Date: Sun, 20 Jun 2010 22:52:27 +0200 (CEST) From: Stefan Richter Subject: firewire: cdev: count references of cards during inbound transactions If a request comes in to an address range managed by a userspace driver i.e. client, the card instance of request and response may differ from the card instance of the client device. Therefore we need to take a reference of the card until the response was sent. I thought about putting the reference counting into core-transaction.c, but the various high-level drivers besides cdev clients (firewire-net, firewire-sbp2, firedtv) use the card pointer in their fw_address_handler address_callback method only to look up devices of which they already hold the necessary references. So this seems to be a specific firewire-cdev issue which is better addressed locally. We do not need the reference - in case of FCP_REQUEST or FCP_RESPONSE requests because then the firewire-core will send the split transaction response for us already in the context of the request handler, - if it is the same card as the client device's because we hold a card reference indirectly via teh client->device reference. To keep things simple, we take the reference nevertheless. Jay Fenlason wrote: > there's no way for the core to tell cdev "this card is gone, > kill any inbound transactions on it", while cdev holds the transaction > open until userspace issues a SEND_RESPONSE ioctl, which may be a very, > very long time. But when it does, it calls fw_send_response(), which > will dereference the card... > > So how unhappy are we about userspace potentially holding a fw_card > open forever? While termination of inbound transcations at card removal could be implemented, it is IMO not worth the effort. Currently, the effect of holding a reference of a card that has been removed is to block the process that called the pci_remove of the card. This is - either a user process ran by root. Root can find and kill processes that have /dev/fw* open, if desired. - a kernel thread (which one?) in case of hot removal of a PCCard or ExpressCard. The latter case could be a problem indeed. firewire-core's card shutdown and card release should probably be improved not to block in shutdown, just to defer freeing of memory until release. This is not a new problem though; the same already always happens with the client->device->card without the need of inbound transactions or other special conditions involved, other than the client not closing the file. Signed-off-by: Stefan Richter --- drivers/firewire/core-cdev.c | 8 ++++++++ 1 file changed, 8 insertions(+) Index: b/drivers/firewire/core-cdev.c =================================================================== --- a/drivers/firewire/core-cdev.c +++ b/drivers/firewire/core-cdev.c @@ -628,6 +628,8 @@ static void release_request(struct clien kfree(r->data); else fw_send_response(r->card, r->request, RCODE_CONFLICT_ERROR); + + fw_card_put(r->card); kfree(r); } @@ -642,6 +644,9 @@ static void handle_request(struct fw_car void *fcp_frame = NULL; int ret; + /* card may be different from handler->client->device->card */ + fw_card_get(card); + r = kmalloc(sizeof(*r), GFP_ATOMIC); e = kmalloc(sizeof(*e), GFP_ATOMIC); if (r == NULL || e == NULL) @@ -687,6 +692,8 @@ static void handle_request(struct fw_car if (!is_fcp_request(request)) fw_send_response(card, request, RCODE_CONFLICT_ERROR); + + fw_card_put(card); } static void release_address_handler(struct client *client, @@ -769,6 +776,7 @@ static int ioctl_send_response(struct cl } fw_send_response(r->card, r->request, a->rcode); out: + fw_card_put(r->card); kfree(r); return ret;