On Tue, Jan 31, 2017 at 04:41:32PM -0800, Andrew Morton wrote:

On Fri, 27 Jan 2017 20:44:31 +0200 Mike Rapoport [off-list ref] wrote:

quoted

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?

 
Sure, will add. Do you prefer an incremental patch or update this one?

--
Sincerely yours,
Mike.

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