Messages in this thread | | | Date | Tue, 11 Dec 2018 13:16:25 +0800 | From | Peter Xu <> | Subject | Re: [PATCH] userfaultfd: clear flag if remap event not enabled |
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On Mon, Dec 10, 2018 at 03:09:25PM -0500, Andrea Arcangeli wrote: > Hello, > > On Mon, Dec 10, 2018 at 07:51:16PM +0200, Mike Rapoport wrote: > > On Mon, Dec 10, 2018 at 02:51:21PM +0800, Peter Xu wrote: > > > When the process being tracked do mremap() without > > > UFFD_FEATURE_EVENT_REMAP on the corresponding tracking uffd file > > > handle, we should not generate the remap event, and at the same > > > time we should clear all the uffd flags on the new VMA. Without > > > this patch, we can still have the VM_UFFD_MISSING|VM_UFFD_WP > > > flags on the new VMA even the fault handling process does not > > > even know the existance of the VMA. > > > > > > CC: Andrea Arcangeli <aarcange@redhat.com> > > > CC: Andrew Morton <akpm@linux-foundation.org> > > > CC: Mike Rapoport <rppt@linux.vnet.ibm.com> > > > CC: Kirill A. Shutemov <kirill@shutemov.name> > > > CC: Hugh Dickins <hughd@google.com> > > > CC: Pavel Emelyanov <xemul@virtuozzo.com> > > > CC: Pravin Shedge <pravin.shedge4linux@gmail.com> > > > CC: linux-mm@kvack.org > > > CC: linux-kernel@vger.kernel.org > > > Signed-off-by: Peter Xu <peterx@redhat.com> > > > --- > > > fs/userfaultfd.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > > > index cd58939dc977..798ae8a438ff 100644 > > > --- a/fs/userfaultfd.c > > > +++ b/fs/userfaultfd.c > > > @@ -740,6 +740,9 @@ void mremap_userfaultfd_prep(struct vm_area_struct *vma, > > > vm_ctx->ctx = ctx; > > > userfaultfd_ctx_get(ctx); > > > WRITE_ONCE(ctx->mmap_changing, true); > > > + } else if (ctx) { > > > + vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; > > > + vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING); > > Great catch Peter! > > > > > My preference would be > > > > if (!ctx) > > return; > > > > if (ctx->features & UFFD_FEATURE_EVENT_REMAP) { > > ... > > } else { > > ... > > } > > > > but I don't feel strongly about it. > > Yes, it'd look nicer to run a single "ctx not null" check.
I agree.
> > > > > I'd appreciate a comment in the code and with it > > > > Acked-by: Mike Rapoport <rppt@linux.ibm.com> > > > > Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Thanks to both! I'll repost soon.
Regards,
-- Peter Xu
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