linux-kernel - Re: [patch V2 2/6] genirq: Fix misleading synchronize

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Date:   Mon, 1 Jul 2019 20:23:11 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Marc Zyngier <marc.zyngier@....com>
Subject: Re: [patch V2 2/6] genirq: Fix misleading synchronize_irq()
 documentation

On Mon, Jul 01, 2019 at 08:01:24PM +0200, Thomas Gleixner wrote:
> On Mon, 1 Jul 2019, Peter Zijlstra wrote:
> 
> > On Fri, Jun 28, 2019 at 01:11:50PM +0200, Thomas Gleixner wrote:
> > > The function might sleep, so it cannot be called from interrupt
> > > context. Not even with care.
> > > 
> > > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > > ---
> > >  kernel/irq/manage.c |    3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > --- a/kernel/irq/manage.c
> > > +++ b/kernel/irq/manage.c
> > > @@ -96,7 +96,8 @@ EXPORT_SYMBOL(synchronize_hardirq);
> > >   *	to complete before returning. If you use this function while
> > >   *	holding a resource the IRQ handler may need you will deadlock.
> > >   *
> > > - *	This function may be called - with care - from IRQ context.
> > > + *	Can only be called from preemptible code as it might sleep when
> > > + *	an interrupt thread is associated to @irq.
> > >   */
> > >  void synchronize_irq(unsigned int irq)
> > >  {
> > 
> > +	might_sleep();
> > 
> > ?
> 
>   ....
> 
> 	wait_event()
> 	  might_sleep() ...
> 

That's conditional on desc, but sure, that should work in most sane
cases.