From: Ronald Tschalär ronald@innovation.ch
commit 67d2f8781b9f00d1089aafcfa3dc09fcd0f343e2 upstream.
Commit dec2c92880cc5435381d50e3045ef018a762a917 ("Bluetooth: hci_ldisc: Use rwlocking to avoid closing proto races") introduced locks in hci_ldisc that are held while calling the proto functions. These locks are rwlock's, and hence do not allow sleeping while they are held. However, the proto functions that hci_bcm registers use mutexes and hence need to be able to sleep.
In more detail: hci_uart_tty_receive() and hci_uart_dequeue() both acquire the rwlock, after which they call proto->recv() and proto->dequeue(), respectively. In the case of hci_bcm these point to bcm_recv() and bcm_dequeue(). The latter both acquire the bcm_device_lock, which is a mutex, so doing so results in a call to might_sleep(). But since we're holding a rwlock in hci_ldisc, that results in the following BUG (this for the dequeue case - a similar one for the receive case is omitted for brevity):
BUG: sleeping function called from invalid context at kernel/locking/mutex.c in_atomic(): 1, irqs_disabled(): 0, pid: 7303, name: kworker/7:3 INFO: lockdep is turned off. CPU: 7 PID: 7303 Comm: kworker/7:3 Tainted: G W OE 4.13.2+ #17 Hardware name: Apple Inc. MacBookPro13,3/Mac-A5C67F76ED83108C, BIOS MBP133.8 Workqueue: events hci_uart_write_work [hci_uart] Call Trace: dump_stack+0x8e/0xd6 ___might_sleep+0x164/0x250 __might_sleep+0x4a/0x80 __mutex_lock+0x59/0xa00 ? lock_acquire+0xa3/0x1f0 ? lock_acquire+0xa3/0x1f0 ? hci_uart_write_work+0xd3/0x160 [hci_uart] mutex_lock_nested+0x1b/0x20 ? mutex_lock_nested+0x1b/0x20 bcm_dequeue+0x21/0xc0 [hci_uart] hci_uart_write_work+0xe6/0x160 [hci_uart] process_one_work+0x253/0x6a0 worker_thread+0x4d/0x3b0 kthread+0x133/0x150
We can't replace the mutex in hci_bcm, because there are other calls there that might sleep. Therefore this replaces the rwlock's in hci_ldisc with rw_semaphore's (which allow sleeping). This is a safer approach anyway as it reduces the restrictions on the proto callbacks. Also, because acquiring write-lock is very rare compared to acquiring the read-lock, the percpu variant of rw_semaphore is used.
Lastly, because hci_uart_tx_wakeup() may be called from an IRQ context, we can't block (sleep) while trying acquire the read lock there, so we use the trylock variant.
Signed-off-by: Ronald Tschalär ronald@innovation.ch Reviewed-by: Lukas Wunner lukas@wunner.de Signed-off-by: Marcel Holtmann marcel@holtmann.org Signed-off-by: Amit Pundir amit.pundir@linaro.org --- Not applicable for 4.9.y, 4.4.y and 3.18.y
drivers/bluetooth/hci_ldisc.c | 38 ++++++++++++++++++++++---------------- drivers/bluetooth/hci_uart.h | 2 +- 2 files changed, 23 insertions(+), 17 deletions(-)
diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c index 6aef3bde10d7..c823914b3a80 100644 --- a/drivers/bluetooth/hci_ldisc.c +++ b/drivers/bluetooth/hci_ldisc.c @@ -115,12 +115,12 @@ static inline struct sk_buff *hci_uart_dequeue(struct hci_uart *hu) struct sk_buff *skb = hu->tx_skb;
if (!skb) { - read_lock(&hu->proto_lock); + percpu_down_read(&hu->proto_lock);
if (test_bit(HCI_UART_PROTO_READY, &hu->flags)) skb = hu->proto->dequeue(hu);
- read_unlock(&hu->proto_lock); + percpu_up_read(&hu->proto_lock); } else { hu->tx_skb = NULL; } @@ -130,7 +130,14 @@ static inline struct sk_buff *hci_uart_dequeue(struct hci_uart *hu)
int hci_uart_tx_wakeup(struct hci_uart *hu) { - read_lock(&hu->proto_lock); + /* This may be called in an IRQ context, so we can't sleep. Therefore + * we try to acquire the lock only, and if that fails we assume the + * tty is being closed because that is the only time the write lock is + * acquired. If, however, at some point in the future the write lock + * is also acquired in other situations, then this must be revisited. + */ + if (!percpu_down_read_trylock(&hu->proto_lock)) + return 0;
if (!test_bit(HCI_UART_PROTO_READY, &hu->flags)) goto no_schedule; @@ -145,7 +152,7 @@ int hci_uart_tx_wakeup(struct hci_uart *hu) schedule_work(&hu->write_work);
no_schedule: - read_unlock(&hu->proto_lock); + percpu_up_read(&hu->proto_lock);
return 0; } @@ -247,12 +254,12 @@ static int hci_uart_flush(struct hci_dev *hdev) tty_ldisc_flush(tty); tty_driver_flush_buffer(tty);
- read_lock(&hu->proto_lock); + percpu_down_read(&hu->proto_lock);
if (test_bit(HCI_UART_PROTO_READY, &hu->flags)) hu->proto->flush(hu);
- read_unlock(&hu->proto_lock); + percpu_up_read(&hu->proto_lock);
return 0; } @@ -275,15 +282,15 @@ static int hci_uart_send_frame(struct hci_dev *hdev, struct sk_buff *skb) BT_DBG("%s: type %d len %d", hdev->name, hci_skb_pkt_type(skb), skb->len);
- read_lock(&hu->proto_lock); + percpu_down_read(&hu->proto_lock);
if (!test_bit(HCI_UART_PROTO_READY, &hu->flags)) { - read_unlock(&hu->proto_lock); + percpu_up_read(&hu->proto_lock); return -EUNATCH; }
hu->proto->enqueue(hu, skb); - read_unlock(&hu->proto_lock); + percpu_up_read(&hu->proto_lock);
hci_uart_tx_wakeup(hu);
@@ -486,7 +493,7 @@ static int hci_uart_tty_open(struct tty_struct *tty) INIT_WORK(&hu->init_ready, hci_uart_init_work); INIT_WORK(&hu->write_work, hci_uart_write_work);
- rwlock_init(&hu->proto_lock); + percpu_init_rwsem(&hu->proto_lock);
/* Flush any pending characters in the driver */ tty_driver_flush_buffer(tty); @@ -503,7 +510,6 @@ static void hci_uart_tty_close(struct tty_struct *tty) { struct hci_uart *hu = tty->disc_data; struct hci_dev *hdev; - unsigned long flags;
BT_DBG("tty %p", tty);
@@ -518,9 +524,9 @@ static void hci_uart_tty_close(struct tty_struct *tty) hci_uart_close(hdev);
if (test_bit(HCI_UART_PROTO_READY, &hu->flags)) { - write_lock_irqsave(&hu->proto_lock, flags); + percpu_down_write(&hu->proto_lock); clear_bit(HCI_UART_PROTO_READY, &hu->flags); - write_unlock_irqrestore(&hu->proto_lock, flags); + percpu_up_write(&hu->proto_lock);
cancel_work_sync(&hu->write_work);
@@ -582,10 +588,10 @@ static void hci_uart_tty_receive(struct tty_struct *tty, const u8 *data, if (!hu || tty != hu->tty) return;
- read_lock(&hu->proto_lock); + percpu_down_read(&hu->proto_lock);
if (!test_bit(HCI_UART_PROTO_READY, &hu->flags)) { - read_unlock(&hu->proto_lock); + percpu_up_read(&hu->proto_lock); return; }
@@ -593,7 +599,7 @@ static void hci_uart_tty_receive(struct tty_struct *tty, const u8 *data, * tty caller */ hu->proto->recv(hu, data, count); - read_unlock(&hu->proto_lock); + percpu_up_read(&hu->proto_lock);
if (hu->hdev) hu->hdev->stat.byte_rx += count; diff --git a/drivers/bluetooth/hci_uart.h b/drivers/bluetooth/hci_uart.h index d9cd95d81149..66e8c68e4607 100644 --- a/drivers/bluetooth/hci_uart.h +++ b/drivers/bluetooth/hci_uart.h @@ -87,7 +87,7 @@ struct hci_uart { struct work_struct write_work;
const struct hci_uart_proto *proto; - rwlock_t proto_lock; /* Stop work for proto close */ + struct percpu_rw_semaphore proto_lock; /* Stop work for proto close */ void *priv;
struct sk_buff *tx_skb;