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

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Date:   Tue, 28 Mar 2023 12:58:38 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Oleksandr Tyshchenko <olekstysh@...il.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 12:34, Oleksandr Tyshchenko wrote:
> 
> 
> 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?

Thanks for catching!


Juergen


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