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Message-ID: <51664e7c.4GhG4Hz0IvwaH1lm%dyoung@redhat.com>
Date: Thu, 11 Apr 2013 13:47:40 +0800
From: dyoung@...hat.com
To: linux-kernel@...r.kernel.org
Subject: cirrusfb: possible circular locking dependency
lockdep is complaining about below, I see it often in kvm guests,
False postive?
[ 600.383445] ======================================================
[ 600.383447] [ INFO: possible circular locking dependency detected ]
[ 600.383452] 3.9.0-rc5+ #71 Not tainted
[ 600.383454] -------------------------------------------------------
[ 600.383458] kworker/0:2/1254 is trying to acquire lock:
[ 600.383475] (&fb_info->lock){+.+.+.}, at: [<ffffffff812e5c92>] lock_fb_info+0x18/0x37
[ 600.383477]
[ 600.383477] but task is already holding lock:
[ 600.383490] (console_lock){+.+.+.}, at: [<ffffffff8135410f>] console_callback+0xb/0xf5
[ 600.383491]
[ 600.383491] which lock already depends on the new lock.
[ 600.383491]
[ 600.383493]
[ 600.383493] the existing dependency chain (in reverse order) is:
[ 600.383499]
[ 600.383499] -> #1 (console_lock){+.+.+.}:
[ 600.383509] [<ffffffff8107e52b>] lock_acquire+0xa3/0x115
[ 600.383516] [<ffffffff8103596a>] console_lock+0x59/0x5b
[ 600.383522] [<ffffffff812e7598>] register_framebuffer+0x20d/0x284
[ 600.383530] [<ffffffff812f69dd>] cirrusfb_pci_register+0x57a/0x617
[ 600.383537] [<ffffffff812d7f2e>] pci_device_probe+0x6b/0xb1
[ 600.383544] [<ffffffff813749d2>] driver_probe_device+0x117/0x2ef
[ 600.383549] [<ffffffff81374bf8>] __driver_attach+0x4e/0x6f
[ 600.383554] [<ffffffff81372e2b>] bus_for_each_dev+0x57/0x89
[ 600.383559] [<ffffffff8137438e>] driver_attach+0x19/0x1b
[ 600.383564] [<ffffffff81374004>] bus_add_driver+0x11d/0x242
[ 600.383569] [<ffffffff813751b7>] driver_register+0x8e/0x114
[ 600.383575] [<ffffffff812d73be>] __pci_register_driver+0x5d/0x62
[ 600.383584] [<ffffffff81a32f0c>] cirrusfb_init+0x52/0xc0
[ 600.383594] [<ffffffff8100026c>] do_one_initcall+0x7a/0x136
[ 600.383600] [<ffffffff81a0ae9b>] kernel_init_freeable+0x141/0x1d0
[ 600.383609] [<ffffffff815aa359>] kernel_init+0x9/0xcc
[ 600.383615] [<ffffffff815cd57c>] ret_from_fork+0x7c/0xb0
[ 600.383621]
[ 600.383621] -> #0 (&fb_info->lock){+.+.+.}:
[ 600.383627] [<ffffffff8107dd25>] __lock_acquire+0xae5/0xe78
[ 600.383632] [<ffffffff8107e52b>] lock_acquire+0xa3/0x115
[ 600.383642] [<ffffffff815c494a>] __mutex_lock_common+0x44/0x32e
[ 600.383648] [<ffffffff815c4cf3>] mutex_lock_nested+0x2a/0x31
[ 600.383653] [<ffffffff812e5c92>] lock_fb_info+0x18/0x37
[ 600.383661] [<ffffffff812ef905>] fbcon_blank+0x168/0x1ee
[ 600.383668] [<ffffffff81351a6d>] do_blank_screen+0x13e/0x1d8
[ 600.383675] [<ffffffff813541cf>] console_callback+0xcb/0xf5
[ 600.383684] [<ffffffff8104cf89>] process_one_work+0x1e8/0x38c
[ 600.383691] [<ffffffff8104d922>] worker_thread+0x130/0x1df
[ 600.383699] [<ffffffff81055144>] kthread+0xac/0xb4
[ 600.383703] [<ffffffff815cd57c>] ret_from_fork+0x7c/0xb0
[ 600.383705]
[ 600.383705] other info that might help us debug this:
[ 600.383705]
[ 600.383707] Possible unsafe locking scenario:
[ 600.383707]
[ 600.383708] CPU0 CPU1
[ 600.383710] ---- ----
[ 600.383713] lock(console_lock);
[ 600.383717] lock(&fb_info->lock);
[ 600.383720] lock(console_lock);
[ 600.383724] lock(&fb_info->lock);
[ 600.383725]
[ 600.383725] *** DEADLOCK ***
[ 600.383725]
[ 600.383728] 3 locks held by kworker/0:2/1254:
[ 600.383739] #0: (events){.+.+.+}, at: [<ffffffff8104cf11>] process_one_work+0x170/0x38c
[ 600.383749] #1: (console_work){+.+...}, at: [<ffffffff8104cf11>] process_one_work+0x170/0x38c
[ 600.383759] #2: (console_lock){+.+.+.}, at: [<ffffffff8135410f>] console_callback+0xb/0xf5
[ 600.383761]
[ 600.383761] stack backtrace:
[ 600.383765] Pid: 1254, comm: kworker/0:2 Not tainted 3.9.0-rc5+ #71
[ 600.383767] Call Trace:
[ 600.383775] [<ffffffff815bddc8>] print_circular_bug+0x1f8/0x209
[ 600.383782] [<ffffffff8107dd25>] __lock_acquire+0xae5/0xe78
[ 600.383788] [<ffffffff812f5e48>] ? cirrusfb_set_blitter+0x169/0x178
[ 600.383794] [<ffffffff8107e52b>] lock_acquire+0xa3/0x115
[ 600.383799] [<ffffffff812e5c92>] ? lock_fb_info+0x18/0x37
[ 600.383807] [<ffffffff815c494a>] __mutex_lock_common+0x44/0x32e
[ 600.383811] [<ffffffff812e5c92>] ? lock_fb_info+0x18/0x37
[ 600.383816] [<ffffffff812e5c92>] ? lock_fb_info+0x18/0x37
[ 600.383823] [<ffffffff812f27d2>] ? bit_clear+0xa7/0xb4
[ 600.383831] [<ffffffff815c4cf3>] mutex_lock_nested+0x2a/0x31
[ 600.383836] [<ffffffff812e5c92>] lock_fb_info+0x18/0x37
[ 600.383842] [<ffffffff812ef905>] fbcon_blank+0x168/0x1ee
[ 600.383848] [<ffffffff815c6ad3>] ? _raw_spin_unlock_irqrestore+0x40/0x4d
[ 600.383855] [<ffffffff8107c3ef>] ? trace_hardirqs_on_caller+0x112/0x1ad
[ 600.383860] [<ffffffff815c6adb>] ? _raw_spin_unlock_irqrestore+0x48/0x4d
[ 600.383868] [<ffffffff810424f5>] ? try_to_del_timer_sync+0x50/0x5c
[ 600.383875] [<ffffffff810425a4>] ? del_timer_sync+0xa3/0xc9
[ 600.383881] [<ffffffff81042501>] ? try_to_del_timer_sync+0x5c/0x5c
[ 600.383887] [<ffffffff81351a6d>] do_blank_screen+0x13e/0x1d8
[ 600.383894] [<ffffffff813541cf>] console_callback+0xcb/0xf5
[ 600.383901] [<ffffffff8104cf89>] process_one_work+0x1e8/0x38c
[ 600.383908] [<ffffffff8104cf11>] ? process_one_work+0x170/0x38c
[ 600.383915] [<ffffffff8104d922>] worker_thread+0x130/0x1df
[ 600.383922] [<ffffffff8104d7f2>] ? manage_workers+0x245/0x245
[ 600.383928] [<ffffffff81055144>] kthread+0xac/0xb4
[ 600.383936] [<ffffffff81055098>] ? __kthread_parkme+0x60/0x60
[ 600.383941] [<ffffffff815cd57c>] ret_from_fork+0x7c/0xb0
[ 600.383948] [<ffffffff81055098>] ? __kthread_parkme+0x60/0x60
--
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