Hello Andrew,
On Tue, Jan 31, 2017 at 04:41:32PM -0800, Andrew Morton wrote:
> On Fri, 27 Jan 2017 20:44:31 +0200 Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> wrote:
>
> > Allow userfaultfd monitor track termination of the processes that have
> > memory backed by the uffd.
> >
> > --- a/fs/userfaultfd.c
> > +++ b/fs/userfaultfd.c
> > @@ -774,6 +774,30 @@ void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
> > }
> > }
> >
> > +void userfaultfd_exit(struct mm_struct *mm)
> > +{
> > + struct vm_area_struct *vma = mm->mmap;
> > +
> > + while (vma) {
> > + struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
> > +
> > + if (ctx && (ctx->features & UFFD_FEATURE_EVENT_EXIT)) {
> > + struct userfaultfd_wait_queue ewq;
> > +
> > + userfaultfd_ctx_get(ctx);
> > +
> > + msg_init(&ewq.msg);
> > + ewq.msg.event = UFFD_EVENT_EXIT;
> > +
> > + userfaultfd_event_wait_completion(ctx, &ewq);
> > +
> > + ctx->features &= ~UFFD_FEATURE_EVENT_EXIT;
> > + }
> > +
> > + vma = vma->vm_next;
> > + }
> > +}
>
> And we can do the vma walk without locking because the caller (exit_mm)
> knows it now has exclusive access. Worth a comment?
I've just used your wording, seems to me neat and to the point.
>From 74af75b062dcb2dc3cc8d2b57f9388c22c2b89e5 Mon Sep 17 00:00:00 2001
From: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Date: Thu, 2 Feb 2017 15:50:14 +0200
Subject: [PATCH] userfaultfd: exit event: add comment about lockless vma walk
Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
---
fs/userfaultfd.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 6587f40..3c421d0 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -778,6 +778,10 @@ void userfaultfd_exit(struct mm_struct *mm)
{
struct vm_area_struct *vma = mm->mmap;
+ /*
+ * We can do the vma walk without locking because the caller
+ * (exit_mm) knows it now has exclusive access
+ */
while (vma) {
struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
--
1.9.1
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