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Subject: Re: [PATCH 4/9] drm/xen-front: Implement Xen event channel handling
To:     Oleksandr Andrushchenko <andr2000@gmail.com>,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, airlied@linux.ie,
        daniel.vetter@intel.com, seanpaul@chromium.org,
        gustavo@padovan.org, jgross@suse.com, konrad.wilk@oracle.com
Cc:     Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
References: <1519200222-20623-1-git-send-email-andr2000@gmail.com>
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 <395cdaef-db7e-139c-bbf1-28cb33f41f58@oracle.com>
 <5145287f-40b0-c8e2-1b37-36d7e8cac908@gmail.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
Message-ID: <7d8ab151-e90d-baef-93b6-8ca1c7e42908@oracle.com>
Date:   Fri, 23 Feb 2018 09:44:43 -0500
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On 02/23/2018 02:00 AM, Oleksandr Andrushchenko wrote:
> On 02/23/2018 01:50 AM, Boris Ostrovsky wrote:
>> On 02/21/2018 03:03 AM, Oleksandr Andrushchenko wrote:
>>> +
>>> +static irqreturn_t evtchnl_interrupt_ctrl(int irq, void *dev_id)
>>> +{
>>> +    struct xen_drm_front_evtchnl *evtchnl = dev_id;
>>> +    struct xen_drm_front_info *front_info = evtchnl->front_info;
>>> +    struct xendispl_resp *resp;
>>> +    RING_IDX i, rp;
>>> +    unsigned long flags;
>>> +
>>> +    spin_lock_irqsave(&front_info->io_lock, flags);
>>> +
>>> +    if (unlikely(evtchnl->state != EVTCHNL_STATE_CONNECTED))
>>> +        goto out;
>> Do you need to check the state under lock? (in other routines too).
> not really, will move out of the lock in interrupt handlers
> other places (I assume you refer to be_stream_do_io)


I was mostly referring to evtchnl_interrupt_evt().

-boris


> it is set under lock as a part of atomic operation, e.g.
> we get a new request pointer from the ring and reset completion
> So, those places still seem to be ok