From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754362AbdCWRh1 (ORCPT ); Thu, 23 Mar 2017 13:37:27 -0400 Received: from bny206.haproxy.com ([37.58.153.206]:53042 "EHLO smtp.exceliance.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751929AbdCWRh0 (ORCPT ); Thu, 23 Mar 2017 13:37:26 -0400 X-Greylist: delayed 1336 seconds by postgrey-1.27 at vger.kernel.org; Thu, 23 Mar 2017 13:37:26 EDT Date: Thu, 23 Mar 2017 18:37:18 +0100 From: Willy TARREAU To: Geert Uytterhoeven Cc: Miguel Ojeda Sandonis , Greg Kroah-Hartman , Ksenija Stanojevic , Arnd Bergmann , linux-kernel@vger.kernel.org Subject: Re: [PATCH 00/13] Add HD44780 Character LCD support Message-ID: <20170323173718.GA9942@haproxy.com> References: <1486391895-9554-1-git-send-email-geert@linux-m68k.org> <20170323171501.GI9408@haproxy.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170323171501.GI9408@haproxy.com> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi again, On Thu, Mar 23, 2017 at 06:15:01PM +0100, Willy TARREAU wrote: > So I finally had the time to give it a try by applying your patchset > on top of our 4.9 prod kernel. For now I'm getting a panic at boot : > > BUG: unable to handle kernel NULL pointer dereference at (null) > IP: [] __mutex_lock_slowpath+0x6d/0x100 (...) It was indeed related to the backlight mutex. It's initialized after charlcd_init_display() succeeds, but the backlight is touched within this function. I just moved it upwards and that solved the issue. Feel free to re-integrate this (or an equivalent) into your patch. With only this fix, everything works fine here without even having to touch the configuration, good job! Thanks! Willy -- diff --git a/drivers/auxdisplay/charlcd.c b/drivers/auxdisplay/charlcd.c index 6aea900..e7f1bfe 100644 --- a/drivers/auxdisplay/charlcd.c +++ b/drivers/auxdisplay/charlcd.c @@ -703,6 +703,8 @@ static int charlcd_init(struct charlcd *lcd) struct charlcd_priv *priv = to_priv(lcd); int ret; + mutex_init(&priv->bl_tempo_lock); + /* * before this line, we must NOT send anything to the display. * Since charlcd_init_display() needs to write data, we have to @@ -713,7 +715,6 @@ static int charlcd_init(struct charlcd *lcd) return ret; if (lcd->ops->backlight) { - mutex_init(&priv->bl_tempo_lock); INIT_DELAYED_WORK(&priv->bl_work, charlcd_bl_off); }