linux-kernel - Re: [PATCH V4 0/9] rework on the IRQ hardening of virtio

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Message-ID: <20220516102425-mutt-send-email-mst@kernel.org>
Date:   Mon, 16 May 2022 10:25:01 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Halil Pasic <pasic@...ux.ibm.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Marc Zyngier <maz@...nel.org>, eperezma <eperezma@...hat.com>,
        Cindy Lu <lulu@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH V4 0/9] rework on the IRQ hardening of virtio

On Mon, May 16, 2022 at 01:20:06PM +0200, Halil Pasic wrote:
> On Thu, 12 May 2022 11:31:08 +0800
> Jason Wang <jasowang@...hat.com> wrote:
> 
> > > > It looks to me we need to use write_lock_irq()/write_unlock_irq() to
> > > > do the synchronization.
> > > >
> > > > And we probably need to keep the
> > > > read_lock_irqsave()/read_lock_irqrestore() logic since I can see the
> > > > virtio_ccw_int_handler() to be called from process context (e.g from
> > > > the io_subchannel_quiesce()).
> > > >  
> > >
> > > Sounds correct.  
> > 
> > As Cornelia and Vineeth pointed out, all the paths the vring_interrupt
> > is called with irq disabled.
> > 
> > So I will use spin_lock()/spin_unlock() in the next version.
> 
> Can we do some sort of an assertion that if the kernel is built with
> the corresponding debug features will make sure this assumption holds
> (and warn if it does not)? That assertion would also document the fact.

Lockdep will do this automatically if you get it wrong, just like it
did here.

> If an assertion is not possible, I think we should at least place a
> strategic comment that documents our assumption.

That can't hurt.

> Regards,
> Halil
> 
> > 
> > Thanks