linux-kernel - Re: [RFC] genirq: Flush the irq thread on synchronization

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Date:	Thu, 1 Mar 2012 12:54:47 +0200
From:	Ido Yariv <ido@...ery.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [RFC] genirq: Flush the irq thread on synchronization

Hi Thomas,

On Wed, Feb 15, 2012 at 03:34:11PM +0100, Thomas Gleixner wrote:
> On Mon, 13 Feb 2012, Ido Yariv wrote:
> 
> > Hi Thomas,
> > 
> > On Sun, Dec 04, 2011 at 09:09:32PM +0200, Ido Yariv wrote:
> > > Hi Thomas,
> > > 
> > > On Sat, Dec 03, 2011 at 12:21:46AM +0100, Thomas Gleixner wrote:
> > > > I can see your problem, but this might lead to threads_active leaks
> > > > under certain conditions. desc->threads_active was only meant to deal
> > > > with shared interrupts.
> > > > 
> > > > We explicitely allow a design where the primary handler can leave the
> > > > device interrupt enabled and allow further interrupts to occur while
> > > > the handler is running. We only have a single bit to note that the
> > > > thread should run, but your wakeup would up the threads_active count
> > > > in that scenario several times w/o a counterpart which decrements it.
> > > > 
> > > > The solution for this is to keep the current threads_active semantics
> > > > and make the wait function different. Instead of waiting for
> > > > threads_active to become 0 it should wait for threads_active == 0 and
> > > > the IRQTF_RUNTHREAD for all actions to be cleared. To avoid looping
> > > > over the actions, we can take a similar approach as we take with the
> > > > desc->threads_oneshot bitfield.
> > > 
> > > Thanks for reviewing this.
> > > 
> > > I might be missing something, but I don't see any potential
> > > threads_active leaks in this approach. We wont increase threads_active
> > > if IRQTF_RUNTHREAD was already set beforehand (as test_and_set_bit()
> > > will return 1).
> > > 
> > > If irq_wake_thread is called multiple times before irq_thread has had a
> > > chance to run, threads_active will only be increased once and decreased
> > > back when IRQTF_RUNTHREAD is cleared.
> > > 
> > > Am I missing something? If not, do you see any other issues with this
> > > implementation?
> > 
> > Any thoughts on this?
> 
> Sorry, went of my radar. Will have a look later today.

Have you had a chance to look into this?

Thanks,
Ido.
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