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Re: [PATCH 1/2] Bluetooth: Fix L2CAP ERTM packet queue corruption |
Manoj - On Wed, 25 Apr 2012, Andrei Emeltchenko wrote:
Hi Manoj, On Wed, Apr 25, 2012 at 01:59:03PM +0530, Manoj wrote:While running in L2CAP ERTM mode, sometimes ERTM packet queue gets corrupted because though method l2cap_ertm_send() is not thread-safe, it is called simultaneously from multiple threads.Could you give examples how queue is corrupted? Best regards Andrei Emeltchenko
Around the time that bluetooth-next made the switch to workqueues, I saw some issues where the packet sent in l2cap_ertm_send could be acked in tasklet context before l2cap_ertm_send finished running. This would cause the packet to be removed from the tx_q before skb_queue_is_last() was called, which would in turn result in a corrupt tx_send_head pointer.
With workqueues and proper locking, this should not be a problem. The lock that needs to be held when changing tx_q is acquired using l2cap_chan_lock(), *not* the mutex_lock() used in this patch. Callers of l2cap_ertm_send() should already hold l2cap_chan_lock(), which will provide thread safety. It looks like l2cap_chan_lock() is not held when l2cap_ertm_send() is called by l2cap_chan_send().
(Also keep in mind that l2cap_chan_lock() cannot be held when l2cap_create_iframe_pdu() is called, because it's possible to block while allocating iframe skbs)
Signed-off-by: Manoj <manojkr.sharma@xxxxxxxxxxxxxx> --- net/bluetooth/l2cap_core.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-) diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index 19807c9..a9319e2 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -1713,6 +1713,7 @@ static int l2cap_ertm_send(struct l2cap_chan *chan) if (chan->state != BT_CONNECTED) return -ENOTCONN; + mutex_lock(&chan->conn->chan_lock); while ((skb = chan->tx_send_head) && (!l2cap_tx_window_full(chan))) { if (chan->remote_max_tx && @@ -1765,7 +1766,7 @@ static int l2cap_ertm_send(struct l2cap_chan *chan) else chan->tx_send_head = skb_queue_next(&chan->tx_q, skb); } - + mutex_unlock(&chan->conn->chan_lock); return nsent; } -- 1.6.6.1
Regards, -- Mat Martineau Employee of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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