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>
diff --git a/include/linux/vt_kern.h b/include/linux/vt_kern.h
index e8d6571..0d33fca 100644
--- a/include/linux/vt_kern.h
+++ b/include/linux/vt_kern.h
@@ -36,7 +36,7 @@
int vc_allocate(unsigned int console);
int vc_cons_allocated(unsigned int console);
int vc_resize(struct vc_data *vc, unsigned int cols, unsigned int lines);
-void vc_deallocate(unsigned int console);
+struct vc_data *vc_deallocate(unsigned int console);
void reset_palette(struct vc_data *vc);
void do_blank_screen(int entering_gfx);
void do_unblank_screen(int leaving_gfx);