On 2019/3/7 下午11:34, Michael S. Tsirkin wrote:
On Thu, Mar 07, 2019 at 10:45:57AM +0800, Jason Wang wrote:
On 2019/3/7 上午12:31, Michael S. Tsirkin wrote:
+static void vhost_set_vmap_dirty(struct vhost_vmap *used)
+{
+ int i;
+
+ for (i = 0; i < used->npages; i++)
+ set_page_dirty_lock(used->pages[i]);
This seems to rely on page lock to mark page dirty.
Could it happen that page writeback will check the
page, find it clean, and then you mark it dirty and then
invalidate callback is called?
Yes. But does this break anything?
The page is still there, we just remove a
kernel mapping to it.
Thanks
Yes it's the same problem as e.g. RDMA:
we've just marked the page as dirty without having buffers.
Eventually writeback will find it and filesystem will complain...
So if the pages are backed by a non-RAM-based filesystem, it’s all just
broken.
Yes, we can't depend on the pages that might have been invalidated. As
suggested, the only suitable place is the MMU notifier callbacks.
Thanks
one can hope that RDMA guys will fix it in some way eventually.
For now, maybe add a flag in e.g. VMA that says that there's no
writeback so it's safe to mark page dirty at any point?
