On Sat, 2023-07-08 at 14:36 +0100, Simon Horman wrote:
> On Fri, Jul 07, 2023 at 12:43:57PM +0200, Niklas Schnelle wrote:
> > The clients array references all registered clients and is protected by
> > the clients_lock. Besides its use as general list of clients the clients
> > array is accessed in ism_handle_irq() to forward ISM device events to
> > clients.
> >
> > While the clients_lock is taken in the IRQ handler when calling
> > handle_event() it is however incorrectly not held during the
> > client->handle_irq() call and for the preceding clients[] access leaving
> > it unprotected against concurrent client (un-)registration.
> >
> > Furthermore the accesses to ism->sba_client_arr[] in ism_register_dmb()
> > and ism_unregister_dmb() are not protected by any lock. This is
> > especially problematic as the client ID from the ism->sba_client_arr[]
> > is not checked against NO_CLIENT and neither is the client pointer
> > checked.
> >
> > Instead of expanding the use of the clients_lock further add a separate
> > array in struct ism_dev which references clients subscribed to the
> > device's events and IRQs. This array is protected by ism->lock which is
> > already taken in ism_handle_irq() and can be taken outside the IRQ
> > handler when adding/removing subscribers or the accessing
> > ism->sba_client_arr[]. This also means that the clients_lock is no
> > longer taken in IRQ context.
> >
> > Fixes: 89e7d2ba61b7 ("net/ism: Add new API for client registration")
> > Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
>
> ...
>
> > @@ -71,6 +80,7 @@ int ism_register_client(struct ism_client *client)
> > list_for_each_entry(ism, &ism_dev_list.list, list) {
> > ism->priv[i] = NULL;
> > client->add(ism);
> > + ism_setup_forwarding(client, ism);
> > }
> > }
> > mutex_unlock(&ism_dev_list.mutex);
>
> ...
>
> > @@ -92,6 +102,9 @@ int ism_unregister_client(struct ism_client *client)
> > max_client--;
> > spin_unlock_irqrestore(&clients_lock, flags);
> > list_for_each_entry(ism, &ism_dev_list.list, list) {
> > + spin_lock_irqsave(&ism->lock, flags);
>
> Hi Niklas,
>
> The lock is taken here.
>
> > + /* Stop forwarding IRQs and events */
> > + ism->subs[client->id] = NULL;
> > for (int i = 0; i < ISM_NR_DMBS; ++i) {
> > if (ism->sba_client_arr[i] == client->id) {
> > pr_err("%s: attempt to unregister client '%s'"
> > @@ -101,6 +114,7 @@ int ism_unregister_client(struct ism_client *client)
> > goto out;
>
> But it does not appear to be released
> (by the call to spin_unlock_irqrestore() below)
> if goto out is called here.
Good catch. Yes I screwed this up while splitting the patch up. The
spin_unlock_irqrestore() is there after patch 3 but should have been
added in patch 1. As far as I can see all 3 patches have already been
applied, otherwise I'd send a v3. Thankfully even in the in between
state this error case can really onlt happen due to driver bugs so
maybe it's okay?
>
> > }
> > }
> > + spin_unlock_irqrestore(&ism->lock, flags);
> > }
> > out:
> > mutex_unlock(&ism_dev_list.mutex);
