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author | Stefan Richter <stefanr@s5r6.in-berlin.de> | 2010-06-20 22:52:27 +0200 |
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committer | Stefan Richter <stefanr@s5r6.in-berlin.de> | 2010-06-20 23:11:56 +0200 |
commit | 0244f57302f7e8bebd2f1ab58767eac2e9f678a6 (patch) | |
tree | b9ea719d24b41f9df661e8de1dab36bfc3c58b11 /drivers/firewire | |
parent | firewire: cdev: fix responses to nodes at different card (diff) | |
download | linux-0244f57302f7e8bebd2f1ab58767eac2e9f678a6.tar.xz linux-0244f57302f7e8bebd2f1ab58767eac2e9f678a6.zip |
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')
-rw-r--r-- | drivers/firewire/core-cdev.c | 8 |
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; |