From mboxrd@z Thu Jan 1 00:00:00 1970 From: Huang Shijie Subject: Re: [PATCH RFC] tty_ldisc: add more limits to the @write_wakeup Date: Fri, 6 Dec 2013 18:34:51 +0800 Message-ID: <52A1A84B.80409@freescale.com> References: <1384327803-5925-1-git-send-email-b32955@freescale.com> Mime-Version: 1.0 Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mail-db9lp0253.outbound.messaging.microsoft.com ([213.199.154.253]:51501 "EHLO db9outboundpool.messaging.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754481Ab3LFKcY convert rfc822-to-8bit (ORCPT ); Fri, 6 Dec 2013 05:32:24 -0500 In-Reply-To: <1384327803-5925-1-git-send-email-b32955@freescale.com> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Huang Shijie Cc: gregkh@linuxfoundation.org, linux-serial@vger.kernel.org, marcel@holtmann.org, linux-bluetooth@vger.kernel.org =D3=DA 2013=C4=EA11=D4=C213=C8=D5 15:30, Huang Shijie =D0=B4=B5=C0: > In the uart_handle_cts_change(), uart_write_wakeup() is called after > we call @uart_port->ops->start_tx(). > > The Documentation/serial/driver tells us: > ----------------------------------------------- > start_tx(port) > Start transmitting characters. > > Locking: port->lock taken. > Interrupts: locally disabled. > ----------------------------------------------- > > So when the uart_write_wakeup() is called, the port->lock is taken by > the upper. See the following callstack: > > |_ uart_write_wakeup > |_ tty_wakeup > |_ ld->ops->write_wakeup > > With the port->lock held, we call the @write_wakeup. Some implemetati= on of > the @write_wakeup does not notice that the port->lock is held, and it= still > tries to send data with uart_write() which will try to grab the prot-= >lock. > A dead lock occurs, see the following log caught in the Bluetooth by = uart: > > -------------------------------------------------------------------- > BUG: spinlock lockup suspected on CPU#0, swapper/0/0 > lock: 0xdc3f4410, .magic: dead4ead, .owner: swapper/0/0, .owner_cpu:= 0 > CPU: 0 PID: 0 Comm: swapper/0 Tainted: G W 3.10.17-16839-ge= 4a1bef #1320 > [<80014cbc>] (unwind_backtrace+0x0/0x138) from [<8001251c>] (show_sta= ck+0x10/0x14) > [<8001251c>] (show_stack+0x10/0x14) from [<802816ac>] (do_raw_spin_lo= ck+0x108/0x184) > [<802816ac>] (do_raw_spin_lock+0x108/0x184) from [<806a22b0>] (_raw_s= pin_lock_irqsave+0x54/0x60) > [<806a22b0>] (_raw_spin_lock_irqsave+0x54/0x60) from [<802f5754>] (ua= rt_write+0x38/0xe0) > [<802f5754>] (uart_write+0x38/0xe0) from [<80455270>] (hci_uart_tx_wa= keup+0xa4/0x168) > [<80455270>] (hci_uart_tx_wakeup+0xa4/0x168) from [<802dab18>] (tty_w= akeup+0x50/0x5c) > [<802dab18>] (tty_wakeup+0x50/0x5c) from [<802f81a4>] (imx_rtsint+0x5= 0/0x80) > [<802f81a4>] (imx_rtsint+0x50/0x80) from [<802f88f4>] (imx_int+0x158/= 0x17c) > [<802f88f4>] (imx_int+0x158/0x17c) from [<8007abe0>] (handle_irq_even= t_percpu+0x50/0x194) > [<8007abe0>] (handle_irq_event_percpu+0x50/0x194) from [<8007ad60>] (= handle_irq_event+0x3c/0x5c) > -------------------------------------------------------------------- > > This patch adds more limits to the @write_wakeup, the one who wants t= o > implemet the @write_wakeup should follow the limits which avoid the d= eadlock. > > Signed-off-by: Huang Shijie > --- > include/linux/tty_ldisc.h | 5 ++++- > 1 files changed, 4 insertions(+), 1 deletions(-) > > diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h > index f15c898..539ccc5 100644 > --- a/include/linux/tty_ldisc.h > +++ b/include/linux/tty_ldisc.h > @@ -91,7 +91,10 @@ > * This function is called by the low-level tty driver to signal > * that line discpline should try to send more characters to the > * low-level driver for transmission. If the line discpline does > - * not have any more data to send, it can just return. > + * not have any more data to send, it can just return. If the line > + * discipline does have some data to send, please arise a tasklet > + * or workqueue to do the real data transfer. Do not send data in > + * this hook, it may leads to a deadlock. > * > * int (*hangup)(struct tty_struct *) > * just a ping. In actually, this is a BUG in the tty code or BT code. thanks Huang Shijie -- To unsubscribe from this list: send the line "unsubscribe linux-serial"= in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html