Return-Path: Date: Thu, 20 Mar 2014 14:25:33 -0500 From: Felipe Balbi To: Peter Hurley CC: , Marcel Holtmann , Alan Cox , Greg KH , Muralidharan Karicheri , , , Linux Kernel Mailing List , Huang Shijie Subject: Re: hci_ldsic nested locking problem Message-ID: <20140320192533.GK3959@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> <532B3E93.7060902@hurleysoftware.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="IuJpT0rwbUevm2bB" In-Reply-To: <532B3E93.7060902@hurleysoftware.com> List-ID: --IuJpT0rwbUevm2bB Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi, On Thu, Mar 20, 2014 at 03:16:35PM -0400, Peter Hurley wrote: > 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 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: > >> > >>Where's the cancel_work_sync() on teardown? > > > >here, as a patch too this time: >=20 > Thanks. Minor edits below but, strictly speaking, not necessary. >=20 > Reviewed-by: Peter Hurley >=20 >=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 > > > >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. > > >=20 > I know you found it independently but ? >=20 > Reported-by: Huang Shijie I will never add any *-by tags without seeing it in the mailing list. Now I can add it to the patch and send it as a real patch (git send-email it). > >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= =2Ec > >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(stru= ct hci_uart *hu) > > > > 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) > > > > BT_DBG(""); > > > >+ 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; > >+ >=20 > + /* FIXME: if bad skb length or tty->ops->write() returns < 0 ??? */ >=20 > > 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 =3D 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 *tt= y) > > 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; > > >=20 --=20 balbi --IuJpT0rwbUevm2bB Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJTK0CtAAoJEIaOsuA1yqRESTcQALFnk4AN9xnWTgDUn2oRcM9n CfJlNRpjcLjbv1YgrYY6wE0Cmib/QWtm5LJbOp12LvlWyq9YfQA11bIrBs4ef0Ox ESI5IcNNJwvhd/BoiaRm/wb7S2ql6fU+MxQOPh8wM4U20XLK1LOcUduaaNPrCkyu 6DbiaGaRulNt/Utknu91upsdnQ+zhALQw2Lz2fM3ab6Poh16kcMjWUexe9v/jXIc UwPHPje0QugrKoe8xs2FKAmtEZsKstzggvVfTAsFgRJ2nFWoh/jT6/2Q+wZ+Zkv8 0f/gl11VYjUmEyo6kG6z93wgj/A7MmLETZnkDDekIHKkSgADMjyRsHme17E9TUcv pGPoW90Yxz9/5RZSTIUKHRDoAg3+FY1f4JFvXoIIeKpP/23M+ebw7EVjFwkj+fxY ndOKmq6E8AW5MxkplQ3N90ftlFQ8J8QOsnSlfiqmMzQUrQndWsz8ST37XopESa/1 sWtJRrnpr8uJYaoziWNvCy3l3yunhplfZbvjYJ6qWCjGJ6iOdspqTEtyeV/NrYla Y13kEhl8s8igF/4YT7UAInM+7Oe2MZtaJOTOoYhEOi8q0TYf8LzSMm4DeLuGFj+I QItJOvFf0usq2tZDducrN6dI/kT1QD0XAE6UxfEpCMNMw3PxRfSIK0SlQSP/hoh9 xx9zlUpDuZi7YVzqnDwt =gpFl -----END PGP SIGNATURE----- --IuJpT0rwbUevm2bB--