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

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Message-ID: <87r150bi0d.fsf@redhat.com>
Date:   Wed, 11 May 2022 10:17:22 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Jason Wang <jasowang@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     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, 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.