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

[Matthew Wilcox]

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
>