Hi all,

The IRQ should be disabled somewhere in the path walk, which makes
the GFP_KERNEL allocation in uart_startup() no longer valid..

[    0.499537] kworker/u:1 (29) used greatest stack depth: 7156 bytes left
[    0.500947] ------------[ cut here ]------------
[    0.501445] WARNING: at /c/kernel-tests/src/stable/kernel/lockdep.c:2739 lockdep_trace_alloc+0x86/0xb2()
[    0.502413] Modules linked in:
[    0.502766] Pid: 1, comm: init Not tainted 3.5.0-01258-g1ade992 #182
[    0.503419] Call Trace:
[    0.503696]  [<c10241e8>] warn_slowpath_common+0x48/0x5d
[    0.504250]  [<c10533a0>] ? lockdep_trace_alloc+0x86/0xb2
[    0.504381]  [<c102420c>] warn_slowpath_null+0xf/0x13
[    0.504381]  [<c10533a0>] lockdep_trace_alloc+0x86/0xb2
[    0.504381]  [<c10799aa>] __alloc_pages_nodemask+0x78/0x4f0
[    0.504381]  [<c10505db>] ? trace_hardirqs_off_caller+0x2e/0x88
[    0.504381]  [<c10505db>] ? trace_hardirqs_off_caller+0x2e/0x88
[    0.504381]  [<c1079e31>] __get_free_pages+0xf/0x1f
[    0.504381]  [<c1079e7d>] get_zeroed_page+0xd/0xf
[    0.504381]  [<c10f976f>] uart_startup.part.8+0x46/0x152
[    0.504381]  [<c10f745f>] ? tty_port_tty_set+0x37/0x3c
[    0.504381]  [<c10fa175>] uart_open+0xc9/0x10b
[    0.504381]  [<c10fa0ac>] ? uart_suspend_port+0x229/0x229
[    0.504381]  [<c10f1bc2>] tty_open+0x26b/0x3d3
[    0.504381]  [<c109872a>] chrdev_open+0xf7/0x117
[    0.504381]  [<c10945b7>] do_dentry_open.isra.17+0x148/0x1d2
[    0.504381]  [<c1098633>] ? cdev_put+0x1a/0x1a
[    0.504381]  [<c1094666>] finish_open+0x25/0x31
[    0.504381]  [<c109f955>] do_last.isra.48+0x6d6/0x83a
[    0.504381]  [<c109dcce>] ? __inode_permission+0x4c/0x79
[    0.504381]  [<c109ddd5>] ? link_path_walk+0x97/0x3af
[    0.504381]  [<c109d469>] ? lock_rcu_walk+0x2b/0x61
[    0.504381]  [<c109fb4c>] path_openat+0x93/0x27c
[    0.504381]  [<c109ff3f>] do_filp_open+0x21/0x5d
[    0.504381]  [<c11562d1>] ? _raw_spin_unlock+0x1d/0x20
[    0.504381]  [<c10a8990>] ? alloc_fd+0x12e/0x139
[    0.504381]  [<c1094fb9>] do_sys_open+0x56/0xd2
[    0.504381]  [<c1095050>] sys_open+0x1b/0x20
[    0.504381]  [<c11564bd>] syscall_call+0x7/0xb

Thanks,
Fengguang