linux-kernel - Re: [PATCH] [RFC]IRQ CORE: irq_work_queue function return value not used.

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Message-ID: <1351692914.4004.83.camel@gandalf.local.home>
Date:	Wed, 31 Oct 2012 10:15:14 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	anish kumar <anish198519851985@...il.com>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org,
	akpm@...ux-foundation.org, paul.gortmaker@...driver.com,
	tglx@...utronix.de, mingo@...nel.org, fweisbec@...il.com
Subject: Re: [PATCH] [RFC]IRQ CORE: irq_work_queue function return value not
 used.

On Wed, 2012-10-31 at 23:02 +0900, anish kumar wrote:
> From: anish kumar <anish198519851985@...il.com>
> 
> As no one is using the return value of irq_work_queue function
> it is better to just make it void.
> 
> This patch is just a way to understand if there is some future
> plan to use it but in any case please let me know the reason.
> ---
>  kernel/irq_work.c |   21 ++++++++++-----------
>  1 files changed, 10 insertions(+), 11 deletions(-)
> 
> diff --git a/kernel/irq_work.c b/kernel/irq_work.c
> index 1588e3b..4a9a44c 100644
> --- a/kernel/irq_work.c
> +++ b/kernel/irq_work.c
> @@ -32,21 +32,21 @@ static DEFINE_PER_CPU(struct llist_head, irq_work_list);
>  /*
>   * Claim the entry so that no one else will poke at it.
>   */
> -static bool irq_work_claim(struct irq_work *work)
> +static void irq_work_claim(struct irq_work *work)
>  {
>  	unsigned long flags, nflags;
>  
>  	for (;;) {
>  		flags = work->flags;
>  		if (flags & IRQ_WORK_PENDING)
> -			return false;
> +			return;
>  		nflags = flags | IRQ_WORK_FLAGS;
>  		if (cmpxchg(&work->flags, flags, nflags) == flags)
>  			break;
>  		cpu_relax();
>  	}
>  
> -	return true;
> +	return;
>  }
>  
>  void __weak arch_irq_work_raise(void)
> @@ -79,15 +79,14 @@ static void __irq_work_queue(struct irq_work *work)
>   *
>   * Can be re-enqueued while the callback is still in progress.
>   */
> -bool irq_work_queue(struct irq_work *work)
> +void irq_work_queue(struct irq_work *work)
>  {
> -	if (!irq_work_claim(work)) {
> -		/*
> -		 * Already enqueued, can't do!
> -		 */
> -		return false;
> -	}
> -
> +	/*
> +	 * This function either will claim the entry to queue
> +	 * the work or if the work is already queued and is in
> +	 * pending state then it will simply return.
> +	 */
> +	irq_work_claim(work)

Um, no.

If the state was already pending, we will corrupt the llist node of the
work if we call irq_work_queue(). You must check the return value of
irq_work_claim() and return if it fails. You can not call
__irq_work_queue() if irq_work_claim() does not succeed.

The return value of irq_work_queue() can be ignored, but not
irq_work_claim().

-- Steve

>  	__irq_work_queue(work);
>  	return true;
>  }


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