linux-kernel - Re: [PATCH] xen/pvcalls-back: fix permanently masked event channel

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Date:   Fri, 20 Jan 2023 08:24:11 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Volodymyr Babchuk <Volodymyr_Babchuk@...m.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Cc:     "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Oleksii Moisieiev <Oleksii_Moisieiev@...m.com>
Subject: Re: [PATCH] xen/pvcalls-back: fix permanently masked event channel

On 19.01.23 22:11, Volodymyr Babchuk wrote:
> There is a sequence of events that can lead to a permanently masked
> event channel, because xen_irq_lateeoi() is newer called. This happens
> when a backend receives spurious write event from a frontend. In this
> case pvcalls_conn_back_write() returns early and it does not clears the
> map->write counter. As map->write > 0, pvcalls_back_ioworker() returns
> without calling xen_irq_lateeoi(). This leaves the event channel in
> masked state, a backend does not receive any new events from a
> frontend and the whole communication stops.
> 
> Move atomic_set(&map->write, 0) to the very beginning of
> pvcalls_conn_back_write() to fix this issue.
> 
> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@...m.com>
> Reported-by: Oleksii Moisieiev <oleksii_moisieiev@...m.com>

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen


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