Re: [PATCH 01/13] mm: Add AOP_UPDATED_PAGE return value

Matthew Wilcox
2020-09-17T22:04:02Z

On Thu, Sep 17, 2020 at 04:10:38PM +0100, Matthew Wilcox (Oracle) wrote:
> +++ b/mm/filemap.c
> @@ -2254,8 +2254,10 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
> * PG_error will be set again if readpage fails.
> */
> ClearPageError(page);
> - /* Start the actual read. The read will unlock the page. */
> + /* Start the actual read. The read may unlock the page. */
> error = mapping->a_ops->readpage(filp, page);
> + if (error == AOP_UPDATED_PAGE)
> + goto page_ok;
>
> if (unlikely(error)) {
> if (error == AOP_TRUNCATED_PAGE) {

If anybody wants to actually test this, this hunk is wrong.

+++ b/mm/filemap.c
@@ -2256,8 +2256,11 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
ClearPageError(page);
/* Start the actual read. The read may unlock the page. */
error = mapping->a_ops->readpage(filp, page);
- if (error == AOP_UPDATED_PAGE)
+ if (error == AOP_UPDATED_PAGE) {
+ unlock_page(page);
+ error = 0;
goto page_ok;
+ }

if (unlikely(error)) {
if (error == AOP_TRUNCATED_PAGE) {

> @@ -2619,7 +2621,7 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
> */
> if (unlikely(!PageUptodate(page)))
> goto page_not_uptodate;
> -
> +page_ok:
> /*
> * We've made it this far and we had to drop our mmap_lock, now is the
> * time to return to the upper layer and have it re-find the vma and
> @@ -2654,6 +2656,8 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
> ClearPageError(page);
> fpin = maybe_unlock_mmap_for_io(vmf, fpin);
> error = mapping->a_ops->readpage(file, page);
> + if (error == AOP_UPDATED_PAGE)
> + goto page_ok;
> if (!error) {
> wait_on_page_locked(page);
> if (!PageUptodate(page))
> @@ -2867,6 +2871,10 @@ static struct page *do_read_cache_page(struct address_space *mapping,
> err = filler(data, page);
> else
> err = mapping->a_ops->readpage(data, page);
> + if (err == AOP_UPDATED_PAGE) {
> + unlock_page(page);
> + goto out;
> + }
>
> if (err < 0) {
> put_page(page);
> --
> 2.28.0
>