linux-kernel - Re: [PATCH V4 6/9] virtio-ccw: implement synchronize

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Message-ID: <CACGkMEtPk9P4KhJ5wTOLj9CZoKDx9-X_5uLRVBag692x4s9SrA@mail.gmail.com>
Date:   Wed, 11 May 2022 16:58:45 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     "Michael S. Tsirkin" <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>,
        Halil Pasic <pasic@...ux.ibm.com>,
        eperezma <eperezma@...hat.com>, Cindy Lu <lulu@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH V4 6/9] virtio-ccw: implement synchronize_cbs()

On Wed, May 11, 2022 at 4:17 PM Cornelia Huck <cohuck@...hat.com> wrote:
>
> On Wed, May 11 2022, Jason Wang <jasowang@...hat.com> wrote:
>
> > On Tue, May 10, 2022 at 7:28 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> >>
> >> On Sat, May 07, 2022 at 03:19:51PM +0800, Jason Wang wrote:
> >> > @@ -1106,6 +1130,7 @@ static void virtio_ccw_int_handler(struct ccw_device *cdev,
> >> >                       vcdev->err = -EIO;
> >> >       }
> >> >       virtio_ccw_check_activity(vcdev, activity);
> >> > +     read_lock_irqsave(&vcdev->irq_lock, flags);
> >> >       for_each_set_bit(i, indicators(vcdev),
> >> >                        sizeof(*indicators(vcdev)) * BITS_PER_BYTE) {
> >> >               /* The bit clear must happen before the vring kick. */
> >>
> >> Cornelia sent a lockdep trace on this.
> >>
> >> Basically I think this gets the irqsave/restore logic wrong.
> >> It attempts to disable irqs in the handler (which is an interrupt
> >> anyway).
> >
> > The reason I use irqsave/restore is that it can be called from process
> > context (if I was not wrong), e.g from io_subchannel_quiesce().
>
> io_subchannel_quiesce() should disable interrupts, though? Otherwise, it
> would be a bug.

Right, it was protected by a spin_lock_irq(), but I can see other
cdev->handler() in e.g device_fsm.c, the irq status is not obvious, do
they have the same assumption which IRQ is disabled?

Thanks

>