have been detached, nobody can find those vmas. But, I'm not > familiar with the details of mpx, maybe Kirill could help to confirm this? I don't see anything obviously dependent on down_write() in mpx_notify_unmap(), but Dave should know better. -- Kirill A. Shutemov
