Re: [PATCH] mm/filemap.c: clear page error before actual read

[田 <xianting_tian@xxxxxxx>]

hi Wilcox
thanks for your reply:)
totally agree, it is more accurate as below, I will send the patch again, thanks.
+ ClearPageError(page);
  goto filler;


On 03/04/2020 00:43, Matthew Wilcox wrote:
On Tue, Mar 03, 2020 at 10:09:50AM -0500, Xianting Tian wrote:
> This patch is to add the calling of ClearPageError just before the
> actual read of read path of cramfs mount.

Thank you for your patch and your analysis.  I concur; an error set
on a page will not be cleared by doing a subsequent read.  This is
probably an oversight; in generic_file_buffered_read(), we do:

               ClearPageError(page);
               /* Start the actual read. The read will unlock the page. */
               error = mapping->a_ops->readpage(filp, page);

and also in filemap_fault:

       ClearPageError(page);
       fpin = maybe_unlock_mmap_for_io(vmf, fpin);
       error = mapping->a_ops->readpage(file, page);

That said, a freshly allocated page will not have PageError set on
it, so I would prefer to see this:

       /* Someone else locked and filled the page in a very small window */
       if (PageUptodate(page)) {
               unlock_page(page);
               goto out;
       }
+     ClearPageError(page);
       goto filler;