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fb: reorder the lock sequence to fix potential dead lock
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Following commits:

50e244c fb: rework locking to fix lock ordering on takeover
e93a9a8 fb: Yet another band-aid for fixing lockdep mess
054430e fbcon: fix locking harder

reworked locking to fix related lock ordering on takeover, and introduced console_lock
into fbmem, but it seems that the new lock sequence(fb_info->lock ---> console_lock)
is against with the one in console_callback(console_lock ---> fb_info->lock), and leads to
a potential dead lock as following:

[  601.079000] ======================================================
[  601.079000] [ INFO: possible circular locking dependency detected ]
[  601.079000] 3.11.0 torvalds#189 Not tainted
[  601.079000] -------------------------------------------------------
[  601.079000] kworker/0:3/619 is trying to acquire lock:
[  601.079000]  (&fb_info->lock){+.+.+.}, at: [<ffffffff81397566>] lock_fb_info+0x26/0x60
[  601.079000]
but task is already holding lock:
[  601.079000]  (console_lock){+.+.+.}, at: [<ffffffff8141aae3>] console_callback+0x13/0x160
[  601.079000]
which lock already depends on the new lock.

[  601.079000]
the existing dependency chain (in reverse order) is:
[  601.079000]
-> #1 (console_lock){+.+.+.}:
[  601.079000]        [<ffffffff810dc971>] lock_acquire+0xa1/0x140
[  601.079000]        [<ffffffff810c6267>] console_lock+0x77/0x80
[  601.079000]        [<ffffffff81399448>] register_framebuffer+0x1d8/0x320
[  601.079000]        [<ffffffff81cfb4c8>] efifb_probe+0x408/0x48f
[  601.079000]        [<ffffffff8144a963>] platform_drv_probe+0x43/0x80
[  601.079000]        [<ffffffff8144853b>] driver_probe_device+0x8b/0x390
[  601.079000]        [<ffffffff814488eb>] __driver_attach+0xab/0xb0
[  601.079000]        [<ffffffff814463bd>] bus_for_each_dev+0x5d/0xa0
[  601.079000]        [<ffffffff81447e6e>] driver_attach+0x1e/0x20
[  601.079000]        [<ffffffff81447a07>] bus_add_driver+0x117/0x290
[  601.079000]        [<ffffffff81448fea>] driver_register+0x7a/0x170
[  601.079000]        [<ffffffff8144a10a>] __platform_driver_register+0x4a/0x50
[  601.079000]        [<ffffffff8144a12d>] platform_driver_probe+0x1d/0xb0
[  601.079000]        [<ffffffff81cfb0a1>] efifb_init+0x273/0x292
[  601.079000]        [<ffffffff81002132>] do_one_initcall+0x102/0x1c0
[  601.079000]        [<ffffffff81cb80a6>] kernel_init_freeable+0x15d/0x1ef
[  601.079000]        [<ffffffff8166d2de>] kernel_init+0xe/0xf0
[  601.079000]        [<ffffffff816914ec>] ret_from_fork+0x7c/0xb0
[  601.079000]
-> #0 (&fb_info->lock){+.+.+.}:
[  601.079000]        [<ffffffff810dc1d8>] __lock_acquire+0x1e18/0x1f10
[  601.079000]        [<ffffffff810dc971>] lock_acquire+0xa1/0x140
[  601.079000]        [<ffffffff816835ca>] mutex_lock_nested+0x7a/0x3b0
[  601.079000]        [<ffffffff81397566>] lock_fb_info+0x26/0x60
[  601.079000]        [<ffffffff813a4aeb>] fbcon_blank+0x29b/0x2e0
[  601.079000]        [<ffffffff81418658>] do_blank_screen+0x1d8/0x280
[  601.079000]        [<ffffffff8141ab34>] console_callback+0x64/0x160
[  601.079000]        [<ffffffff8108d855>] process_one_work+0x1f5/0x540
[  601.079000]        [<ffffffff8108e04c>] worker_thread+0x11c/0x370
[  601.079000]        [<ffffffff81095fbd>] kthread+0xed/0x100
[  601.079000]        [<ffffffff816914ec>] ret_from_fork+0x7c/0xb0
[  601.079000]
other info that might help us debug this:

[  601.079000]  Possible unsafe locking scenario:

[  601.079000]        CPU0                    CPU1
[  601.079000]        ----                    ----
[  601.079000]   lock(console_lock);
[  601.079000]                                lock(&fb_info->lock);
[  601.079000]                                lock(console_lock);
[  601.079000]   lock(&fb_info->lock);
[  601.079000]
 *** DEADLOCK ***

so we reorder the lock sequence the same as it in console_callback() to
avoid this issue. And following Tomi's suggestion, fix these similar
issues all in fb subsystem.

Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
(cherry picked from commit fdb31faae11ace02e63e84b39b7840032aa0f1f9)
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@johnweber
Gu Zheng authored and johnweber committed Aug 28, 2014
1 parent d08f50d commit 449b708
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Showing 3 changed files with 51 additions and 28 deletions.
50 changes: 32 additions & 18 deletions drivers/video/fbmem.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1099,14 +1099,16 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
case FBIOPUT_VSCREENINFO:
if (copy_from_user(&var, argp, sizeof(var)))
return -EFAULT;
if (!lock_fb_info(info))
return -ENODEV;
console_lock();
if (!lock_fb_info(info)) {
console_unlock();
return -ENODEV;
}
info->flags |= FBINFO_MISC_USEREVENT;
ret = fb_set_var(info, &var);
info->flags &= ~FBINFO_MISC_USEREVENT;
console_unlock();
unlock_fb_info(info);
console_unlock();
if (!ret && copy_to_user(argp, &var, sizeof(var)))
ret = -EFAULT;
break;
Expand Down Expand Up @@ -1135,12 +1137,14 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
case FBIOPAN_DISPLAY:
if (copy_from_user(&var, argp, sizeof(var)))
return -EFAULT;
if (!lock_fb_info(info))
return -ENODEV;
console_lock();
if (!lock_fb_info(info)) {
console_unlock();
return -ENODEV;
}
ret = fb_pan_display(info, &var);
console_unlock();
unlock_fb_info(info);
console_unlock();
if (ret == 0 && copy_to_user(argp, &var, sizeof(var)))
return -EFAULT;
break;
Expand Down Expand Up @@ -1175,23 +1179,27 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
break;
}
event.data = &con2fb;
if (!lock_fb_info(info))
return -ENODEV;
console_lock();
if (!lock_fb_info(info)) {
console_unlock();
return -ENODEV;
}
event.info = info;
ret = fb_notifier_call_chain(FB_EVENT_SET_CONSOLE_MAP, &event);
console_unlock();
unlock_fb_info(info);
console_unlock();
break;
case FBIOBLANK:
if (!lock_fb_info(info))
return -ENODEV;
console_lock();
if (!lock_fb_info(info)) {
console_unlock();
return -ENODEV;
}
info->flags |= FBINFO_MISC_USEREVENT;
ret = fb_blank(info, arg);
info->flags &= ~FBINFO_MISC_USEREVENT;
console_unlock();
unlock_fb_info(info);
console_unlock();
break;
default:
if (!lock_fb_info(info))
Expand Down Expand Up @@ -1649,12 +1657,15 @@ static int do_register_framebuffer(struct fb_info *fb_info)
registered_fb[i] = fb_info;

event.info = fb_info;
if (!lock_fb_info(fb_info))
return -ENODEV;
console_lock();
if (!lock_fb_info(fb_info)) {
console_unlock();
return -ENODEV;
}

fb_notifier_call_chain(FB_EVENT_FB_REGISTERED, &event);
console_unlock();
unlock_fb_info(fb_info);
console_unlock();
return 0;
}

Expand All @@ -1667,13 +1678,16 @@ static int do_unregister_framebuffer(struct fb_info *fb_info)
if (i < 0 || i >= FB_MAX || registered_fb[i] != fb_info)
return -EINVAL;

if (!lock_fb_info(fb_info))
return -ENODEV;
console_lock();
if (!lock_fb_info(fb_info)) {
console_unlock();
return -ENODEV;
}

event.info = fb_info;
ret = fb_notifier_call_chain(FB_EVENT_FB_UNBIND, &event);
console_unlock();
unlock_fb_info(fb_info);
console_unlock();

if (ret)
return -EINVAL;
Expand Down
19 changes: 13 additions & 6 deletions drivers/video/fbsysfs.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -177,9 +177,12 @@ 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();
if (!lock_fb_info(fb_info)) {
console_unlock();
return -ENODEV;
}

list_splice(&fb_info->modelist, &old_list);
fb_videomode_to_modelist((const struct fb_videomode *)buf, i,
&fb_info->modelist);
Expand All @@ -189,8 +192,8 @@ static ssize_t store_modes(struct device *device,
} else
fb_destroy_modelist(&old_list);

console_unlock();
unlock_fb_info(fb_info);
console_unlock();

return 0;
}
Expand Down Expand Up @@ -404,12 +407,16 @@ static ssize_t store_fbstate(struct device *device,

state = simple_strtoul(buf, &last, 0);

if (!lock_fb_info(fb_info))
return -ENODEV;
console_lock();
if (!lock_fb_info(fb_info)) {
console_unlock();
return -ENODEV;
}

fb_set_suspend(fb_info, (int)state);
console_unlock();

unlock_fb_info(fb_info);
console_unlock();

return count;
}
Expand Down
10 changes: 6 additions & 4 deletions drivers/video/sh_mobile_lcdcfb.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -574,8 +574,9 @@ static int sh_mobile_lcdc_display_notify(struct sh_mobile_lcdc_chan *ch,
switch (event) {
case SH_MOBILE_LCDC_EVENT_DISPLAY_CONNECT:
/* HDMI plug in */
console_lock();
if (lock_fb_info(info)) {
console_lock();


ch->display.width = monspec->max_x * 10;
ch->display.height = monspec->max_y * 10;
Expand All @@ -594,19 +595,20 @@ static int sh_mobile_lcdc_display_notify(struct sh_mobile_lcdc_chan *ch,
fb_set_suspend(info, 0);
}

console_unlock();

unlock_fb_info(info);
}
console_unlock();
break;

case SH_MOBILE_LCDC_EVENT_DISPLAY_DISCONNECT:
/* HDMI disconnect */
console_lock();
if (lock_fb_info(info)) {
console_lock();
fb_set_suspend(info, 1);
console_unlock();
unlock_fb_info(info);
}
console_unlock();
break;

case SH_MOBILE_LCDC_EVENT_DISPLAY_MODE:
Expand Down

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