linux-kernel - Re: [PATCH] xen/pvcalls: don't call bind_evtchn_to

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Date:   Tue, 28 Mar 2023 13:34:19 +0300
From:   Oleksandr Tyshchenko <olekstysh@...il.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        xen-devel@...ts.xenproject.org, Dan Carpenter <error27@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen/pvcalls: don't call bind_evtchn_to_irqhandler() under
 lock



On 28.03.23 12:39, Juergen Gross wrote:

Hello Juergen


> bind_evtchn_to_irqhandler() shouldn't be called under spinlock, as it
> can sleep.
> 
> This requires to move the calls of create_active() out of the locked
> regions. This is no problem, as the worst which could happen would be
> a spurious call of the interrupt handler, causing a spurious wake_up().
> 
> Reported-by: Dan Carpenter <error27@...il.com>
> Link: https://lore.kernel.org/lkml/Y+JUIl64UDmdkboh@kadam/
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>   drivers/xen/pvcalls-front.c | 46 ++++++++++++++++++++++---------------
>   1 file changed, 27 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> index d5d589bda243..6e5d712e3115 100644
> --- a/drivers/xen/pvcalls-front.c
> +++ b/drivers/xen/pvcalls-front.c
> @@ -227,22 +227,31 @@ static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id)
>   
>   static void free_active_ring(struct sock_mapping *map);
>   
> -static void pvcalls_front_free_map(struct pvcalls_bedata *bedata,
> -				   struct sock_mapping *map)
> +static void pvcalls_front_destroy_active(struct pvcalls_bedata *bedata,
> +					 struct sock_mapping *map)
>   {
>   	int i;
>   
>   	unbind_from_irqhandler(map->active.irq, map);
>   
> -	spin_lock(&bedata->socket_lock);
> -	if (!list_empty(&map->list))
> -		list_del_init(&map->list);
> -	spin_unlock(&bedata->socket_lock);
> +	if (bedata) {
> +		spin_lock(&bedata->socket_lock);
> +		if (!list_empty(&map->list))
> +			list_del_init(&map->list);
> +		spin_unlock(&bedata->socket_lock);
> +	}
>   
>   	for (i = 0; i < (1 << PVCALLS_RING_ORDER); i++)
>   		gnttab_end_foreign_access(map->active.ring->ref[i], NULL);
>   	gnttab_end_foreign_access(map->active.ref, NULL);
> +
>   	free_active_ring(map);
> +}
> +
> +static void pvcalls_front_free_map(struct pvcalls_bedata *bedata,
> +				   struct sock_mapping *map)
> +{
> +	pvcalls_front_destroy_active(bedata, map);
>   
>   	kfree(map);
>   }
> @@ -433,19 +442,18 @@ int pvcalls_front_connect(struct socket *sock, struct sockaddr *addr,
>   		pvcalls_exit_sock(sock);
>   		return ret;
>   	}
> -
> -	spin_lock(&bedata->socket_lock);
> -	ret = get_request(bedata, &req_id);
> +	ret = create_active(map, &evtchn);
>   	if (ret < 0) {
> -		spin_unlock(&bedata->socket_lock);
>   		free_active_ring(map);
>   		pvcalls_exit_sock(sock);
>   		return ret;
>   	}
> -	ret = create_active(map, &evtchn);
> +
> +	spin_lock(&bedata->socket_lock);
> +	ret = get_request(bedata, &req_id);
>   	if (ret < 0) {
>   		spin_unlock(&bedata->socket_lock);
> -		free_active_ring(map);
> +		pvcalls_front_destroy_active(NULL, map);
>   		pvcalls_exit_sock(sock);
>   		return ret;
>   	}
> @@ -821,28 +829,28 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
>   		pvcalls_exit_sock(sock);
>   		return ret;
>   	}
> -	spin_lock(&bedata->socket_lock);
> -	ret = get_request(bedata, &req_id);
> +	ret = create_active(map2, &evtchn);
>   	if (ret < 0) {
> +		free_active_ring(map2);
> +		kfree(map2);
>   		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
>   			  (void *)&map->passive.flags);
>   		spin_unlock(&bedata->socket_lock);


Looks like we also need to remove spin_unlock() above, correct?


> -		free_active_ring(map2);
> -		kfree(map2);
>   		pvcalls_exit_sock(sock);
>   		return ret;
>   	}
>   
> -	ret = create_active(map2, &evtchn);
> +	spin_lock(&bedata->socket_lock);
> +	ret = get_request(bedata, &req_id);
>   	if (ret < 0) {
> -		free_active_ring(map2);
> -		kfree(map2);
>   		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
>   			  (void *)&map->passive.flags);
>   		spin_unlock(&bedata->socket_lock);
> +		pvcalls_front_free_map(bedata, map2);
>   		pvcalls_exit_sock(sock);
>   		return ret;
>   	}
> +
>   	list_add_tail(&map2->list, &bedata->socket_mappings);
>   
>   	req = RING_GET_REQUEST(&bedata->ring, req_id);