linux-kernel - Re: [PATCH v2] xen/pvcalls: don't call bind_evtchn_to

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Date:   Fri, 7 Apr 2023 15:08:55 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Juergen Gross <jgross@...e.com>
cc:     linux-kernel@...r.kernel.org,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        xen-devel@...ts.xenproject.org, Dan Carpenter <error27@...il.com>
Subject: Re: [PATCH v2] xen/pvcalls: don't call bind_evtchn_to_irqhandler()
 under lock

On Mon, 3 Apr 2023, Juergen Gross wrote:
> 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>

Reviewed-by: Stefano Stabellini <sstabellini@...nel.org>


> ---
> V2:
> - remove stale spin_unlock() (Oleksandr Tyshchenko)
> ---
>  drivers/xen/pvcalls-front.c | 46 +++++++++++++++++++++----------------
>  1 file changed, 26 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> index d5d589bda243..b72ee9379d77 100644
> --- a/drivers/xen/pvcalls-front.c
> +++ b/drivers/xen/pvcalls-front.c
> @@ -227,22 +227,30 @@ 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 +441,18 @@ 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 +828,27 @@ 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) {
> -		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
> -			  (void *)&map->passive.flags);
> -		spin_unlock(&bedata->socket_lock);
>  		free_active_ring(map2);
>  		kfree(map2);
> +		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
> +			  (void *)&map->passive.flags);
>  		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);
> -- 
> 2.35.3
>