From 421b40a6286ee343d77d5e51f5ee6d04d7a2a90f Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Fri, 17 May 2013 12:41:03 -0400 Subject: 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 ====================================================== [ 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: [] flush_work+0x5/0x2e0 but task is already holding lock: blocked: (console_lock){+.+.+.}, instance: ffffffff81c2fde0, at: [] vt_ioctl+0xb61/0x1230 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (console_lock){+.+.+.}: [] lock_acquire+0xa4/0x210 [] console_lock+0x77/0x80 [] con_flush_chars+0x2d/0x50 [] n_tty_receive_buf+0x122/0x14d0 [] flush_to_ldisc+0x119/0x170 [] process_one_work+0x211/0x700 [] worker_thread+0x11b/0x3a0 [] kthread+0xed/0x100 [] ret_from_fork+0x7c/0xb0 -> #0 ((&buf->work)){+.+...}: [] __lock_acquire+0x193a/0x1c00 [] lock_acquire+0xa4/0x210 [] flush_work+0x4e/0x2e0 [] __cancel_work_timer+0x95/0x130 [] cancel_work_sync+0x10/0x20 [] tty_port_destroy+0x12/0x20 [] vc_deallocate+0xf8/0x110 [] vt_ioctl+0xb6c/0x1230 [] tty_ioctl+0x285/0xd50 [] do_vfs_ioctl+0x305/0x530 [] sys_ioctl+0x81/0xa0 [] 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: [] vt_ioctl+0xb61/0x1230 stack backtrace: Pid: 26163, comm: (agetty) Not tainted 3.9.0+ #16 Call Trace: [] print_circular_bug+0x200/0x20e [] __lock_acquire+0x193a/0x1c00 [] ? sched_clock+0x9/0x10 [] ? sched_clock+0x9/0x10 [] ? native_sched_clock+0x20/0x80 [] lock_acquire+0xa4/0x210 [] ? flush_work+0x5/0x2e0 [] flush_work+0x4e/0x2e0 [] ? flush_work+0x5/0x2e0 [] ? mark_held_locks+0xbb/0x140 [] ? __free_pages_ok.part.57+0x93/0xc0 [] ? mark_held_locks+0xbb/0x140 [] ? __cancel_work_timer+0x82/0x130 [] __cancel_work_timer+0x95/0x130 [] cancel_work_sync+0x10/0x20 [] tty_port_destroy+0x12/0x20 [] vc_deallocate+0xf8/0x110 [] vt_ioctl+0xb6c/0x1230 [] ? lock_release_holdtime.part.30+0xa1/0x170 [] tty_ioctl+0x285/0xd50 [] ? inode_has_perm.isra.46.constprop.61+0x56/0x80 [] do_vfs_ioctl+0x305/0x530 [] ? selinux_file_ioctl+0x5b/0x110 [] sys_ioctl+0x81/0xa0 [] system_call_fastpath+0x16/0x1b Cc: Dave Jones Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman --- include/linux/vt_kern.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/vt_kern.h b/include/linux/vt_kern.h index e8d65718560..0d33fca4877 100644 --- a/include/linux/vt_kern.h +++ b/include/linux/vt_kern.h @@ -36,7 +36,7 @@ extern int fg_console, last_console, want_console; 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); -- cgit v1.2.3