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Subjecttty, vt: lockdep warnings
Hi all,

While fuzzing with trinity inside a KVM tools (lkvm) guest running latest -next kernel,
I've stumbled on the following spew:

[ 603.081796] ======================================================
[ 603.081797] [ INFO: possible circular locking dependency detected ]
[ 603.081800] 3.7.0-rc2-next-20121025-sasha-00001-g673f98e-dirty #77 Tainted: G W
[ 603.081801] -------------------------------------------------------
[ 603.081802] kworker/0:1/902 is trying to acquire lock:
[ 603.081815] ((fb_notifier_list).rwsem){.+.+.+}, at: [<ffffffff8114136f>] __blocking_notifier_call_chain+0x7f/0xc0
[ 603.081815]
[ 603.081815] but task is already holding lock:
[ 603.081822] (console_lock){+.+.+.}, at: [<ffffffff81bc833e>] console_callback+0xe/0x130
[ 603.081823]
[ 603.081823] which lock already depends on the new lock.
[ 603.081823]
[ 603.081824]
[ 603.081824] the existing dependency chain (in reverse order) is:
[ 603.081827]
[ 603.081827] -> #1 (console_lock){+.+.+.}:
[ 603.081832] [<ffffffff8118569a>] lock_acquire+0x1aa/0x240
[ 603.081837] [<ffffffff8110b6e8>] console_lock+0x68/0x70
[ 603.081841] [<ffffffff81bc786b>] register_con_driver+0x1b/0x110
[ 603.081844] [<ffffffff81bc7a99>] take_over_console+0x29/0x60
[ 603.081848] [<ffffffff81a6ee33>] fbcon_takeover+0x63/0xc0
[ 603.081851] [<ffffffff81a724af>] fbcon_event_notify+0x33f/0x730
[ 603.081854] [<ffffffff81140e8e>] notifier_call_chain+0xee/0x130
[ 603.081857] [<ffffffff81141388>] __blocking_notifier_call_chain+0x98/0xc0
[ 603.081860] [<ffffffff811413c1>] blocking_notifier_call_chain+0x11/0x20
[ 603.081863] [<ffffffff81a635b6>] fb_notifier_call_chain+0x16/0x20
[ 603.081866] [<ffffffff81a6638d>] register_framebuffer+0x24d/0x290
[ 603.081871] [<ffffffff83961605>] vga16fb_probe+0x1c0/0x227
[ 603.081876] [<ffffffff81e63192>] platform_drv_probe+0x12/0x20
[ 603.081879] [<ffffffff81e61bb5>] driver_probe_device+0x155/0x340
[ 603.081881] [<ffffffff81e61e7e>] __device_attach+0x2e/0x50
[ 603.081884] [<ffffffff81e5fff6>] bus_for_each_drv+0x56/0xa0
[ 603.081887] [<ffffffff81e617a8>] device_attach+0x88/0xc0
[ 603.081889] [<ffffffff81e60236>] bus_probe_device+0x36/0xd0
[ 603.081892] [<ffffffff81e5e0bf>] device_add+0x4df/0x750
[ 603.081895] [<ffffffff81e63aa8>] platform_device_add+0x1e8/0x280
[ 603.081900] [<ffffffff85b11144>] vga16fb_init+0x8d/0xbb
[ 603.081905] [<ffffffff85acecb2>] do_one_initcall+0x7a/0x135
[ 603.081908] [<ffffffff8392eb19>] kernel_init+0x299/0x470
[ 603.081912] [<ffffffff83aedebc>] ret_from_fork+0x7c/0xb0
[ 603.081915]
[ 603.081915] -> #0 ((fb_notifier_list).rwsem){.+.+.+}:
[ 603.081918] [<ffffffff811828df>] __lock_acquire+0x14df/0x1ca0
[ 603.081921] [<ffffffff8118569a>] lock_acquire+0x1aa/0x240
[ 603.081924] [<ffffffff83aea187>] down_read+0x47/0x90
[ 603.081927] [<ffffffff8114136f>] __blocking_notifier_call_chain+0x7f/0xc0
[ 603.081930] [<ffffffff811413c1>] blocking_notifier_call_chain+0x11/0x20
[ 603.081932] [<ffffffff81a635b6>] fb_notifier_call_chain+0x16/0x20
[ 603.081934] [<ffffffff81a65306>] fb_blank+0x36/0xa0
[ 603.081938] [<ffffffff81a729ee>] fbcon_blank+0x14e/0x2d0
[ 603.081941] [<ffffffff81bc7c93>] do_blank_screen+0x1b3/0x2b0
[ 603.081943] [<ffffffff81bc83f3>] console_callback+0xc3/0x130
[ 603.081946] [<ffffffff8112d5a9>] process_one_work+0x3b9/0x770
[ 603.081949] [<ffffffff8112df2a>] worker_thread+0x2ba/0x3f0
[ 603.081951] [<ffffffff81138c33>] kthread+0xe3/0xf0
[ 603.081954] [<ffffffff83aedebc>] ret_from_fork+0x7c/0xb0
[ 603.081955]
[ 603.081955] other info that might help us debug this:
[ 603.081955]
[ 603.081956] Possible unsafe locking scenario:
[ 603.081956]
[ 603.081956] CPU0 CPU1
[ 603.081957] ---- ----
[ 603.081959] lock(console_lock);
[ 603.081961] lock((fb_notifier_list).rwsem);
[ 603.081962] lock(console_lock);
[ 603.081964] lock((fb_notifier_list).rwsem);
[ 603.081964]
[ 603.081964] *** DEADLOCK ***
[ 603.081964]
[ 603.081966] 3 locks held by kworker/0:1/902:
[ 603.081971] #0: (events){.+.+.+}, at: [<ffffffff8112d458>] process_one_work+0x268/0x770
[ 603.081976] #1: (console_work){+.+...}, at: [<ffffffff8112d458>] process_one_work+0x268/0x770
[ 603.081981] #2: (console_lock){+.+.+.}, at: [<ffffffff81bc833e>] console_callback+0xe/0x130
[ 603.081981]
[ 603.081981] stack backtrace:
[ 603.081984] Pid: 902, comm: kworker/0:1 Tainted: G W 3.7.0-rc2-next-20121025-sasha-00001-g673f98e-dirty #77
[ 603.081985] Call Trace:
[ 603.081990] [<ffffffff83a90609>] print_circular_bug+0x1fb/0x20c
[ 603.081994] [<ffffffff811828df>] __lock_acquire+0x14df/0x1ca0
[ 603.081997] [<ffffffff8117cfda>] ? __bfs+0x16a/0x220
[ 603.082000] [<ffffffff8118569a>] lock_acquire+0x1aa/0x240
[ 603.082003] [<ffffffff8114136f>] ? __blocking_notifier_call_chain+0x7f/0xc0
[ 603.082005] [<ffffffff83aea187>] down_read+0x47/0x90
[ 603.082009] [<ffffffff8114136f>] ? __blocking_notifier_call_chain+0x7f/0xc0
[ 603.082011] [<ffffffff8114136f>] __blocking_notifier_call_chain+0x7f/0xc0
[ 603.082014] [<ffffffff811413c1>] blocking_notifier_call_chain+0x11/0x20
[ 603.082017] [<ffffffff81a635b6>] fb_notifier_call_chain+0x16/0x20
[ 603.082019] [<ffffffff81a65306>] fb_blank+0x36/0xa0
[ 603.082022] [<ffffffff81a729ee>] fbcon_blank+0x14e/0x2d0
[ 603.082025] [<ffffffff83aec67d>] ? _raw_spin_unlock_irqrestore+0x5d/0xb0
[ 603.082028] [<ffffffff811802cd>] ? trace_hardirqs_on+0xd/0x10
[ 603.082031] [<ffffffff83aec6a4>] ? _raw_spin_unlock_irqrestore+0x84/0xb0
[ 603.082035] [<ffffffff8111e444>] ? try_to_del_timer_sync+0x64/0x70
[ 603.082037] [<ffffffff8111e548>] ? del_timer_sync+0xf8/0x130
[ 603.082039] [<ffffffff8111e488>] ? del_timer_sync+0x38/0x130
[ 603.082042] [<ffffffff81bc7c93>] do_blank_screen+0x1b3/0x2b0
[ 603.082045] [<ffffffff81bc83f3>] console_callback+0xc3/0x130
[ 603.082048] [<ffffffff8112d5a9>] process_one_work+0x3b9/0x770
[ 603.082050] [<ffffffff8112d458>] ? process_one_work+0x268/0x770
[ 603.082053] [<ffffffff8112ae60>] ? work_fixup_activate+0x90/0x90
[ 603.082056] [<ffffffff81bc8330>] ? poke_blanked_console+0x100/0x100
[ 603.082059] [<ffffffff8112df2a>] worker_thread+0x2ba/0x3f0
[ 603.082061] [<ffffffff8112dc70>] ? rescuer_thread+0x2d0/0x2d0
[ 603.082063] [<ffffffff81138c33>] kthread+0xe3/0xf0
[ 603.082066] [<ffffffff8117d7be>] ? put_lock_stats.isra.16+0xe/0x40
[ 603.082069] [<ffffffff81138b50>] ? insert_kthread_work+0x90/0x90
[ 603.082072] [<ffffffff83aedebc>] ret_from_fork+0x7c/0xb0
[ 603.082074] [<ffffffff81138b50>] ? insert_kthread_work+0x90/0x90

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