Re: [PATCH] xen/pvcalls: don't call bind_evtchn_to_irqhandler() under lock

[Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>]

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@xxxxxxxxx>
> Link: https://lore.kernel.org/lkml/Y+JUIl64UDmdkboh@kadam/
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>   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);