linux-kernel - Re: [PATCH 2/3] afs: Fix afs_write

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Message-ID: <YMd5BqIKucO6rW4R@casper.infradead.org>
Date:   Mon, 14 Jun 2021 16:43:02 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     jlayton@...nel.org, linux-afs@...ts.infradead.org,
        ceph-devel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] afs: Fix afs_write_end() to handle short writes

On Mon, Jun 14, 2021 at 04:38:21PM +0100, David Howells wrote:
> Matthew Wilcox <willy@...radead.org> wrote:
> 
> > > -	ASSERT(PageUptodate(page));
> > > -
> > >  	if (PagePrivate(page)) {
> > >  		priv = page_private(page);
> > >  		f = afs_page_dirty_from(page, priv);
> > 
> > Why are you removing this assertion?  Does AFS now support dirty,
> > partially-uptodate pages?  If so, a subsequent read() to that
> > page is going to need to be careful to only read the parts of the page
> > from the server that haven't been written ...
> 
> Because the previous hunk in the patch:
> 
> 	+	if (!PageUptodate(page)) {
> 	+		if (copied < len) {
> 	+			copied = 0;
> 	+			goto out;
> 	+		}
> 	+
> 	+		SetPageUptodate(page);
> 	+	}
> 
> means you can't get there unless PageUptodate() is true by that point.

Isn't the point of an assertion to check that this is true?