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

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Date:   Mon, 16 May 2022 13:20:06 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Cornelia Huck <cohuck@...hat.com>, mst <mst@...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>,
        Halil Pasic <pasic@...ux.ibm.com>
Subject: Re: [PATCH V4 0/9] rework on the IRQ hardening of virtio

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.

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

Regards,
Halil

> 
> Thanks