Return-Path: Date: Thu, 20 Mar 2014 14:01:54 -0500 From: Felipe Balbi To: Felipe Balbi CC: Peter Hurley , Marcel Holtmann , Alan Cox , Greg KH , Muralidharan Karicheri , , , Linux Kernel Mailing List , Huang Shijie Subject: Re: hci_ldsic nested locking problem Message-ID: <20140320190154.GF3959@saruman.home> Reply-To: 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> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="FeAIMMcddNRN4P4/" In-Reply-To: <20140320182528.GE3959@saruman.home> List-ID: --FeAIMMcddNRN4P4/ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Mar 20, 2014 at 01:25:28PM -0500, 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 a= lready > > >>>>>taken. hci_ldisc.c's implementation of ->write_wakeup() calls > > >>>>>tty->ops->write() to actually send the characters, but that call w= ill > > >>>>>try to acquire the same port lock again. > > >>>>> > > >>>>>Looking at other line disciplines that looks like a bug in hci_ldi= sc.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 oth= er > > >colleagues who've got a platform to reproduce the problem: > >=20 > > Where's the cancel_work_sync() on teardown? >=20 > here, as a patch too this time: >=20 > 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 >=20 > LDISCs shouldn't call tty->ops->write() from within > ->write_wakeup(). >=20 > ->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. >=20 > Signed-off-by: Felipe Balbi > --- > drivers/bluetooth/hci_ldisc.c | 20 +++++++++++++++----- > drivers/bluetooth/hci_uart.h | 1 + > 2 files changed, 16 insertions(+), 5 deletions(-) >=20 > 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(struc= t hci_uart *hu) > =20 > int hci_uart_tx_wakeup(struct hci_uart *hu) > { > - struct tty_struct *tty =3D hu->tty; > - struct hci_dev *hdev =3D 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) > =20 > BT_DBG(""); > =20 > + schedule_work(&hu->write_work); > + > + return 0; > +} > + > +static void hci_uart_write_work(struct work_struct *work) > +{ > + struct hci_uart *hu =3D container_of(work, struct hci_uart, init_ready); > + struct tty_struct *tty =3D hu->tty; > + struct hci_dev *hdev =3D hu->hdev; > + struct sk_buff *skb; > + > restart: > clear_bit(HCI_UART_TX_WAKEUP, &hu->tx_state); > =20 > @@ -153,7 +161,6 @@ restart: > goto restart; > =20 > clear_bit(HCI_UART_SENDING, &hu->tx_state); > - return 0; > } > =20 > 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 =3D 65536; > =20 > INIT_WORK(&hu->init_ready, hci_uart_init_work); > + INIT_WORK(&hu->write_work, hci_uart_write_work); > =20 > spin_lock_init(&hu->rx_lock); > =20 > @@ -318,6 +326,8 @@ static void hci_uart_tty_close(struct tty_struct *tty) > if (hdev) > hci_uart_close(hdev); > =20 > + cancel_work_sync(&hy->write_work); forgot to commit, darn it --=20 balbi --FeAIMMcddNRN4P4/ Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJTKzsiAAoJEIaOsuA1yqREG7gP/0MBDdvlMWgEUAEAB1/bgcwq FnGpt/EeoiHBg8QpZtUgpQzeWW5hvJhcYoHQDPQQX6ch8+sA5h4Kp2V8Ol4643EV 5umj3/6QdFrXGAfr7ibRLTRJgUe4F6wIxO2eDFB5xhob/1HQv005rYusRPlqZ4rG ITI1lKuqAlJSmM8KzS4ZXGCKhEWGiPoK7852d4uioziGm7pXA8Kmd1LPAAWC6Z1o 1th5BSF0qvlVGSxRTTDgenBI3GqNcVvlzCZK0gjsfSitPNHPckz97iA74zNX5UsL otrQ32Vr125B8oZWhZIVUXcr6ALUFWdyLsV89AvsALVrZCqheICXlsiuOvuUFkqa V4Zyj7he7ZathUhq7qyJAWHKXLJUG9ZkhCW6Ya1Y1kUUCPfRQy7XwPQMLwfLp8at Ay6CDnfNMSk9qVJYaegeqOUZ+3W7hPwXa3rV8L47mrSWbYrrio34BLM1rJ7xqbRr FCz6/Gwf/8+5VYINlO5eHKfyyFXDm+9IRGBc+eVoSOEFyj9CfNoDHlh0O6L5XyPl E0YEk3lBQj7L9lQWaT/pmgz8HY+NYGqN0xcPs8qiI+Z7T7Kyaz9b65jntmN5Rsmj tmJ/wkIlHbVlQj/mi00azFAywPJyEjTVKE7ngS3P5Yuyadc5fcjiXe6auYuQlPl0 5kqnuK+39sZtXi68L7yC =cIOD -----END PGP SIGNATURE----- --FeAIMMcddNRN4P4/--