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Bluetooth: Fix write_room() calculation

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The skb truesize of a 12-byte payload with a 10-byte head/tail
reserve is 768 bytes. Consequently, even with 40 tx_credits, at
most 6 packets could be queued at any one time:

  40 tx_credits * 127-byte mtu < 768-byte truesize * 7

This error could also cause the tx queue to apparently stall if
credit flow control is disabled (where tx_credits is fixed at 5),
or if the receiver only granted a limited number of tx credits
(eg., less than 7).

Instead, track the outstanding number of queued packets not yet sent
in wmem_alloc and allow for a maximum of 40 queued packets. Report
the space avail for a single write() as the mtu * number of packets
left before reaching the maximum.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Tested-By: Alexander Holler <holler@ahsoftware.de>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
This commit is contained in:
Peter Hurley 2014-02-09 20:59:24 -05:00 committed by Marcel Holtmann
parent b16b435131
commit 8981be9b2f
1 changed files with 5 additions and 9 deletions
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14
net/bluetooth/rfcomm/tty.c
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@ -352,20 +352,16 @@ static inline unsigned int rfcomm_room(struct rfcomm_dev *dev)
{
struct rfcomm_dlc *dlc = dev->dlc;
/* The limit is bogus; the number of packets which can
* currently be sent by the krfcommd thread has no relevance
* to the number of packets which can be queued on the dlc's
* tx queue.
*/
int limit = dlc->mtu * (dlc->tx_credits?:1);
/* Limit the outstanding number of packets not yet sent to 40 */
int pending = 40 - atomic_read(&dev->wmem_alloc);
return max(0, limit - atomic_read(&dev->wmem_alloc));
return max(0, pending) * dlc->mtu;
}
static void rfcomm_wfree(struct sk_buff *skb)
{
struct rfcomm_dev *dev = (void *) skb->sk;
atomic_sub(skb->truesize, &dev->wmem_alloc);
atomic_dec(&dev->wmem_alloc);
if (test_bit(RFCOMM_TTY_ATTACHED, &dev->flags))
tty_port_tty_wakeup(&dev->port);
tty_port_put(&dev->port);
@ -374,7 +370,7 @@ static void rfcomm_wfree(struct sk_buff *skb)
static void rfcomm_set_owner_w(struct sk_buff *skb, struct rfcomm_dev *dev)
{
tty_port_get(&dev->port);
atomic_add(skb->truesize, &dev->wmem_alloc);
atomic_inc(&dev->wmem_alloc);
skb->sk = (void *) dev;
skb->destructor = rfcomm_wfree;
}