Return-Path: Message-ID: <532B3E93.7060902@hurleysoftware.com> Date: Thu, 20 Mar 2014 15:16:35 -0400 From: Peter Hurley MIME-Version: 1.0 To: balbi@ti.com CC: Marcel Holtmann , Alan Cox , Greg KH , Muralidharan Karicheri , linux-bluetooth@vger.kernel.org, linux-serial@vger.kernel.org, Linux Kernel Mailing List , Huang Shijie Subject: Re: hci_ldsic nested locking problem References: <20140320163435.GH32692@saruman.home> <1395333736.22077.32.camel@acox1-desk.ger.corp.intel.com> <20140320171621.GA2827@saruman.home> <532B25FC.3070408@hurleysoftware.com> <20140320181145.GC3959@saruman.home> <532B319D.4090208@hurleysoftware.com> <20140320182528.GE3959@saruman.home> In-Reply-To: <20140320182528.GE3959@saruman.home> Content-Type: text/plain; charset=UTF-8; format=flowed List-ID: On 03/20/2014 02:25 PM, Felipe Balbi wrote: > On Thu, Mar 20, 2014 at 02:21:17PM -0400, Peter Hurley wrote: >> On 03/20/2014 02:11 PM, Felipe Balbi wrote: >>> On Thu, Mar 20, 2014 at 01:31:40PM -0400, Peter Hurley wrote: >>>> [ +cc Huang Shijie ] >>>> >>>> On 03/20/2014 01:16 PM, Felipe Balbi wrote: >>>>> On Thu, Mar 20, 2014 at 04:42:16PM +0000, Alan Cox wrote: >>>>>> On Thu, 2014-03-20 at 11:34 -0500, Felipe Balbi wrote: >>>>>>> Hi, >>>>>>> >>>>>>> when 8250 driver calls uart_write_wakeup(), the tty port lock is already >>>>>>> taken. hci_ldisc.c's implementation of ->write_wakeup() calls >>>>>>> tty->ops->write() to actually send the characters, but that call will >>>>>>> try to acquire the same port lock again. >>>>>>> >>>>>>> Looking at other line disciplines that looks like a bug in hci_ldisc.c. >>>>>>> Am I correct to assume that ->write_wakeup() is supposed to *just* >>>>>>> wakeup the bottom half so we handle ->write() in another context ? >>>>>>> >>>>>>> Is it legal to call tty->ops->write() from within ->write_wakeup() ? >>>>>> >>>>>> It isn't because you might send all the bytes and go >>>>>> >>>>>> write >>>>>> write_wakeup >>>>>> write >>>>>> write wakeup >>>>>> ... >>>>>> >>>>>> and recurse >>>>> >>>>> cool, so there really is a bug in hci_ldisc. Marcel, any tips on how do >>>>> you want this to be sorted out ? >>>> >>>> hci_uart_tx_wakeup() should perform the I/O as work. >>>> FWIW, this was reported by Huang Shijie back on Dec 6. >>>> >>>> I'd fix it but I have no way to test it. >>> >>> here's a build-tested only patch which is waiting for testing from other >>> colleagues who've got a platform to reproduce the problem: >> >> Where's the cancel_work_sync() on teardown? > > here, as a patch too this time: Thanks. Minor edits below but, strictly speaking, not necessary. Reviewed-by: Peter Hurley > From 3ee6b74833f154df64a6164476b854846206a3f2 Mon Sep 17 00:00:00 2001 > From: Felipe Balbi > Date: Thu, 20 Mar 2014 13:20:10 -0500 > Subject: [PATCH] bluetooth: hci_ldisc: fix deadlock condition > > LDISCs shouldn't call tty->ops->write() from within > ->write_wakeup(). > > ->write_wakeup() is called with port lock taken and > IRQs disabled, tty->ops->write() will try to acquire > the same port lock and we will deadlock. > I know you found it independently but ? Reported-by: Huang Shijie > Signed-off-by: Felipe Balbi > --- > drivers/bluetooth/hci_ldisc.c | 20 +++++++++++++++----- > drivers/bluetooth/hci_uart.h | 1 + > 2 files changed, 16 insertions(+), 5 deletions(-) > > diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c > index 6e06f6f..ecdd765 100644 > --- a/drivers/bluetooth/hci_ldisc.c > +++ b/drivers/bluetooth/hci_ldisc.c > @@ -118,10 +118,6 @@ static inline struct sk_buff *hci_uart_dequeue(struct hci_uart *hu) > > int hci_uart_tx_wakeup(struct hci_uart *hu) > { > - struct tty_struct *tty = hu->tty; > - struct hci_dev *hdev = hu->hdev; > - struct sk_buff *skb; > - > if (test_and_set_bit(HCI_UART_SENDING, &hu->tx_state)) { > set_bit(HCI_UART_TX_WAKEUP, &hu->tx_state); > return 0; > @@ -129,6 +125,18 @@ int hci_uart_tx_wakeup(struct hci_uart *hu) > > BT_DBG(""); > > + schedule_work(&hu->write_work); > + > + return 0; > +} > + > +static void hci_uart_write_work(struct work_struct *work) > +{ > + struct hci_uart *hu = container_of(work, struct hci_uart, init_ready); > + struct tty_struct *tty = hu->tty; > + struct hci_dev *hdev = hu->hdev; > + struct sk_buff *skb; > + + /* FIXME: if bad skb length or tty->ops->write() returns < 0 ??? */ > restart: > clear_bit(HCI_UART_TX_WAKEUP, &hu->tx_state); > > @@ -153,7 +161,6 @@ restart: > goto restart; > > clear_bit(HCI_UART_SENDING, &hu->tx_state); > - return 0; > } > > static void hci_uart_init_work(struct work_struct *work) > @@ -281,6 +288,7 @@ static int hci_uart_tty_open(struct tty_struct *tty) > tty->receive_room = 65536; > > INIT_WORK(&hu->init_ready, hci_uart_init_work); > + INIT_WORK(&hu->write_work, hci_uart_write_work); > > spin_lock_init(&hu->rx_lock); > > @@ -318,6 +326,8 @@ static void hci_uart_tty_close(struct tty_struct *tty) > if (hdev) > hci_uart_close(hdev); > > + cancel_work_sync(&hy->write_work); > + > if (test_and_clear_bit(HCI_UART_PROTO_SET, &hu->flags)) { > if (hdev) { > if (test_bit(HCI_UART_REGISTERED, &hu->flags)) > diff --git a/drivers/bluetooth/hci_uart.h b/drivers/bluetooth/hci_uart.h > index fffa61f..12df101 100644 > --- a/drivers/bluetooth/hci_uart.h > +++ b/drivers/bluetooth/hci_uart.h > @@ -68,6 +68,7 @@ struct hci_uart { > unsigned long hdev_flags; > > struct work_struct init_ready; > + struct work_struct write_work; > > struct hci_uart_proto *proto; > void *priv; >