Re: Linux 6.7-rc1+: WARNING at drivers/xen/evtchn.c:167 evtchn_interrupt

[Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>]

On Tue, Mar 12, 2024 at 02:10:02PM +0100, Juergen Gross wrote:
> On 30.11.23 03:34, Marek Marczykowski-Górecki wrote:
> > Hi,
> > 
> > While testing 6.7-rc3 on Qubes OS I found several warning like in the
> > subject in dom0 log. I see them when running 6.7-rc1 too. I'm not sure
> > what exactly triggers the issue, but my guess would be unbinding an
> > event channel from userspace (closing vchan connection).
> > 
> > Specific message:
> > 
> > [   83.973377] ------------[ cut here ]------------
> > [   83.975523] Interrupt for port 77, but apparently not enabled; per-user 
> > 00000000a0e9f1d1
> 
> Finally I think I have a fix (thanks to Demi for finding the problematic patch
> through bisecting).
> 
> Could you please try the attached patch? It is based on current upstream, but
> I think it should apply to 6.7 or stable 6.6, too.
> 
> 
> Juergen

> From 9d673c37b2d0c9aa274c53f619c4e9e43a419f41 Mon Sep 17 00:00:00 2001
> From: Juergen Gross <jgross@xxxxxxxx>
> To: linux-kernel@xxxxxxxxxxxxxxx
> Cc: Juergen Gross <jgross@xxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Date: Tue, 12 Mar 2024 13:52:24 +0100
> Subject: [PATCH] xen/evtchn: avoid WARN() when unbinding an event channel
> 
> 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")
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>  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);
> -- 
> 2.35.3

That fixes the problem, thanks!  Code looks good to me.

Reported-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
Tested-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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