linux-kernel - Re: linux-next: manual merge of the mm-stable tree with the cifs tree

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Message-ID: <Y/TbYGXC4HKunymf@casper.infradead.org>
Date:   Tue, 21 Feb 2023 14:55:28 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        "Vishal Moola (Oracle)" <vishal.moola@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steve French <smfrench@...il.com>,
        Steve French <stfrench@...rosoft.com>,
        Shyam Prasad N <nspmangalore@...il.com>,
        Rohith Surabattula <rohiths.msft@...il.com>,
        Tom Talpey <tom@...pey.com>, Paulo Alcantara <pc@....nz>,
        Jeff Layton <jlayton@...nel.org>, linux-cifs@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-next@...r.kernel.org
Subject: Re: linux-next: manual merge of the mm-stable tree with the cifs tree

On Tue, Feb 21, 2023 at 02:39:24PM +0000, David Howells wrote:
> -		folio = page_folio(head_page);
> -		start = folio_pos(folio); /* May regress with THPs */
> +		for (i = 0; i < n; i++) {
> +			folio = fbatch.folios[i];
> +			start = folio_pos(folio); /* May regress with THPs */

What does this comment mean?

> +			/* At this point we hold neither the i_pages lock nor the
> +			 * page lock: the page may be truncated or invalidated
> +			 * (changing page->mapping to NULL), or even swizzled
> +			 * back from swapper_space to tmpfs file mapping

Where does this comment come from?  This is cifs, not tmpfs.  You'll
never be asked to writeback a page from the swap cache.  Dirty pages
can be truncated, so the first half of the comment is still accurate.
I'd rather it moved down to below the folio lock, and was rephrased
so it described why we're checking everything again.

The actual code looks right.