From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from nm1-vm0.bt.bullet.mail.ird.yahoo.com ([212.82.108.94]:41778 "HELO nm1-vm0.bt.bullet.mail.ird.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751270Ab1HPIzX (ORCPT ); Tue, 16 Aug 2011 04:55:23 -0400 Received: from volcano.underworld (volcano.underworld [192.168.0.3]) by wellhouse.underworld (8.14.3/8.14.3/Debian-5+lenny1) with ESMTP id p7G8o1cp031143 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT) for ; Tue, 16 Aug 2011 09:50:03 +0100 Message-ID: <4E4A2F39.6090809@yahoo.com> Date: Tue, 16 Aug 2011 09:50:01 +0100 From: Chris Rankin MIME-Version: 1.0 To: linux-media@vger.kernel.org Subject: [PATCH] Fix locking problem between em28xx and em28xx-dvb modules Content-Type: multipart/mixed; boundary="------------020104090104070107080301" Sender: linux-media-owner@vger.kernel.org List-ID: This is a multi-part message in MIME format. --------------020104090104070107080301 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Hi, I've thought about this patch a bit more overnight, and it occurred to me that while em28xx_init_extension() now takes the device mutex followed by the device list mutex, my original fix would have had em28xx_register_extension() taking the device list mutex followed by the device mutex. And that sounds suspiciously like a potential deadlock to me. So I was wondering: does em28xx_register_extension() actually need to lock the device if the device list has already been locked? I've also moved two printk()s outside the region where we hold the device list mutex, because locked bits should be as brief as possible and neither printk() does anything that needs the lock. A new patch is attached, for review. Signed-off-by: Chris Rankin --------------020104090104070107080301 Content-Type: text/x-patch; name="EM28xx-DVB.diff" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="EM28xx-DVB.diff" --- linux-3.0/drivers/media/video/em28xx/em28xx-core.c.orig 2011-08-16 09:15:46.000000000 +0100 +++ linux-3.0/drivers/media/video/em28xx/em28xx-core.c 2011-08-16 09:21:08.000000000 +0100 @@ -1193,8 +1193,8 @@ list_for_each_entry(dev, &em28xx_devlist, devlist) { ops->init(dev); } - printk(KERN_INFO "Em28xx: Initialized (%s) extension\n", ops->name); mutex_unlock(&em28xx_devlist_mutex); + printk(KERN_INFO "Em28xx: Initialized (%s) extension\n", ops->name); return 0; } EXPORT_SYMBOL(em28xx_register_extension); @@ -1207,9 +1207,9 @@ list_for_each_entry(dev, &em28xx_devlist, devlist) { ops->fini(dev); } - printk(KERN_INFO "Em28xx: Removed (%s) extension\n", ops->name); list_del(&ops->next); mutex_unlock(&em28xx_devlist_mutex); + printk(KERN_INFO "Em28xx: Removed (%s) extension\n", ops->name); } EXPORT_SYMBOL(em28xx_unregister_extension); --- linux-3.0/drivers/media/video/em28xx/em28xx-dvb.c.orig 2011-08-16 09:16:03.000000000 +0100 +++ linux-3.0/drivers/media/video/em28xx/em28xx-dvb.c 2011-08-16 09:17:06.000000000 +0100 @@ -542,7 +542,6 @@ dev->dvb = dvb; dvb->fe[0] = dvb->fe[1] = NULL; - mutex_lock(&dev->lock); em28xx_set_mode(dev, EM28XX_DIGITAL_MODE); /* init frontend */ switch (dev->model) { @@ -711,7 +710,6 @@ em28xx_info("Successfully loaded em28xx-dvb\n"); ret: em28xx_set_mode(dev, EM28XX_SUSPEND); - mutex_unlock(&dev->lock); return result; out_free: --------------020104090104070107080301--