Re: [PATCH v2] xen/pvcalls: don't call bind_evtchn_to_irqhandler() under lock

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

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

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
> 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
>