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Date: Wed, 7 Nov 2012 16:02:32 +0000
From: Alan Cox <alan@...rguk.ukuu.org.uk>
To: Sasha Levin <levinsasha928@...il.com>
Cc: Dave Jones <davej@...hat.com>, Hugh Dickins <hughd@...gle.com>,
Sasha Levin <sasha.levin@...cle.com>,
Daniel Vetter <daniel.vetter@...ll.ch>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
linux-fbdev@...r.kernel.org, florianSchandinat@....de
Subject: Re: tty, vt: lockdep warnings
On Wed, 07 Nov 2012 08:47:08 -0500
Sasha Levin <levinsasha928@...il.com> wrote:
> On 11/06/2012 12:38 PM, Alan Cox wrote:
> >> > The root
> >> > cause is loading two different framebuffers with one taking over from
> >> > another - that should be an obscure corner case and once the fuzz testing
> >> > can avoid.
> >> >
> >> > I had a semi-informed poke at this and came up with a possible patch (not very tested)
> >>
> >> If this fixes the real problems we've been seeing, I'll dance a jig.
> >
> > Youtube...
>
> +1
>
> > At this point my bigger concern is that it'll just make something else
> > warn instead. The underlying problem is that fbcon layer implements a
> > single threaded notifier whose locking semantics are at best random. It's
> > not calld with a specific set of locks each time. Possibly it sohuld be
> > two notifiers (one for fb stuff, one for console layer stuff) but the
> > entire layer is horrible. I live in home the KMS guys will rip out the
> > useful bits and build a straight kms fb layer with refcounting and the
> > like 8)
> >
> > Testing certainly needed and if it's still blowing up then hopefully
> > further traces will help fix up the other cases we don't know about.
>
> So the good news are that the original lockdep splat I've reported is gone.
>
> The semi-bad news are that there's a new one. It happens less frequently
> but I assume it's not a new splat either, but was well hidden behind the
> other splat.
Doesn't look too bad (fingers crossed)
try
commit 8f965b0816d98ed535fdfccc3e50d84818e9c43b
Author: Alan Cox <alan@...ux.intel.com>
Date: Wed Nov 7 15:48:48 2012 +0000
fb: Rework locking to fix lock ordering on takeover
Adjust the console layer to allow a take over call where the caller already
holds the locks. Make the fb layer lock in order.
This s partly a band aid, the fb layer is terminally confused about the
locking rules it uses for its notifiers it seems.
Signed-off-by: Alan Cox <alan@...ux.intel.com>
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index f87d7e8..ea57f27 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -2984,7 +2984,7 @@ int __init vty_init(const struct file_operations *console_fops)
static struct class *vtconsole_class;
-static int bind_con_driver(const struct consw *csw, int first, int last,
+static int do_bind_con_driver(const struct consw *csw, int first, int last,
int deflt)
{
struct module *owner = csw->owner;
@@ -2995,7 +2995,7 @@ static int bind_con_driver(const struct consw *csw, int first, int last,
if (!try_module_get(owner))
return -ENODEV;
- console_lock();
+ WARN_CONSOLE_UNLOCKED();
/* check if driver is registered */
for (i = 0; i < MAX_NR_CON_DRIVER; i++) {
@@ -3080,11 +3080,22 @@ static int bind_con_driver(const struct consw *csw, int first, int last,
retval = 0;
err:
- console_unlock();
module_put(owner);
return retval;
};
+
+static int bind_con_driver(const struct consw *csw, int first, int last,
+ int deflt)
+{
+ int ret;
+
+ console_unlock();
+ ret = do_bind_con_driver(csw, first, last, deflt);
+ console_unlock();
+ return ret;
+}
+
#ifdef CONFIG_VT_HW_CONSOLE_BINDING
static int con_is_graphics(const struct consw *csw, int first, int last)
{
@@ -3196,9 +3207,9 @@ int unbind_con_driver(const struct consw *csw, int first, int last, int deflt)
if (!con_is_bound(csw))
con_driver->flag &= ~CON_DRIVER_FLAG_INIT;
- console_unlock();
/* ignore return value, binding should not fail */
- bind_con_driver(defcsw, first, last, deflt);
+ do_bind_con_driver(defcsw, first, last, deflt);
+ console_unlock();
err:
module_put(owner);
return retval;
@@ -3489,28 +3500,18 @@ int con_debug_leave(void)
}
EXPORT_SYMBOL_GPL(con_debug_leave);
-/**
- * register_con_driver - register console driver to console layer
- * @csw: console driver
- * @first: the first console to take over, minimum value is 0
- * @last: the last console to take over, maximum value is MAX_NR_CONSOLES -1
- *
- * DESCRIPTION: This function registers a console driver which can later
- * bind to a range of consoles specified by @first and @last. It will
- * also initialize the console driver by calling con_startup().
- */
-int register_con_driver(const struct consw *csw, int first, int last)
+static int do_register_con_driver(const struct consw *csw, int first, int last)
{
struct module *owner = csw->owner;
struct con_driver *con_driver;
const char *desc;
int i, retval = 0;
+ WARN_CONSOLE_UNLOCKED();
+
if (!try_module_get(owner))
return -ENODEV;
- console_lock();
-
for (i = 0; i < MAX_NR_CON_DRIVER; i++) {
con_driver = ®istered_con_driver[i];
@@ -3563,10 +3564,29 @@ int register_con_driver(const struct consw *csw, int first, int last)
}
err:
- console_unlock();
module_put(owner);
return retval;
}
+
+/**
+ * register_con_driver - register console driver to console layer
+ * @csw: console driver
+ * @first: the first console to take over, minimum value is 0
+ * @last: the last console to take over, maximum value is MAX_NR_CONSOLES -1
+ *
+ * DESCRIPTION: This function registers a console driver which can later
+ * bind to a range of consoles specified by @first and @last. It will
+ * also initialize the console driver by calling con_startup().
+ */
+int register_con_driver(const struct consw *csw, int first, int last)
+{
+ int retval;
+
+ console_lock();
+ retval = do_register_con_driver(csw, first, last);
+ console_unlock();
+ return retval;
+}
EXPORT_SYMBOL(register_con_driver);
/**
@@ -3622,6 +3642,29 @@ EXPORT_SYMBOL(unregister_con_driver);
*
* take_over_console is basically a register followed by unbind
*/
+int do_take_over_console(const struct consw *csw, int first, int last, int deflt)
+{
+ int err;
+
+ err = do_register_con_driver(csw, first, last);
+ /* if we get an busy error we still want to bind the console driver
+ * and return success, as we may have unbound the console driver
+ * but not unregistered it.
+ */
+ if (err == -EBUSY)
+ err = 0;
+ if (!err)
+ do_bind_con_driver(csw, first, last, deflt);
+
+ return err;
+}
+/*
+ * If we support more console drivers, this function is used
+ * when a driver wants to take over some existing consoles
+ * and become default driver for newly opened ones.
+ *
+ * take_over_console is basically a register followed by unbind
+ */
int take_over_console(const struct consw *csw, int first, int last, int deflt)
{
int err;
diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
index fdefa8f..c75f8ce 100644
--- a/drivers/video/console/fbcon.c
+++ b/drivers/video/console/fbcon.c
@@ -529,6 +529,34 @@ static int search_for_mapped_con(void)
return retval;
}
+static int do_fbcon_takeover(int show_logo)
+{
+ int err, i;
+
+ if (!num_registered_fb)
+ return -ENODEV;
+
+ if (!show_logo)
+ logo_shown = FBCON_LOGO_DONTSHOW;
+
+ for (i = first_fb_vc; i <= last_fb_vc; i++)
+ con2fb_map[i] = info_idx;
+
+ err = do_take_over_console(&fb_con, first_fb_vc, last_fb_vc,
+ fbcon_is_default);
+
+ if (err) {
+ for (i = first_fb_vc; i <= last_fb_vc; i++) {
+ con2fb_map[i] = -1;
+ }
+ info_idx = -1;
+ } else {
+ fbcon_has_console_bind = 1;
+ }
+
+ return err;
+}
+
static int fbcon_takeover(int show_logo)
{
int err, i;
@@ -3115,7 +3143,7 @@ static int fbcon_fb_registered(struct fb_info *info)
}
if (info_idx != -1)
- ret = fbcon_takeover(1);
+ ret = do_fbcon_takeover(1);
} else {
for (i = first_fb_vc; i <= last_fb_vc; i++) {
if (con2fb_map_boot[i] == idx)
diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
index 3ff0105..564ebe9 100644
--- a/drivers/video/fbmem.c
+++ b/drivers/video/fbmem.c
@@ -1650,7 +1650,9 @@ static int do_register_framebuffer(struct fb_info *fb_info)
event.info = fb_info;
if (!lock_fb_info(fb_info))
return -ENODEV;
+ console_lock();
fb_notifier_call_chain(FB_EVENT_FB_REGISTERED, &event);
+ console_unlock();
unlock_fb_info(fb_info);
return 0;
}
@@ -1853,11 +1855,8 @@ int fb_new_modelist(struct fb_info *info)
err = 1;
if (!list_empty(&info->modelist)) {
- if (!lock_fb_info(info))
- return -ENODEV;
event.info = info;
err = fb_notifier_call_chain(FB_EVENT_NEW_MODELIST, &event);
- unlock_fb_info(info);
}
return err;
diff --git a/drivers/video/fbsysfs.c b/drivers/video/fbsysfs.c
index a55e366..ef476b0 100644
--- a/drivers/video/fbsysfs.c
+++ b/drivers/video/fbsysfs.c
@@ -177,6 +177,8 @@ static ssize_t store_modes(struct device *device,
if (i * sizeof(struct fb_videomode) != count)
return -EINVAL;
+ if (!lock_fb_info(fb_info))
+ return -ENODEV;
console_lock();
list_splice(&fb_info->modelist, &old_list);
fb_videomode_to_modelist((const struct fb_videomode *)buf, i,
@@ -188,6 +190,7 @@ static ssize_t store_modes(struct device *device,
fb_destroy_modelist(&old_list);
console_unlock();
+ unlock_fb_info(fb_info);
return 0;
}
diff --git a/include/linux/console.h b/include/linux/console.h
index dedb082..4ef4307 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -78,6 +78,7 @@ int con_is_bound(const struct consw *csw);
int register_con_driver(const struct consw *csw, int first, int last);
int unregister_con_driver(const struct consw *csw);
int take_over_console(const struct consw *sw, int first, int last, int deflt);
+int do_take_over_console(const struct consw *sw, int first, int last, int deflt);
void give_up_console(const struct consw *sw);
#ifdef CONFIG_HW_CONSOLE
int con_debug_enter(struct vc_data *vc);
--
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