linux-kernel - Re: [PATCH] module: silence warning about unused 'no

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Message-ID: <2024032224-equator-calm-5f3a@gregkh>
Date: Fri, 22 Mar 2024 14:47:03 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Luis Chamberlain <mcgrof@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	linux-modules@...r.kernel.org,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] module: silence warning about unused 'no_warn' variable

On Fri, Mar 22, 2024 at 02:20:05PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> The sysfs_create_link() return code is marked as __must_check, but the
> module_add_driver() function tries hard to not care, by assigning the
> return code to a variable. When building with 'make W=1', gcc still
> warns because this variable is only assigned but not used:
> 
> drivers/base/module.c: In function 'module_add_driver':
> drivers/base/module.c:36:6: warning: variable 'no_warn' set but not used [-Wunused-but-set-variable]
> 
> Add an explicit cast to void to prevent this check as well.
> 
> Cc: Luis Chamberlain <mcgrof@...nel.org>
> Cc: linux-modules@...r.kernel.org
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Fixes: e17e0f51aeea ("Driver core: show drivers in /sys/module/")
> See-also: 4a7fb6363f2d ("add __must_check to device management code")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> I'm not entirely sure what bug the __must_check on sysfs_create_link()
> is trying to prevent, or why the module loader code is allowed to
> ignore this. It would be nice to have an Ack from the sysfs maintainers
> on this.

No, let's fix this properly and unwind if we can't create the link.  You
are pointing at something from 2006, so I guess we always thought "this
can not fail" and never did anything about it since then.

thanks,

greg k-h