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Date: Tue, 15 Jan 2013 17:46:51 +0100
From: Takashi Iwai <tiwai@...e.de>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: sedat.dilek@...il.com, Jiri Kosina <jkosina@...e.cz>,
linux-fbdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
alan@...rguk.ukuu.org.uk
Subject: Re: 3.8-rc2 lockdep complains about console_lock vs. fb_notifier_list.rwsem
At Tue, 15 Jan 2013 15:47:18 +0100,
Takashi Iwai wrote:
>
> At Tue, 15 Jan 2013 15:25:18 +0100,
> Takashi Iwai wrote:
> >
> > At Sat, 5 Jan 2013 13:13:27 +0100,
> > Sedat Dilek wrote:
> > >
> > > Hi Jiri,
> > >
> > > ...known issue (see thread in [1]), please feel free to test patches
> > > from Alan and Andrew (see [1], [2] and [3]) and report.
> > >
> > > Regards,
> > > - Sedat -
> > >
> > > [1] http://marc.info/?t=135309396400003&r=1&w=2
> > > [2] http://ozlabs.org/~akpm/mmots/broken-out/fb-rework-locking-to-fix-lock-ordering-on-takeover.patch
> > > [3] http://ozlabs.org/~akpm/mmots/broken-out/fb-rework-locking-to-fix-lock-ordering-on-takeover-fix.patch
> > > [4] http://ozlabs.org/~akpm/mmots/broken-out/fb-rework-locking-to-fix-lock-ordering-on-takeover-fix-2.patch
> >
> > I've hit this bug and tried the patch [2] ([3] and [4] are gone).
> > Unfortunately the deadlock is still reported, as seen below.
> >
> > A similar fix for fbcon_unbind(), splitting an unlocked version of
> > unbind_con_driver() and call it?
> >
> > (BTW, the patch [2] contains strange characters in the comments, and
> > has a few coding issues easily detected by checkpatch.pl.)
>
> The fix patch for coding issue is below.
> Feel free to fold into the original patch.
... and the additional patch below fixed the lockdep warning on my
machine.
Takashi
===
From: Takashi Iwai <tiwai@...e.de>
Subject: [PATCH] fb: Yet another band-aid for fixing lockdep mess
I've still got lockdep warnings even after Alan's patch, and it seems
that yet more band aids are required to paper over similar paths for
unbind_con_driver() and unregister_con_driver(). After this hack,
lockdep warnings are finally gone.
Signed-off-by: Takashi Iwai <tiwai@...e.de>
---
drivers/tty/vt/vt.c | 43 ++++++++++++++++++++++++++++---------------
drivers/video/console/fbcon.c | 4 ++--
drivers/video/fbmem.c | 4 ++++
include/linux/console.h | 1 +
include/linux/vt_kern.h | 2 ++
5 files changed, 37 insertions(+), 17 deletions(-)
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 1db1c8d..3947e8d 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -3135,6 +3135,18 @@ static int con_is_graphics(const struct consw *csw, int first, int last)
*/
int unbind_con_driver(const struct consw *csw, int first, int last, int deflt)
{
+ int retval;
+
+ console_lock();
+ retval = do_unbind_con_driver(csw, first, last, deflt);
+ console_unlock();
+ return retval;
+}
+EXPORT_SYMBOL(unbind_con_driver);
+
+/* unlocked version of unbind_con_driver() */
+int do_unbind_con_driver(const struct consw *csw, int first, int last, int deflt)
+{
struct module *owner = csw->owner;
const struct consw *defcsw = NULL;
struct con_driver *con_driver = NULL, *con_back = NULL;
@@ -3143,7 +3155,7 @@ int unbind_con_driver(const struct consw *csw, int first, int last, int deflt)
if (!try_module_get(owner))
return -ENODEV;
- console_lock();
+ WARN_CONSOLE_UNLOCKED();
/* check if driver is registered and if it is unbindable */
for (i = 0; i < MAX_NR_CON_DRIVER; i++) {
@@ -3156,10 +3168,8 @@ int unbind_con_driver(const struct consw *csw, int first, int last, int deflt)
}
}
- if (retval) {
- console_unlock();
+ if (retval)
goto err;
- }
retval = -ENODEV;
@@ -3175,15 +3185,11 @@ int unbind_con_driver(const struct consw *csw, int first, int last, int deflt)
}
}
- if (retval) {
- console_unlock();
+ if (retval)
goto err;
- }
- if (!con_is_bound(csw)) {
- console_unlock();
+ if (!con_is_bound(csw))
goto err;
- }
first = max(first, con_driver->first);
last = min(last, con_driver->last);
@@ -3212,13 +3218,12 @@ int unbind_con_driver(const struct consw *csw, int first, int last, int deflt)
/* ignore return value, binding should not fail */
do_bind_con_driver(defcsw, first, last, deflt);
- console_unlock();
err:
module_put(owner);
return retval;
}
-EXPORT_SYMBOL(unbind_con_driver);
+EXPORT_SYMBOL_GPL(do_unbind_con_driver);
static int vt_bind(struct con_driver *con)
{
@@ -3605,9 +3610,18 @@ EXPORT_SYMBOL(register_con_driver);
*/
int unregister_con_driver(const struct consw *csw)
{
- int i, retval = -ENODEV;
+ int retval;
console_lock();
+ retval = do_unregister_con_driver(csw);
+ console_unlock();
+ return retval;
+}
+EXPORT_SYMBOL(unregister_con_driver);
+
+int do_unregister_con_driver(const struct consw *csw)
+{
+ int i, retval = -ENODEV;
/* cannot unregister a bound driver */
if (con_is_bound(csw))
@@ -3633,10 +3647,9 @@ int unregister_con_driver(const struct consw *csw)
}
}
err:
- console_unlock();
return retval;
}
-EXPORT_SYMBOL(unregister_con_driver);
+EXPORT_SYMBOL_GPL(do_unregister_con_driver);
/*
* If we support more console drivers, this function is used
diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
index 4bd7820..2aef9ca 100644
--- a/drivers/video/console/fbcon.c
+++ b/drivers/video/console/fbcon.c
@@ -3004,7 +3004,7 @@ static int fbcon_unbind(void)
{
int ret;
- ret = unbind_con_driver(&fb_con, first_fb_vc, last_fb_vc,
+ ret = do_unbind_con_driver(&fb_con, first_fb_vc, last_fb_vc,
fbcon_is_default);
if (!ret)
@@ -3077,7 +3077,7 @@ static int fbcon_fb_unregistered(struct fb_info *info)
primary_device = -1;
if (!num_registered_fb)
- unregister_con_driver(&fb_con);
+ do_unregister_con_driver(&fb_con);
return 0;
}
diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
index d8d9831..070b9a1 100644
--- a/drivers/video/fbmem.c
+++ b/drivers/video/fbmem.c
@@ -1668,8 +1668,10 @@ static int do_unregister_framebuffer(struct fb_info *fb_info)
if (!lock_fb_info(fb_info))
return -ENODEV;
+ console_lock();
event.info = fb_info;
ret = fb_notifier_call_chain(FB_EVENT_FB_UNBIND, &event);
+ console_unlock();
unlock_fb_info(fb_info);
if (ret)
@@ -1684,7 +1686,9 @@ static int do_unregister_framebuffer(struct fb_info *fb_info)
num_registered_fb--;
fb_cleanup_device(fb_info);
event.info = fb_info;
+ console_lock();
fb_notifier_call_chain(FB_EVENT_FB_UNREGISTERED, &event);
+ console_unlock();
/* this may free fb info */
put_fb_info(fb_info);
diff --git a/include/linux/console.h b/include/linux/console.h
index 4ef4307..47b858c 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -77,6 +77,7 @@ extern const struct consw prom_con; /* SPARC PROM console */
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 do_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);
diff --git a/include/linux/vt_kern.h b/include/linux/vt_kern.h
index 50ae7d0..dbbc6bf 100644
--- a/include/linux/vt_kern.h
+++ b/include/linux/vt_kern.h
@@ -130,6 +130,8 @@ void vt_event_post(unsigned int event, unsigned int old, unsigned int new);
int vt_waitactive(int n);
void change_console(struct vc_data *new_vc);
void reset_vc(struct vc_data *vc);
+extern int do_unbind_con_driver(const struct consw *csw, int first, int last,
+ int deflt);
extern int unbind_con_driver(const struct consw *csw, int first, int last,
int deflt);
int vty_init(const struct file_operations *console_fops);
--
1.8.1
--
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