Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752840Ab2HMAAQ (ORCPT ); Sun, 12 Aug 2012 20:00:16 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:57980 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752584Ab2HMAAN (ORCPT ); Sun, 12 Aug 2012 20:00:13 -0400 Message-ID: <50284383.7020100@gmail.com> Date: Mon, 13 Aug 2012 10:00:03 +1000 From: Ryan Mallon User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120714 Thunderbird/14.0 MIME-Version: 1.0 To: David Herrmann CC: linux-fbdev@vger.kernel.org, Florian Tobias Schandinat , Greg Kroah-Hartman , linux-serial@vger.kernel.org, Alan Cox , linux-kernel@vger.kernel.org, Geert Uytterhoeven Subject: Re: [PATCH 06/11] fblog: open fb on registration References: <1344783205-2384-1-git-send-email-dh.herrmann@googlemail.com> <1344783205-2384-7-git-send-email-dh.herrmann@googlemail.com> In-Reply-To: <1344783205-2384-7-git-send-email-dh.herrmann@googlemail.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6131 Lines: 212 On 13/08/12 00:53, David Herrmann wrote: > This opens the framebuffer upon registration so we can use it for > drawing-operations. On unregistration we close it again. > > While opening/closing or accessing the fb in any other way, we must hold > the fb-mutex. However, since the notifiers are often called with the mutex > already held, we cannot lock it _after_ taking the > fblog_registration_lock. Therefore, we require the caller to make sure the > fb-mutex is held. > > Signed-off-by: David Herrmann Some comments below, ~Ryan > --- > drivers/video/console/fblog.c | 94 ++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 93 insertions(+), 1 deletion(-) > > diff --git a/drivers/video/console/fblog.c b/drivers/video/console/fblog.c > index 279f4d8..1c526c5 100644 > --- a/drivers/video/console/fblog.c > +++ b/drivers/video/console/fblog.c > @@ -32,12 +32,14 @@ > > enum fblog_flags { > FBLOG_KILLED, > + FBLOG_OPEN, > }; > > struct fblog_fb { > unsigned long flags; > struct fb_info *info; > struct device dev; > + struct mutex lock; > }; > > static DEFINE_MUTEX(fblog_registration_lock); > @@ -46,6 +48,74 @@ static struct fblog_fb *fblog_fbs[FB_MAX]; > #define to_fblog_dev(_d) container_of(_d, struct fblog_fb, dev) > > /* > + * fblog_open/close() > + * These functions manage access to the underlying framebuffer. While opened, we > + * have a valid reference to the fb and can use it for drawing operations. When > + * the fb is unregistered, we drop our reference and close the fb so it can get > + * deleted properly. We also mark it as dead so no further fblog_open() call > + * will succeed. > + * Both functions must be called with the fb->info->lock mutex held! But make > + * sure to lock it _before_ locking the fblog-registration-lock. Otherwise, we > + * will dead-lock with fb-registration. > + */ > + > +static int fblog_open(struct fblog_fb *fb) > +{ > + int ret; > + > + mutex_lock(&fb->lock); > + > + if (test_bit(FBLOG_KILLED, &fb->flags)) { > + ret = -ENODEV; > + goto unlock; > + } > + > + if (test_bit(FBLOG_OPEN, &fb->flags)) { > + ret = 0; > + goto unlock; > + } > + > + if (!try_module_get(fb->info->fbops->owner)) { > + ret = -ENODEV; > + goto out_killed; > + } > + > + if (fb->info->fbops->fb_open && fb->info->fbops->fb_open(fb->info, 0)) { Should propagate the error here: if (fb->info->fbops->fb_open) { ret = fb->info->fbops->fb_open(fb->info, 0); if (ret) gotou out_unref; } > + ret = -EIO; > + goto out_unref; > + } > + > + set_bit(FBLOG_OPEN, &fb->flags); > + mutex_unlock(&fb->lock); > + return 0; > + > +out_unref: > + module_put(fb->info->fbops->owner); > +out_killed: > + set_bit(FBLOG_KILLED, &fb->flags); > +unlock: > + mutex_unlock(&fb->lock); > + return ret; > +} > + > +static void fblog_close(struct fblog_fb *fb, bool kill_dev) > +{ > + mutex_lock(&fb->lock); > + > + if (test_bit(FBLOG_OPEN, &fb->flags)) { > + if (fb->info->fbops->fb_release) > + fb->info->fbops->fb_release(fb->info, 0); > + module_put(fb->info->fbops->owner); > + clear_bit(FBLOG_OPEN, &fb->flags); > + } > + > + if (kill_dev) > + set_bit(FBLOG_KILLED, &fb->flags); > + > + mutex_unlock(&fb->lock); > +} > + > +/* > * fblog framebuffer list > * The fblog_fbs[] array contains all currently registered framebuffers. If a > * framebuffer is in that list, we always must make sure that we own a reference > @@ -77,6 +147,7 @@ static void fblog_do_unregister(struct fb_info *info) > > fblog_fbs[info->node] = NULL; > > + fblog_close(fb, true); > device_del(&fb->dev); > put_device(&fb->dev); device_unregister? > } > @@ -99,6 +170,7 @@ static void fblog_do_register(struct fb_info *info, bool force) > return; > > fb->info = info; > + mutex_init(&fb->lock); > __module_get(THIS_MODULE); > device_initialize(&fb->dev); > fb->dev.class = fb_class; > @@ -113,6 +185,8 @@ static void fblog_do_register(struct fb_info *info, bool force) > put_device(&fb->dev); > return; > } > + > + fblog_open(fb); > } This function should really return an errno value. > > static void fblog_register(struct fb_info *info, bool force) > @@ -134,6 +208,7 @@ static int fblog_event(struct notifier_block *self, unsigned long action, > { > struct fb_event *event = data; > struct fb_info *info = event->info; > + struct fblog_fb *fb; > > switch(action) { > case FB_EVENT_FB_REGISTERED: > @@ -145,8 +220,21 @@ static int fblog_event(struct notifier_block *self, unsigned long action, > case FB_EVENT_FB_UNREGISTERED: > /* This is called when a low-level system driver unregisters a > * framebuffer. The registration lock is held but the console > - * lock might not be held. */ > + * lock might not be held. The fb-lock is not held, either! */ > + mutex_lock(&info->lock); > fblog_unregister(info); > + mutex_unlock(&info->lock); > + break; > + case FB_EVENT_FB_UNBIND: > + /* Called directly before unregistering an FB. The FB is still > + * valid here and the registration lock is held but the console > + * lock might not be held (really?). */ > + mutex_lock(&fblog_registration_lock); > + fb = fblog_fbs[info->node]; > + mutex_unlock(&fblog_registration_lock); > + > + if (fb) > + fblog_close(fb, true); > break; > } > > @@ -163,7 +251,9 @@ static void fblog_scan(void) > if (!info || IS_ERR(info)) > continue; > > + mutex_lock(&info->lock); > fblog_register(info, false); > + mutex_unlock(&info->lock); > > /* There is a very subtle race-condition. Even though we might > * own a reference to the fb, it may still get unregistered > @@ -224,7 +314,9 @@ static void __exit fblog_exit(void) > if (!info || IS_ERR(info)) > continue; > > + mutex_lock(&info->lock); > fblog_unregister(info); > + mutex_unlock(&info->lock); > put_fb_info(info); > } > } > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/