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Date: Thu, 5 Feb 2009 00:58:30 +0100
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: Andrea Righi <righi.andrea@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Andrey Borzenkov <arvidjaar@...l.ru>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
"Antonino A. Daplas" <adaplas@...il.com>,
linux-fbdev-devel@...ts.sourceforge.net,
linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
Dave Jones <davej@...hat.com>,
Harvey Harrison <harvey.harrison@...il.com>,
Johannes Weiner <hannes@...xchg.org>,
Stefan Richter <stefanr@...6.in-berlin.de>
Subject: Re: [PATCH -mmotm] fbmem: fix fb_info->lock and mm->mmap_sem circular locking dependency
On Wednesday 04 February 2009, Andrea Righi wrote:
> Fix this circular locking dependencies in the frame buffer console
> driver pushing down the mutex fb_info->lock.
>
> Circular locking dependecies occur calling the blocking
> fb_notifier_call_chain() with fb_info->lock held. Notifier callbacks can
> try to acquire mm->mmap_sem, while fb_mmap() acquires the locks in the
> reverse order mm->mmap_sem => fb_info->lock.
Does this fix a Bugzilla bug? If so, then which one?
> Tested-by: Andrey Borzenkov <arvidjaar@...l.ru>
> Signed-off-by: Andrea Righi <righi.andrea@...il.com>
> ---
> drivers/video/backlight/backlight.c | 3 +
> drivers/video/backlight/lcd.c | 3 +
> drivers/video/console/fbcon.c | 73 ++++++++++++++++++++++++++++++-----
> drivers/video/fbmem.c | 11 +-----
> 4 files changed, 70 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
> index 157057c..dd37cbc 100644
> --- a/drivers/video/backlight/backlight.c
> +++ b/drivers/video/backlight/backlight.c
> @@ -35,6 +35,8 @@ static int fb_notifier_callback(struct notifier_block *self,
> return 0;
>
> bd = container_of(self, struct backlight_device, fb_notif);
> + if (!lock_fb_info(evdata->info))
> + return -ENODEV;
> mutex_lock(&bd->ops_lock);
> if (bd->ops)
> if (!bd->ops->check_fb ||
> @@ -47,6 +49,7 @@ static int fb_notifier_callback(struct notifier_block *self,
> backlight_update_status(bd);
> }
> mutex_unlock(&bd->ops_lock);
> + unlock_fb_info(evdata->info);
> return 0;
> }
>
> diff --git a/drivers/video/backlight/lcd.c b/drivers/video/backlight/lcd.c
> index b644947..0bb13df 100644
> --- a/drivers/video/backlight/lcd.c
> +++ b/drivers/video/backlight/lcd.c
> @@ -40,6 +40,8 @@ static int fb_notifier_callback(struct notifier_block *self,
> if (!ld->ops)
> return 0;
>
> + if (!lock_fb_info(evdata->info))
> + return -ENODEV;
> mutex_lock(&ld->ops_lock);
> if (!ld->ops->check_fb || ld->ops->check_fb(ld, evdata->info)) {
> if (event == FB_EVENT_BLANK) {
> @@ -51,6 +53,7 @@ static int fb_notifier_callback(struct notifier_block *self,
> }
> }
> mutex_unlock(&ld->ops_lock);
> + unlock_fb_info(evdata->info);
> return 0;
> }
>
> diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
> index 1657b96..2cd500a 100644
> --- a/drivers/video/console/fbcon.c
> +++ b/drivers/video/console/fbcon.c
> @@ -2954,8 +2954,11 @@ static int fbcon_fb_unbind(int idx)
>
> static int fbcon_fb_unregistered(struct fb_info *info)
> {
> - int i, idx = info->node;
> + int i, idx;
>
> + if (!lock_fb_info(info))
> + return -ENODEV;
> + idx = info->node;
> for (i = first_fb_vc; i <= last_fb_vc; i++) {
> if (con2fb_map[i] == idx)
> con2fb_map[i] = -1;
> @@ -2979,13 +2982,14 @@ static int fbcon_fb_unregistered(struct fb_info *info)
> }
> }
>
> - if (!num_registered_fb)
> - unregister_con_driver(&fb_con);
> -
> -
> if (primary_device == idx)
> primary_device = -1;
>
> + unlock_fb_info(info);
> +
> + if (!num_registered_fb)
> + unregister_con_driver(&fb_con);
> +
> return 0;
> }
>
> @@ -3021,9 +3025,13 @@ static inline void fbcon_select_primary(struct fb_info *info)
>
> static int fbcon_fb_registered(struct fb_info *info)
> {
> - int ret = 0, i, idx = info->node;
> + int ret = 0, i, idx;
>
> + if (!lock_fb_info(info))
> + return -ENODEV;
> + idx = info->node;
> fbcon_select_primary(info);
> + unlock_fb_info(info);
>
> if (info_idx == -1) {
> for (i = first_fb_vc; i <= last_fb_vc; i++) {
> @@ -3124,7 +3132,7 @@ static void fbcon_get_requirement(struct fb_info *info,
> }
> }
>
> -static int fbcon_event_notify(struct notifier_block *self,
> +static int fbcon_event_notify(struct notifier_block *self,
> unsigned long action, void *data)
> {
> struct fb_event *event = data;
> @@ -3132,7 +3140,7 @@ static int fbcon_event_notify(struct notifier_block *self,
> struct fb_videomode *mode;
> struct fb_con2fbmap *con2fb;
> struct fb_blit_caps *caps;
> - int ret = 0;
> + int idx, ret = 0;
>
> /*
> * ignore all events except driver registration and deregistration
> @@ -3144,23 +3152,54 @@ static int fbcon_event_notify(struct notifier_block *self,
>
> switch(action) {
> case FB_EVENT_SUSPEND:
> + if (!lock_fb_info(info)) {
> + ret = -ENODEV;
> + goto done;
> + }
> fbcon_suspended(info);
> + unlock_fb_info(info);
> break;
> case FB_EVENT_RESUME:
> + if (!lock_fb_info(info)) {
> + ret = -ENODEV;
> + goto done;
> + }
> fbcon_resumed(info);
> + unlock_fb_info(info);
> break;
> case FB_EVENT_MODE_CHANGE:
> + if (!lock_fb_info(info)) {
> + ret = -ENODEV;
> + goto done;
> + }
> fbcon_modechanged(info);
> + unlock_fb_info(info);
> break;
> case FB_EVENT_MODE_CHANGE_ALL:
> + if (!lock_fb_info(info)) {
> + ret = -ENODEV;
> + goto done;
> + }
> fbcon_set_all_vcs(info);
> + unlock_fb_info(info);
> break;
> case FB_EVENT_MODE_DELETE:
> mode = event->data;
> + if (!lock_fb_info(info)) {
> + ret = -ENODEV;
> + goto done;
> + }
> ret = fbcon_mode_deleted(info, mode);
> + unlock_fb_info(info);
> break;
> case FB_EVENT_FB_UNBIND:
> - ret = fbcon_fb_unbind(info->node);
> + if (!lock_fb_info(info)) {
> + ret = -ENODEV;
> + goto done;
> + }
> + idx = info->node;
> + unlock_fb_info(info);
> + ret = fbcon_fb_unbind(idx);
> break;
> case FB_EVENT_FB_REGISTERED:
> ret = fbcon_fb_registered(info);
> @@ -3178,17 +3217,31 @@ static int fbcon_event_notify(struct notifier_block *self,
> con2fb->framebuffer = con2fb_map[con2fb->console - 1];
> break;
> case FB_EVENT_BLANK:
> + if (!lock_fb_info(info)) {
> + ret = -ENODEV;
> + goto done;
> + }
> fbcon_fb_blanked(info, *(int *)event->data);
> + unlock_fb_info(info);
> break;
> case FB_EVENT_NEW_MODELIST:
> + if (!lock_fb_info(info)) {
> + ret = -ENODEV;
> + goto done;
> + }
> fbcon_new_modelist(info);
> + unlock_fb_info(info);
> break;
> case FB_EVENT_GET_REQ:
> caps = event->data;
> + if (!lock_fb_info(info)) {
> + ret = -ENODEV;
> + goto done;
> + }
> fbcon_get_requirement(info, caps);
> + unlock_fb_info(info);
> break;
> }
> -
> done:
> return ret;
> }
> diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
> index cfd9dce..b64f061 100644
> --- a/drivers/video/fbmem.c
> +++ b/drivers/video/fbmem.c
> @@ -1086,13 +1086,8 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
> return -EINVAL;
> con2fb.framebuffer = -1;
> event.data = &con2fb;
> -
> - if (!lock_fb_info(info))
> - return -ENODEV;
> event.info = info;
> fb_notifier_call_chain(FB_EVENT_GET_CONSOLE_MAP, &event);
> - unlock_fb_info(info);
> -
> ret = copy_to_user(argp, &con2fb, sizeof(con2fb)) ? -EFAULT : 0;
> break;
> case FBIOPUT_CON2FBMAP:
> @@ -1109,12 +1104,8 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
> break;
> }
> event.data = &con2fb;
> - if (!lock_fb_info(info))
> - return -ENODEV;
> event.info = info;
> - ret = fb_notifier_call_chain(FB_EVENT_SET_CONSOLE_MAP,
> - &event);
> - unlock_fb_info(info);
> + ret = fb_notifier_call_chain(FB_EVENT_SET_CONSOLE_MAP, &event);
> break;
> case FBIOBLANK:
> if (!lock_fb_info(info))
--
Everyone knows that debugging is twice as hard as writing a program
in the first place. So if you're as clever as you can be when you write it,
how will you ever debug it? --- Brian Kernighan
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