From mboxrd@z Thu Jan 1 00:00:00 1970 From: Felipe Balbi Subject: [PATCH 01/13] tty_ldisc: add more limits to the @write_wakeup Date: Wed, 23 Apr 2014 09:58:25 -0500 Message-ID: <1398265117-11793-1-git-send-email-balbi@ti.com> Mime-Version: 1.0 Content-Type: text/plain Return-path: Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Greg KH Cc: marcel-kz+m5ild9QBg9hUCZPvPmw@public.gmane.org, gustavo-THi1TnShQwVAfugRpC6u6w@public.gmane.org, johan.hedberg-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, jslaby-AlSwsSmVLrQ@public.gmane.org, grant.likely-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, Linux Kernel Mailing List , linux-bluetooth-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-serial-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Linux OMAP Mailing List , Tony Lindgren , Huang Shijie , Felipe Balbi List-Id: devicetree@vger.kernel.org From: Huang Shijie 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 implemetation 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-ge4a1bef #1320 [<80014cbc>] (unwind_backtrace+0x0/0x138) from [<8001251c>] (show_stack+0x10/0x14) [<8001251c>] (show_stack+0x10/0x14) from [<802816ac>] (do_raw_spin_lock+0x108/0x184) [<802816ac>] (do_raw_spin_lock+0x108/0x184) from [<806a22b0>] (_raw_spin_lock_irqsave+0x54/0x60) [<806a22b0>] (_raw_spin_lock_irqsave+0x54/0x60) from [<802f5754>] (uart_write+0x38/0xe0) [<802f5754>] (uart_write+0x38/0xe0) from [<80455270>] (hci_uart_tx_wakeup+0xa4/0x168) [<80455270>] (hci_uart_tx_wakeup+0xa4/0x168) from [<802dab18>] (tty_wakeup+0x50/0x5c) [<802dab18>] (tty_wakeup+0x50/0x5c) from [<802f81a4>] (imx_rtsint+0x50/0x80) [<802f81a4>] (imx_rtsint+0x50/0x80) from [<802f88f4>] (imx_int+0x158/0x17c) [<802f88f4>] (imx_int+0x158/0x17c) from [<8007abe0>] (handle_irq_event_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 to implemet the @write_wakeup should follow the limits which avoid the deadlock. Signed-off-by: Huang Shijie Signed-off-by: Felipe Balbi --- include/linux/tty_ldisc.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h index add26da..00c9d68 100644 --- a/include/linux/tty_ldisc.h +++ b/include/linux/tty_ldisc.h @@ -92,7 +92,10 @@ * 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 *) * -- 1.9.2.459.g68773ac -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html