linux-kernel - Re: [PATCH] mm: Fix compile error when CONFIG

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Message-ID: <20250603102959.20c85adb@gandalf.local.home>
Date: Tue, 3 Jun 2025 10:29:59 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Hugh Dickins <hughd@...gle.com>
Cc: Matthew Wilcox <willy@...radead.org>, LKML
 <linux-kernel@...r.kernel.org>, linux-mm@...ck.org, Andrew Morton
 <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] mm: Fix compile error when CONFIG_SHMEM is not set

On Tue, 3 Jun 2025 01:02:36 -0700 (PDT)
Hugh Dickins <hughd@...gle.com> wrote:

> Agreed that ramfs does not use swap, so calling swap_writepage() would
> be weird.  But, thanks for the build fix Steve, but it cannot be right
> because return 0 says shmem_writeout() successfully sent the page to
> swap, and that has unlocked the page (or soon will do so).  It should
> return an error (-ENXIO?), but I haven't checked what the callers do with

Yeah, I figured it should return an error, but looking at the code I
couldn't figure out what the proper error would be. Then I also noticed
that the other stub functions just returned zero so I did the same.

Perhaps add a WARN_ON_ONCE() if it is called without CONFIG_SHMEM configured?

> that, nor whether they need the folio to be redirtied.  And wouldn't it
> need an EXPORT like the real one?  Sorry, can't keep up, there are many
> many things I should have looked at but have not... Tomorrow?

Yeah, it probably needs an export as well.

Note, if you come up with a solution, by all means use it and don't use my
patch. I'm happy with a "Reported-by" and don't need to be the author. This
is the "fix" I'm using so that I can test my code because without it, my
tests fail.

I'm also happy to send another update if it's simple.

-- Steve