From 4c8411f8c115def968820a4df6658ccfd55d7f1a Mon Sep 17 00:00:00 2001 From: Arjan van de Ven Date: Thu, 29 May 2008 01:32:47 -0700 Subject: bluetooth: fix locking bug in the rfcomm socket cleanup handling in net/bluetooth/rfcomm/sock.c, rfcomm_sk_state_change() does the following operation: if (parent && sock_flag(sk, SOCK_ZAPPED)) { /* We have to drop DLC lock here, otherwise * rfcomm_sock_destruct() will dead lock. */ rfcomm_dlc_unlock(d); rfcomm_sock_kill(sk); rfcomm_dlc_lock(d); } } which is fine, since rfcomm_sock_kill() will call sk_free() which will call rfcomm_sock_destruct() which takes the rfcomm_dlc_lock()... so far so good. HOWEVER, this assumes that the rfcomm_sk_state_change() function always gets called with the rfcomm_dlc_lock() taken. This is the case for all but one case, and in that case where we don't have the lock, we do a double unlock followed by an attempt to take the lock, which due to underflow isn't going anywhere fast. This patch fixes this by moving the stragling case inside the lock, like the other usages of the same call are doing in this code. This was found with the help of the www.kerneloops.org project, where this deadlock was observed 51 times at this point in time: http://www.kerneloops.org/search.php?search=rfcomm_sock_destruct Signed-off-by: Arjan van de Ven Acked-by: Marcel Holtmann Signed-off-by: David S. Miller --- net/bluetooth/rfcomm/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'net/bluetooth') diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c index eb62558e9b09..0c2c93735e93 100644 --- a/net/bluetooth/rfcomm/core.c +++ b/net/bluetooth/rfcomm/core.c @@ -423,8 +423,8 @@ static int __rfcomm_dlc_close(struct rfcomm_dlc *d, int err) rfcomm_dlc_lock(d); d->state = BT_CLOSED; - rfcomm_dlc_unlock(d); d->state_change(d, err); + rfcomm_dlc_unlock(d); skb_queue_purge(&d->tx_queue); rfcomm_dlc_unlink(d); -- cgit v1.2.3 From 537d59af73d894750cff14f90fe2b6d77fbab15b Mon Sep 17 00:00:00 2001 From: Dave Young Date: Sun, 1 Jun 2008 23:50:52 -0700 Subject: bluetooth: rfcomm_dev_state_change deadlock fix There's logic in __rfcomm_dlc_close: rfcomm_dlc_lock(d); d->state = BT_CLOSED; d->state_changed(d, err); rfcomm_dlc_unlock(d); In rfcomm_dev_state_change, it's possible that rfcomm_dev_put try to take the dlc lock, then we will deadlock. Here fixed it by unlock dlc before rfcomm_dev_get in rfcomm_dev_state_change. why not unlock just before rfcomm_dev_put? it's because there's another problem. rfcomm_dev_get/rfcomm_dev_del will take rfcomm_dev_lock, but in rfcomm_dev_add the lock order is : rfcomm_dev_lock --> dlc lock so I unlock dlc before the taken of rfcomm_dev_lock. Actually it's a regression caused by commit 1905f6c736cb618e07eca0c96e60e3c024023428 ("bluetooth : __rfcomm_dlc_close lock fix"), the dlc state_change could be two callbacks : rfcomm_sk_state_change and rfcomm_dev_state_change. I missed the rfcomm_sk_state_change that time. Thanks Arjan van de Ven for the effort in commit 4c8411f8c115def968820a4df6658ccfd55d7f1a ("bluetooth: fix locking bug in the rfcomm socket cleanup handling") but he missed the rfcomm_dev_state_change lock issue. Signed-off-by: Dave Young Acked-by: Marcel Holtmann Signed-off-by: David S. Miller --- net/bluetooth/rfcomm/tty.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) (limited to 'net/bluetooth') diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c index c3f749abb2d0..c9191871c1e0 100644 --- a/net/bluetooth/rfcomm/tty.c +++ b/net/bluetooth/rfcomm/tty.c @@ -566,11 +566,22 @@ static void rfcomm_dev_state_change(struct rfcomm_dlc *dlc, int err) if (dlc->state == BT_CLOSED) { if (!dev->tty) { if (test_bit(RFCOMM_RELEASE_ONHUP, &dev->flags)) { - if (rfcomm_dev_get(dev->id) == NULL) + /* Drop DLC lock here to avoid deadlock + * 1. rfcomm_dev_get will take rfcomm_dev_lock + * but in rfcomm_dev_add there's lock order: + * rfcomm_dev_lock -> dlc lock + * 2. rfcomm_dev_put will deadlock if it's + * the last reference + */ + rfcomm_dlc_unlock(dlc); + if (rfcomm_dev_get(dev->id) == NULL) { + rfcomm_dlc_lock(dlc); return; + } rfcomm_dev_del(dev); rfcomm_dev_put(dev); + rfcomm_dlc_lock(dlc); } } else tty_hangup(dev->tty); -- cgit v1.2.3