linux-kernel - Re: [PATCH 1/2] xen/evtchn: avoid WARN() when unbinding an event channel

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Date: Sun, 17 Mar 2024 15:45:07 +0000
From: Oleksandr Tyshchenko <Oleksandr_Tyshchenko@...m.com>
To: Juergen Gross <jgross@...e.com>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: Stefano Stabellini <sstabellini@...nel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        Demi Marie
 Obenour <demi@...isiblethingslab.com>
Subject: Re: [PATCH 1/2] xen/evtchn: avoid WARN() when unbinding an event
 channel



On 13.03.24 09:14, Juergen Gross wrote:

Hello Juergen


> When unbinding a user event channel, the related handler might be
> called a last time in case the kernel was built with
> CONFIG_DEBUG_SHIRQ. This might cause a WARN() in the handler.
> 
> Avoid that by adding an "unbinding" flag to struct user_event which
> will short circuit the handler.
> 
> Fixes: 9e90e58c11b7 ("xen: evtchn: Allow shared registration of IRQ handers")
> Reported-by: Demi Marie Obenour <demi@...isiblethingslab.com>
> Tested-by: Demi Marie Obenour <demi@...isiblethingslab.com>
> Signed-off-by: Juergen Gross <jgross@...e.com>


Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>


> ---
>   drivers/xen/evtchn.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c
> index 59717628ca42..f6a2216c2c87 100644
> --- a/drivers/xen/evtchn.c
> +++ b/drivers/xen/evtchn.c
> @@ -85,6 +85,7 @@ struct user_evtchn {
>   	struct per_user_data *user;
>   	evtchn_port_t port;
>   	bool enabled;
> +	bool unbinding;
>   };
>   
>   static void evtchn_free_ring(evtchn_port_t *ring)
> @@ -164,6 +165,10 @@ static irqreturn_t evtchn_interrupt(int irq, void *data)
>   	struct per_user_data *u = evtchn->user;
>   	unsigned int prod, cons;
>   
> +	/* Handler might be called when tearing down the IRQ. */
> +	if (evtchn->unbinding)
> +		return IRQ_HANDLED;
> +
>   	WARN(!evtchn->enabled,
>   	     "Interrupt for port %u, but apparently not enabled; per-user %p\n",
>   	     evtchn->port, u);
> @@ -421,6 +426,7 @@ static void evtchn_unbind_from_user(struct per_user_data *u,
>   
>   	BUG_ON(irq < 0);
>   
> +	evtchn->unbinding = true;
>   	unbind_from_irqhandler(irq, evtchn);
>   
>   	del_evtchn(u, evtchn);