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

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Date:	Wed, 31 Oct 2012 23:36:06 +0900
From:	anish kumar <anish198519851985@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
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 10:15 -0400, Steven Rostedt wrote:
> 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().
Oh I didn't see that logic properly and rightly pointed out by you, we
should _just_ return instead of queuing the work if the state was
already pending.
> 
> -- Steve
> 
> >  	__irq_work_queue(work);
> >  	return true;
> >  }
> 
> 


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