From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Subject: Re: [PATCH 1/3] serial: 8250: unlock port for uart_write_wakeup() Date: Thu, 30 Jul 2015 19:15:23 -0400 Message-ID: <55BAB00B.3010806@hurleysoftware.com> References: <87h9ol2r4y.fsf@linutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <87h9ol2r4y.fsf@linutronix.de> Sender: linux-kernel-owner@vger.kernel.org To: John Ogness , linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , Tony Lindgren , Sebastian Andrzej Siewior , linux-omap@vger.kernel.org, nsekhar@ti.com, nm@ti.com, linux-serial@vger.kernel.org List-Id: linux-omap@vger.kernel.org On 07/30/2015 06:54 PM, John Ogness wrote: > uart_write_wakeup() should be called without holding the port lock. > Otherwise a possible recursive spinlock issue can occur, such as > the following callchain: > > 8250_core.c:serial8250_tx_chars() - called with port locked > serial_core.c:uart_write_wakeup() > tty_io.c:tty_wakeup() > st_core.c:st_tty_wakeup() > st_core.c:st_tx_wakeup() > st_core.c:st_int_write() > serial_core.c:uart_write() - locks port NAK. This is a bug in the N_TI_WL line discipline, specifically in the st_tx_wakeup() function, which cannot perform the write synchronously. This is a common line discipline bug, and typically fixed by performing the wakeup operations from a kworker instead. Regards, Peter Hurley