Peter Hurley 421b40a628 tty/vt: Fix vc_deallocate() lock order ... Now that the tty port owns the flip buffers and i/o is allowed from the driver even when no tty is attached, the destruction of the tty port (and the flip buffers) must ensure that no outstanding work is pending. Unfortunately, this creates a lock order problem with the console_lock (see attached lockdep report [1] below). For single console deallocation, drop the console_lock prior to port destruction. When multiple console deallocation, defer port destruction until the consoles have been deallocated. tty_port_destroy() is not required if the port has not been used; remove from vc_allocate() failure path. [1] lockdep report from Dave Jones <davej@redhat.com> ====================================================== [ INFO: possible circular locking dependency detected ] 3.9.0+ #16 Not tainted ------------------------------------------------------- (agetty)/26163 is trying to acquire lock: blocked: ((&buf->work)){+.+...}, instance: ffff88011c8b0020, at: [<ffffffff81062065>] flush_work+0x5/0x2e0 but task is already holding lock: blocked: (console_lock){+.+.+.}, instance: ffffffff81c2fde0, at: [<ffffffff813bc201>] vt_ioctl+0xb61/0x1230 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (console_lock){+.+.+.}: [<ffffffff810b3f74>] lock_acquire+0xa4/0x210 [<ffffffff810416c7>] console_lock+0x77/0x80 [<ffffffff813c3dcd>] con_flush_chars+0x2d/0x50 [<ffffffff813b32b2>] n_tty_receive_buf+0x122/0x14d0 [<ffffffff813b7709>] flush_to_ldisc+0x119/0x170 [<ffffffff81064381>] process_one_work+0x211/0x700 [<ffffffff8106498b>] worker_thread+0x11b/0x3a0 [<ffffffff8106ce5d>] kthread+0xed/0x100 [<ffffffff81601cac>] ret_from_fork+0x7c/0xb0 -> #0 ((&buf->work)){+.+...}: [<ffffffff810b349a>] __lock_acquire+0x193a/0x1c00 [<ffffffff810b3f74>] lock_acquire+0xa4/0x210 [<ffffffff810620ae>] flush_work+0x4e/0x2e0 [<ffffffff81065305>] __cancel_work_timer+0x95/0x130 [<ffffffff810653b0>] cancel_work_sync+0x10/0x20 [<ffffffff813b8212>] tty_port_destroy+0x12/0x20 [<ffffffff813c65e8>] vc_deallocate+0xf8/0x110 [<ffffffff813bc20c>] vt_ioctl+0xb6c/0x1230 [<ffffffff813b01a5>] tty_ioctl+0x285/0xd50 [<ffffffff811ba825>] do_vfs_ioctl+0x305/0x530 [<ffffffff811baad1>] sys_ioctl+0x81/0xa0 [<ffffffff81601d59>] system_call_fastpath+0x16/0x1b other info that might help us debug this: [ 6760.076175] Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(console_lock); lock((&buf->work)); lock(console_lock); lock((&buf->work)); *** DEADLOCK *** 1 lock on stack by (agetty)/26163: #0: blocked: (console_lock){+.+.+.}, instance: ffffffff81c2fde0, at: [<ffffffff813bc201>] vt_ioctl+0xb61/0x1230 stack backtrace: Pid: 26163, comm: (agetty) Not tainted 3.9.0+ #16 Call Trace: [<ffffffff815edb14>] print_circular_bug+0x200/0x20e [<ffffffff810b349a>] __lock_acquire+0x193a/0x1c00 [<ffffffff8100a269>] ? sched_clock+0x9/0x10 [<ffffffff8100a269>] ? sched_clock+0x9/0x10 [<ffffffff8100a200>] ? native_sched_clock+0x20/0x80 [<ffffffff810b3f74>] lock_acquire+0xa4/0x210 [<ffffffff81062065>] ? flush_work+0x5/0x2e0 [<ffffffff810620ae>] flush_work+0x4e/0x2e0 [<ffffffff81062065>] ? flush_work+0x5/0x2e0 [<ffffffff810b15db>] ? mark_held_locks+0xbb/0x140 [<ffffffff8113c8a3>] ? __free_pages_ok.part.57+0x93/0xc0 [<ffffffff810b15db>] ? mark_held_locks+0xbb/0x140 [<ffffffff810652f2>] ? __cancel_work_timer+0x82/0x130 [<ffffffff81065305>] __cancel_work_timer+0x95/0x130 [<ffffffff810653b0>] cancel_work_sync+0x10/0x20 [<ffffffff813b8212>] tty_port_destroy+0x12/0x20 [<ffffffff813c65e8>] vc_deallocate+0xf8/0x110 [<ffffffff813bc20c>] vt_ioctl+0xb6c/0x1230 [<ffffffff810aec41>] ? lock_release_holdtime.part.30+0xa1/0x170 [<ffffffff813b01a5>] tty_ioctl+0x285/0xd50 [<ffffffff812b00f6>] ? inode_has_perm.isra.46.constprop.61+0x56/0x80 [<ffffffff811ba825>] do_vfs_ioctl+0x305/0x530 [<ffffffff812b04db>] ? selinux_file_ioctl+0x5b/0x110 [<ffffffff811baad1>] sys_ioctl+0x81/0xa0 [<ffffffff81601d59>] system_call_fastpath+0x16/0x1b Cc: Dave Jones <davej@redhat.com> Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2013-05-20 12:15:59 -07:00
..
.gitignore	TTY: move .gitignore from drivers/char/ to drivers/tty/vt/	2010-11-05 22:18:23 -07:00
consolemap.c	driver: tty: vt: remove cast for kmalloc return value	2013-03-18 17:09:37 -07:00
cp437.uni
defkeymap.c_shipped
defkeymap.map
keyboard.c	TTY: switch tty_schedule_flip	2013-01-15 22:43:15 -08:00
Makefile	tty: vt/Makefile: set the variables to static	2013-01-15 21:52:24 -08:00
selection.c	TTY: vt, fix paste_selection ldisc handling	2012-10-22 16:50:53 -07:00
vc_screen.c	vt: synchronize_rcu() under spinlock is not nice...	2013-03-26 20:30:17 -04:00
vt_ioctl.c	tty/vt: Fix vc_deallocate() lock order	2013-05-20 12:15:59 -07:00
vt.c	tty/vt: Fix vc_deallocate() lock order	2013-05-20 12:15:59 -07:00