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authorStefan Richter <stefanr@s5r6.in-berlin.de>2010-06-20 22:52:27 +0200
committerStefan Richter <stefanr@s5r6.in-berlin.de>2010-06-20 23:11:56 +0200
commit0244f57302f7e8bebd2f1ab58767eac2e9f678a6 (patch)
treeb9ea719d24b41f9df661e8de1dab36bfc3c58b11 /drivers/firewire/core-cdev.c
parent08bd34c98d631fe85744d4c920c80f48a1d95f54 (diff)
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. <linux/firewire-cdev.h> 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 <stefanr@s5r6.in-berlin.de>
Diffstat (limited to 'drivers/firewire/core-cdev.c')
-rw-r--r--drivers/firewire/core-cdev.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/drivers/firewire/core-cdev.c b/drivers/firewire/core-cdev.c
index 8cbc2b8a8272..8f8c8eeaf046 100644
--- a/drivers/firewire/core-cdev.c
+++ b/drivers/firewire/core-cdev.c
@@ -627,6 +627,8 @@ static void release_request(struct client *client,
kfree(r->data);
else
fw_send_response(r->card, r->request, RCODE_CONFLICT_ERROR);
+
+ fw_card_put(r->card);
kfree(r);
}
@@ -641,6 +643,9 @@ static void handle_request(struct fw_card *card, struct fw_request *request,
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)
@@ -686,6 +691,8 @@ static void handle_request(struct fw_card *card, struct fw_request *request,
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,
@@ -768,6 +775,7 @@ static int ioctl_send_response(struct client *client, union ioctl_arg *arg)
}
fw_send_response(r->card, r->request, a->rcode);
out:
+ fw_card_put(r->card);
kfree(r);
return ret;

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