linux-kernel - Re: [PATCH v2 1/2] nfit: Fix the abuse of COMPLETION_INITIALIZER

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Date:   Fri, 25 Aug 2017 08:18:10 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, walken@...gle.com,
        Byungchul Park <byungchul.park@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>, willy@...radead.org,
        Nicholas Piggin <npiggin@...il.com>, kernel-team@....com,
        Dan Williams <dan.j.williams@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, linux-nvdimm@...ts.01.org,
        linux-acpi@...r.kernel.org
Subject: Re: [PATCH v2 1/2] nfit: Fix the abuse of
 COMPLETION_INITIALIZER_ONSTACK()

On Thu, Aug 24, 2017 at 10:22:36PM +0800, Boqun Feng wrote:
> COMPLETION_INITIALIZER_ONSTACK() is supposed to used as an initializer,
> in other words, it should only be used in assignment expressions or
> compound literals. So the usage in drivers/acpi/nfit/core.c:
> 
> 	COMPLETION_INITIALIZER_ONSTACK(flush.cmp);
> 
> , is inappropriate.
> 
> Besides, this usage could also break compilations for another fix to
> reduce stack sizes caused by COMPLETION_INITIALIZER_ONSTACK(), because
> that fix changes COMPLETION_INITIALIZER_ONSTACK() from rvalue to lvalue,
> and usage as above will report error:
> 
> 	drivers/acpi/nfit/core.c: In function 'acpi_nfit_flush_probe':
> 	include/linux/completion.h:77:3: error: value computed is not used [-Werror=unused-value]
> 	  (*({ init_completion(&work); &work; }))
> 
> This patch fixes this by replacing COMPLETION_INITIALIZER_ONSTACK() with
> init_completion() in acpi_nfit_flush_probe(), which does the same
> initialization without any other problem.
> 
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> ---

Sorry, forget to metion:

v1 --> v2:
	Improve the commit log, based on Dan, Thomas and Arnd's
	comments.

Only V2 of this patch #1 is updated. 

Regards,
Boqun

>  drivers/acpi/nfit/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
> index 19182d091587..1893e416e7c0 100644
> --- a/drivers/acpi/nfit/core.c
> +++ b/drivers/acpi/nfit/core.c
> @@ -2884,7 +2884,7 @@ static int acpi_nfit_flush_probe(struct nvdimm_bus_descriptor *nd_desc)
>  	 * need to be interruptible while waiting.
>  	 */
>  	INIT_WORK_ONSTACK(&flush.work, flush_probe);
> -	COMPLETION_INITIALIZER_ONSTACK(flush.cmp);
> +	init_completion(&flush.cmp);
>  	queue_work(nfit_wq, &flush.work);
>  	mutex_unlock(&acpi_desc->init_mutex);
>  
> -- 
> 2.14.1
> 

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