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Date:	Thu, 20 Mar 2014 13:25:28 -0500
From:	Felipe Balbi <balbi@...com>
To:	Peter Hurley <peter@...leysoftware.com>
CC:	<balbi@...com>, Marcel Holtmann <marcel@...tmann.org>,
	Alan Cox <alan@...ux.intel.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Muralidharan Karicheri <m-karicheri2@...com>,
	<linux-bluetooth@...r.kernel.org>, <linux-serial@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Huang Shijie <b32955@...escale.com>
Subject: Re: hci_ldsic nested locking problem

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:

From 3ee6b74833f154df64a6164476b854846206a3f2 Mon Sep 17 00:00:00 2001
From: Felipe Balbi <balbi@...com>
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.

Signed-off-by: Felipe Balbi <balbi@...com>
---
 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;
+
 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;
-- 
1.9.1.286.g5172cb3


-- 
balbi

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