From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King Date: Wed, 30 Jan 2013 21:52:11 +0000 Subject: Re: BUG: circular locking dependency detected Message-Id: <20130130215211.GA28418@flint.arm.linux.org.uk> List-Id: References: <20130130200648.GA13298@flint.arm.linux.org.uk> In-Reply-To: <20130130200648.GA13298@flint.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Florian Tobias Schandinat , linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Daniel Vetter , Greg Kroah-Hartman Also adding Greg and Daniel to this as Daniel introduced the lockdep checking. This looks extremely horrid to be to solve - the paths are rather deep where the dependency occurs. The two paths between the locks are: console_lock+0x5c/0x70 register_con_driver+0x44/0x150 take_over_console+0x24/0x3b4 fbcon_takeover+0x70/0xd4 fbcon_event_notify+0x7c8/0x818 notifier_call_chain+0x4c/0x8c __blocking_notifier_call_chain+0x50/0x68 blocking_notifier_call_chain+0x20/0x28 and __blocking_notifier_call_chain+0x34/0x68 blocking_notifier_call_chain+0x20/0x28 fb_notifier_call_chain+0x20/0x28 fb_blank+0x40/0xac fbcon_blank+0x1f4/0x29c do_blank_screen+0x1b8/0x270 console_callback+0x74/0x138 On Wed, Jan 30, 2013 at 08:06:48PM +0000, Russell King wrote: > This looks like a bug in the framebuffer/console layers. Looks like > we have one path where we call the notifier list, and a called > function takes the console lock, and another path where we hold the > console lock while calling the notifier list. > > =========================== > [ INFO: possible circular locking dependency detected ] > 3.8.0-rc4+ #656 Not tainted > ------------------------------------------------------- > kworker/0:1/442 is trying to acquire lock: > ((fb_notifier_list).rwsem){.+.+.+}, at: [] __blocking_notifier_call_chain+0x34/0x68 > > but task is already holding lock: > (console_lock){+.+.+.}, at: [] console_callback+0x14/0x138 > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #1 (console_lock){+.+.+.}: > [] __lock_acquire+0x1d20/0x1e80 > [] lock_acquire+0x68/0x7c > [] console_lock+0x5c/0x70 > [] register_con_driver+0x44/0x150 > [] take_over_console+0x24/0x3b4 > [] fbcon_takeover+0x70/0xd4 > [] fbcon_event_notify+0x7c8/0x818 > [] notifier_call_chain+0x4c/0x8c > [] __blocking_notifier_call_chain+0x50/0x68 > [] blocking_notifier_call_chain+0x20/0x28 > [] fb_notifier_call_chain+0x20/0x28 > [] register_framebuffer+0x18c/0x238 > [] clcdfb_probe+0x2b0/0x3c0 > [] amba_probe+0x88/0xa0 > [] driver_probe_device+0x84/0x218 > [] __driver_attach+0x9c/0xa0 > [] bus_for_each_dev+0x5c/0x88 > [] driver_attach+0x20/0x28 > [] bus_add_driver+0xa4/0x244 > [] driver_register+0x80/0x14c > [] amba_driver_register+0x48/0x5c > [] amba_clcdfb_init+0x28/0x3c > [] do_one_initcall+0x44/0x1ac > [] kernel_init_freeable+0x104/0x1c8 > [] kernel_init+0x10/0xec > [] ret_from_fork+0x14/0x24 > > -> #0 ((fb_notifier_list).rwsem){.+.+.+}: > [] print_circular_bug+0x84/0x2f0 > [] __lock_acquire+0x1e0c/0x1e80 > [] lock_acquire+0x68/0x7c > [] down_read+0x34/0x44 > [] __blocking_notifier_call_chain+0x34/0x68 > [] blocking_notifier_call_chain+0x20/0x28 > [] fb_notifier_call_chain+0x20/0x28 > [] fb_blank+0x40/0xac > [] fbcon_blank+0x1f4/0x29c > [] do_blank_screen+0x1b8/0x270 > [] console_callback+0x74/0x138 > [] process_one_work+0x1b4/0x4ec > [] worker_thread+0x17c/0x4bc > [] kthread+0xb0/0xbc > [] ret_from_fork+0x14/0x24 > > other info that might help us debug this: > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(console_lock); > lock((fb_notifier_list).rwsem); > lock(console_lock); > lock((fb_notifier_list).rwsem); > > *** DEADLOCK *** > > 3 locks held by kworker/0:1/442: > #0: (events){.+.+..}, at: [] process_one_work+0x140/0x4ec > #1: (console_work){+.+...}, at: [] process_one_work+0x140/0x4ec > #2: (console_lock){+.+.+.}, at: [] console_callback+0x14/0x138 > > stack backtrace: > Backtrace: > [] (dump_backtrace+0x0/0x10c) from [] (dump_stack+0x18/0x1c) > r6:c05323f0 r5:c0524800 r4:c05323f0 r3:cf8f6b80 > [] (dump_stack+0x0/0x1c) from [] (print_circular_bug+0x1e4/0x2f0) > [] (print_circular_bug+0x0/0x2f0) from [] (__lock_acquire+0x1e0c/0x1e80) > [] (__lock_acquire+0x0/0x1e80) from [] (lock_acquire+0x68/0x7c) > [] (lock_acquire+0x0/0x7c) from [] (down_read+0x34/0x44) > r7:00000010 r6:cfb7dd20 r5:00000002 r4:c04715cc > [] (down_read+0x0/0x44) from [] (__blocking_notifier_call_chain+0x34/0x68) > r5:ffffffff r4:c04715cc > [] (__blocking_notifier_call_chain+0x0/0x68) from [] (blocking_notifier_call_chain+0x20/0x28) > r7:cf0ffc00 r6:00000001 r5:cfb7dd20 r4:cfb5f800 > [] (blocking_notifier_call_chain+0x0/0x28) from [] (fb_notifier_call_chain+0x20/0x28) > [] (fb_notifier_call_chain+0x0/0x28) from [] (fb_blank+0x40/0xac) > [] (fb_blank+0x0/0xac) from [] (fbcon_blank+0x1f4/0x29c) > r6:00000001 r5:cf80a000 r4:cfb5f800 > [] (fbcon_blank+0x0/0x29c) from [] (do_blank_screen+0x1b8/0x270) > [] (do_blank_screen+0x0/0x270) from [] (console_callback+0x74/0x138) > r7:c0ba8640 r6:c0bac300 r5:c099a51c r4:c099a51c > [] (console_callback+0x0/0x138) from [] (process_one_work+0x1b4/0x4ec) > r6:c0bac300 r5:cf9489c0 r4:c0472e3c r3:c01c2b34 > [] (process_one_work+0x0/0x4ec) from [] (worker_thread+0x17c/0x4bc) > [] (worker_thread+0x0/0x4bc) from [] (kthread+0xb0/0xbc) > [] (kthread+0x0/0xbc) from [] (ret_from_fork+0x14/0x24) > r8:00000000 r7:00000000 r6:00000000 r5:c004886c r4:cf84dde8 > > -- > Russell King > Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ > maintainer of: -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: