Re: [PATCH V4 1/6] mm: mlock: Refactor mlock, munlock, and munlockall code

Eric B Munson
2015-07-22T14:04:47Z

[-- Attachment #1: Type: text/plain, Size: 1257 bytes --]

On Wed, 22 Jul 2015, Kirill A. Shutemov wrote:

> On Tue, Jul 21, 2015 at 03:59:36PM -0400, Eric B Munson wrote:
> > @@ -648,20 +656,23 @@ SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
> > start &= PAGE_MASK;
> >
> > down_write(&current->mm->mmap_sem);
> > - ret = do_mlock(start, len, 0);
> > + ret = apply_vma_flags(start, len, flags, false);
> > up_write(&current->mm->mmap_sem);
> >
> > return ret;
> > }
> >
> > +SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
> > +{
> > + return do_munlock(start, len, VM_LOCKED);
> > +}
> > +
> > static int do_mlockall(int flags)
> > {
> > struct vm_area_struct * vma, * prev = NULL;
> >
> > if (flags & MCL_FUTURE)
> > current->mm->def_flags |= VM_LOCKED;
> > - else
> > - current->mm->def_flags &= ~VM_LOCKED;
>
> I think this is wrong.
>
> With current code mlockall(MCL_CURRENT) after mlockall(MCL_FUTURE |
> MCL_CURRENT) would undo future mlocking, without unlocking currently
> mlocked memory.
>
> The change will break the use-case.

It is wrong and I have addressed it in this case as well as with the
MCL_ONFAULT flag introduced in patch 4. I will also add to the mlockall
man page to specify this behavior.

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 819 bytes --]