linux-kernel - Re: [PATCH 2/2] virtio-rng: fix stuck in catting hwrng attributes

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Date:	Tue, 16 Sep 2014 08:50:03 +0800
From:	Amos Kong <akong@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
	amit.shah@...hat.com, jasowang@...hat.com,
	linux-kernel@...r.kernel.org, m@...s.ch,
	herbert@...dor.apana.org.au, mpm@...enic.com
Subject: Re: [PATCH 2/2] virtio-rng: fix stuck in catting hwrng attributes

CC linux-kernel

Original thread: http://comments.gmane.org/gmane.linux.kernel.virtualization/22775

On Mon, Sep 15, 2014 at 06:48:46PM +0200, Radim Krčmář wrote:
> 2014-09-14 10:25+0800, Amos Kong:
> > On Sun, Sep 14, 2014 at 09:12:08AM +0800, Amos Kong wrote:
> > 
> > ...
> > > > > > diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> > > > > > index c591d7e..b5d1b6f 100644
> > > > > > --- a/drivers/char/hw_random/core.c
> > > > > > +++ b/drivers/char/hw_random/core.c
> > > > > > @@ -195,8 +195,7 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf,
> > > > > >  
> > > > > >  		mutex_unlock(&rng_mutex);
> > > > > >  
> > > > > > -		if (need_resched())
> > > > > > -			schedule_timeout_interruptible(1);
> > > > > > +		schedule_timeout_interruptible(10);
> 
> If cond_resched() does not work, it is a bug elsewehere.

Thanks for your reply, Jason also told me the TIF_NEED_RESCHED should
be set in this case, then need_resched() returns true.

I will investigate the issue and reply you later.
 
> > Problem only occurred in non-smp guest, we can improve it to:
> > 
> >                         if(!is_smp())
> >                                 schedule_timeout_interruptible(10);
> > 
> > is_smp() is only available for arm arch, we need a general one.
> 
> (It is num_online_cpus() > 1.)

-- 
			Amos.
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