linux-kernel - Re: linux-next: build warning after merge of the random tree

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Date:   Tue, 10 Mar 2020 12:17:47 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Theodore Ts'o <tytso@....edu>
Cc:     Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: build warning after merge of the random tree

On Fri, Mar 06, 2020 at 03:53:48PM +1100, Stephen Rothwell wrote:
> Hi all,
> 
> On Mon, 2 Mar 2020 14:44:52 +1100 Stephen Rothwell <sfr@...b.auug.org.au> wrote:
> >
> > After merging the random tree, today's linux-next build (x86_64
> > allnoconfig) produced this warning:
> > 
> > drivers/char/random.c:820:13: warning: 'crng_initialize_secondary' defined but not used [-Wunused-function]
> >   820 | static void crng_initialize_secondary(struct crng_state *crng)
> >       |             ^~~~~~~~~~~~~~~~~~~~~~~~~
> > 
> > Introduced by commit
> > 
> >   5cbe0f13b51a ("random: split primary/secondary crng init paths")
> 
> I am still getting this warning.

Sorry, this is my bad.

We only call crng_initialize_secondary() in do_numa_crng_init(), which
is only built for CONFIG_NUMA. We can either drop both
crng_initialize_secondary() and crng_init_try_arch() under the
CONFIG_NUMA ifdef, or add __maybe_unused to crng_initialize_secondary().

Ted, does the below look ok to you? Or would you prefer moving things
under the ifdeffery?

Thanks,
Mark.

---->8----
>From 6c3a35cd562d53066e11f5f8a6c3a6f63701d3ed Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland@....com>
Date: Tue, 10 Mar 2020 12:09:12 +0000
Subject: [PATCH] random: avoid warnings for !CONFIG_NUMA builds

As crng_initialize_secondary() is only called by do_numa_crng_init(),
and the latter is under ifdeffery for CONFIG_NUMA, when CONFIG_NUMA is
not selected the compiler will warn that the former is unused:

| drivers/char/random.c:820:13: warning: 'crng_initialize_secondary' defined but not used [-Wunused-function]
|   820 | static void crng_initialize_secondary(struct crng_state *crng)
|       |             ^~~~~~~~~~~~~~~~~~~~~~~~~

Stephen reports that this happens for x86_64 noallconfig builds.

We could move crng_initialize_secondary() and crng_init_try_arch() under
the CONFIG_NUMA ifdeffery, but this has the unfortunate property of
separating them from crng_initialize_primary() and
crng_init_try_arch_early() respectively. Instead, let's mark
crng_initialize_secondary() as __maybe_unused.

Fixes: 5cbe0f13b51a ("random: split primary/secondary crng init paths")
Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: Theodore Ts'o <tytso@....edu>
---
 drivers/char/random.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index f43f65c2195d..0d10e31fd342 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -817,7 +817,7 @@ static bool __init crng_init_try_arch_early(struct crng_state *crng)
 	return arch_init;
 }
 
-static void crng_initialize_secondary(struct crng_state *crng)
+static void __maybe_unused crng_initialize_secondary(struct crng_state *crng)
 {
 	memcpy(&crng->state[0], "expand 32-byte k", 16);
 	_get_random_bytes(&crng->state[4], sizeof(__u32) * 12);
-- 
2.11.0