From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Subject: Re: [PATCH resend] serial_core: Fix pm imbalance on unbind Date: Fri, 21 Mar 2014 18:41:19 -0400 Message-ID: <532CC00F.3000501@hurleysoftware.com> References: <1395392905-29569-1-git-send-email-geert@linux-m68k.org> <532C394A.3050408@hurleysoftware.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-sh-owner@vger.kernel.org To: Geert Uytterhoeven Cc: Greg Kroah-Hartman , Jiri Slaby , linux-serial@vger.kernel.org, Linux-sh list , "linux-kernel@vger.kernel.org" , Geert Uytterhoeven List-Id: linux-serial@vger.kernel.org Hi Geert, On 03/21/2014 09:23 AM, Geert Uytterhoeven wrote: > Hi Peter, > > On Fri, Mar 21, 2014 at 2:06 PM, Peter Hurley wrote: >>> @@ -2681,10 +2683,12 @@ int uart_remove_one_port(struct uart_driver *drv, >>> struct uart_port *uport) >>> } >>> >>> /* >>> - * If the port is used as a console, unregister it >>> + * If the port is used as a console, unregister it, and power it >>> down >>> */ >>> - if (uart_console(uport)) >>> + if (uart_console(uport)) { >>> unregister_console(uport->cons); >>> + uart_change_pm(state, UART_PM_STATE_OFF); >> >> Won't this power off the port while tty consoles may still be open? > > I didn't see that actually happening. Ok, but I still think this isn't right. See below. >> I think the right thing here is to unregister_console then set uport->cons = >> NULL >> >> [uport->cons is properly reassigned when/if a port is re-added via >> uart_add_one_port()).] > > But indeed, for concistency/symmetry uport->state and uport->cons > should be resend, but that's something separate. I don't see this as being a "looks good" problem; I see this as being "what's the right way to teardown a uart device that's going away when a tty console is running on it", and there are too many problems with uart_remove_one_port() doing: state->uart_port = NULL to keep with that solution. >> Then, uart_close() will power off the port when all ttys using the port have >> been closed. > > uart_close() won't get that far, so uart_change_pm() won't be called. And this is the central problem: uart_close() must complete normally if a tty console is still running on a device. For example, if uart_shutdown() isn't getting called, then who's freeing the ring buffer page? > See also https://lkml.org/lkml/2014/3/10/651, and my workaround for the > crash https://lkml.org/lkml/2014/3/17/231. See my comments to the v2 patch there. Regards, Peter Hurley