Kernel 3.9.6 with lockdep prints following:
[ 600.453133] ===========================
[ 600.453133] [ INFO: possible circular locking dependency detected ]
[ 600.453134] 3.9.6-1-debug-amd64 #1 Tainted: G W O
[ 600.453135] -------------------------------------------------------
[ 600.453135] kworker/0:0/4 is trying to acquire lock:
[ 600.453140] (&fb_info->lock){+.+.+.}, at: [<ffffffff81242e88>] lock_fb_info+0x18/0x37
[ 600.453141]
[ 600.453141] but task is already holding lock:
[ 600.453144] (console_lock){+.+.+.}, at: [<ffffffff812ae160>] console_callback+0xa/0xf3
[ 600.453144]
[ 600.453144] which lock already depends on the new lock.
[ 600.453144]
[ 600.453144]
[ 600.453144] the existing dependency chain (in reverse order) is:
[ 600.453145]
[ 600.453145] -> #1 (console_lock){+.+.+.}:
[ 600.453148] [<ffffffff81092274>] lock_acquire+0x10a/0x15f
[ 600.453150] [<ffffffff81044551>] console_lock+0x69/0x6b
[ 600.453151] [<ffffffff81243c57>] register_framebuffer+0x201/0x278
[ 600.453153] [<ffffffff81af4aea>] efifb_probe+0x408/0x48f
[ 600.453156] [<ffffffff812cd81c>] platform_drv_probe+0x34/0x5e
[ 600.453157] [<ffffffff812cc00d>] driver_probe_device+0x98/0x1b1
[ 600.453159] [<ffffffff812cc174>] __driver_attach+0x4e/0x6f
[ 600.453160] [<ffffffff812ca7bf>] bus_for_each_dev+0x57/0x8a
[ 600.453161] [<ffffffff812cbb2c>] driver_attach+0x19/0x1b
[ 600.453162] [<ffffffff812cb7d0>] bus_add_driver+0xde/0x201
[ 600.453164] [<ffffffff812cc6db>] driver_register+0x8c/0x110
[ 600.453165] [<ffffffff812cd2b1>] platform_driver_register+0x41/0x43
[ 600.453167] [<ffffffff812cd2cb>] platform_driver_probe+0x18/0x8a
[ 600.453168] [<ffffffff81af46c3>] efifb_init+0x276/0x295
[ 600.453170] [<ffffffff810020b4>] do_one_initcall+0x7a/0x136
[ 600.453172] [<ffffffff81ac7ecf>] kernel_init_freeable+0x13f/0x1cc
[ 600.453174] [<ffffffff813de02a>] kernel_init+0x9/0xd6
[ 600.453177] [<ffffffff814005bc>] ret_from_fork+0x7c/0xb0
[ 600.453178]
[ 600.453178] -> #0 (&fb_info->lock){+.+.+.}:
[ 600.453179] [<ffffffff81091a17>] __lock_acquire+0xa64/0xdc0
[ 600.453180] [<ffffffff81092274>] lock_acquire+0x10a/0x15f
[ 600.453182] [<ffffffff813f81b7>] __mutex_lock_common+0x5d/0x371
[ 600.453183] [<ffffffff813f85c6>] mutex_lock_nested+0x3b/0x40
[ 600.453184] [<ffffffff81242e88>] lock_fb_info+0x18/0x37
[ 600.453185] [<ffffffff8124cab2>] fbcon_blank+0x168/0x1ee
[ 600.453187] [<ffffffff812abc46>] do_blank_screen+0x13e/0x1d8
[ 600.453188] [<ffffffff812ae220>] console_callback+0xca/0xf3
[ 600.453190] [<ffffffff8105d4b3>] process_one_work+0x249/0x416
[ 600.453191] [<ffffffff8105dea6>] worker_thread+0x121/0x1ce
[ 600.453193] [<ffffffff81065b2d>] kthread+0xac/0xb4
[ 600.453194] [<ffffffff814005bc>] ret_from_fork+0x7c/0xb0
[ 600.453194]
[ 600.453194] other info that might help us debug this:
[ 600.453194]
[ 600.453195] Possible unsafe locking scenario:
[ 600.453195]
[ 600.453195] CPU0 CPU1
[ 600.453195] ---- ----
[ 600.453196] lock(console_lock);
[ 600.453197] lock(&fb_info->lock);
[ 600.453197] lock(console_lock);
[ 600.453198] lock(&fb_info->lock);
[ 600.453198]
[ 600.453198] *** DEADLOCK ***
[ 600.453198]
[ 600.453199] 3 locks held by kworker/0:0/4:
[ 600.453201] #0: (events){.+.+.+}, at: [<ffffffff8105d3e9>] process_one_work+0x17f/0x416
[ 600.453203] #1: (console_work){+.+...}, at: [<ffffffff8105d3e9>] process_one_work+0x17f/0x416
[ 600.453205] #2: (console_lock){+.+.+.}, at: [<ffffffff812ae160>] console_callback+0xa/0xf3
[ 600.453205]
[ 600.453205] stack backtrace:
[ 600.453206] Pid: 4, comm: kworker/0:0 Tainted: G W O 3.9.6-1-debug-amd64 #1
[ 600.453206] Call Trace:
[ 600.453209] [<ffffffff813f39d3>] print_circular_bug+0x1f6/0x204
[ 600.453211] [<ffffffff81091a17>] __lock_acquire+0xa64/0xdc0
[ 600.453212] [<ffffffff81092274>] lock_acquire+0x10a/0x15f
[ 600.453213] [<ffffffff81242e88>] ? lock_fb_info+0x18/0x37
[ 600.453214] [<ffffffff813f81b7>] __mutex_lock_common+0x5d/0x371
[ 600.453216] [<ffffffff81242e88>] ? lock_fb_info+0x18/0x37
[ 600.453217] [<ffffffff81242e88>] ? lock_fb_info+0x18/0x37
[ 600.453218] [<ffffffff8108f45d>] ? lock_is_held+0x4e/0x5f
[ 600.453219] [<ffffffff813f85c6>] mutex_lock_nested+0x3b/0x40
[ 600.453220] [<ffffffff81242e88>] lock_fb_info+0x18/0x37
[ 600.453221] [<ffffffff8124cab2>] fbcon_blank+0x168/0x1ee
[ 600.453223] [<ffffffff810926d2>] ? trace_hardirqs_on_caller+0x117/0x173
[ 600.453224] [<ffffffff813fa6a5>] ? _raw_spin_unlock_irqrestore+0x48/0x5c
[ 600.453226] [<ffffffff81052285>] ? try_to_del_timer_sync+0x5c/0x67
[ 600.453228] [<ffffffff812abc46>] do_blank_screen+0x13e/0x1d8
[ 600.453229] [<ffffffff812ae220>] console_callback+0xca/0xf3
[ 600.453230] [<ffffffff8105d4b3>] process_one_work+0x249/0x416
[ 600.453231] [<ffffffff8105d3e9>] ? process_one_work+0x17f/0x416
[ 600.453232] [<ffffffff8105dea6>] worker_thread+0x121/0x1ce
[ 600.453233] [<ffffffff8105dd85>] ? manage_workers+0x23c/0x23c
[ 600.453234] [<ffffffff81065b2d>] kthread+0xac/0xb4
[ 600.453235] [<ffffffff81065a81>] ? __kthread_parkme+0x60/0x60
[ 600.453237] [<ffffffff814005bc>] ret_from_fork+0x7c/0xb0
[ 600.453238] [<ffffffff81065a81>] ? __kthread_parkme+0x60/0x60
Feel free to ask me to try a patch or another kernel version.
--
Alexandra N. Kossovsky
OKTET Labs (http://www.oktetlabs.ru/)
e-mail: sasha@oktetlabs.ru