[crash] NULL pointer dereference at IP: [<ffffffff812e9ccb>]uart_close+0x2a/0x1e4

[Ingo Molnar]

here's a new crash i havent seen before:

modprobe used greatest stack depth: 3416 bytes left
BUG: unable to handle kernel NULL pointer dereference at 0000000000000240
IP: [<ffffffff812e9ccb>] uart_close+0x2a/0x1e4
PGD 774b8067 PUD 774b6067 PMD 0 
Oops: 0000 [#1] DEBUG_PAGEALLOC
last sysfs file: 
CPU 0 
Modules linked in:
Pid: 1107, comm: hwclock Not tainted 2.6.32-rc3-tip #8181 System Product Name
RIP: 0010:[<ffffffff812e9ccb>]  [<ffffffff812e9ccb>] uart_close+0x2a/0x1e4
RSP: 0018:ffff88007754fb88  EFLAGS: 00010246
RAX: ffffffff812e9ca1 RBX: ffff8800774bcc80 RCX: 0000000000000000
RDX: ffff88007b320900 RSI: ffff8800774bcc80 RDI: ffff88007b3bb000
RBP: ffff88007754fbb8 R08: ffff88007754fab8 R09: ffffffff8103f397
R10: 0000000000000246 R11: ffffffff812c1981 R12: 0000000000000000
R13: 0000000000000000 R14: ffff88007b3bb000 R15: 0000000000000000
FS:  00007f7a51c4c6f0(0000) GS:ffffffff81b38000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000000240 CR3: 00000000774c2000 CR4: 00000000000026f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process hwclock (pid: 1107, threadinfo ffff88007754e000, task ffff88007a4e8000)
Stack:
 ffff88007754fbb8 ffff88007b3bb000 0000000000000000 00000000fffffffa
<0> 0000000000000000 0000000000000000 ffff88007754fc98 ffffffff812c3976
<0> ffff88007754fbf8 0000000000000246 ffff88007b338150 ffff88007b338000
Call Trace:
 [<ffffffff812c3976>] tty_release_dev+0x1ca/0x4d8
 [<ffffffff817718fe>] ? mutex_unlock+0xe/0x10
 [<ffffffff81773725>] ? _spin_unlock+0x2b/0x2f
 [<ffffffff812c4235>] tty_open+0x33f/0x41d
 [<ffffffff81117245>] chrdev_open+0x179/0x19a
 [<ffffffff8111285a>] __dentry_open+0x1cf/0x2f9
 [<ffffffff811170cc>] ? chrdev_open+0x0/0x19a
 [<ffffffff811137e4>] nameidata_to_filp+0x45/0x56
 [<ffffffff811200fa>] do_filp_open+0x58a/0xa39
 [<ffffffff81094f37>] ? __lock_acquire+0x8f5/0x95a
 [<ffffffff8103f3d6>] ? native_sched_clock+0x3b/0x52
 [<ffffffff811294b8>] ? alloc_fd+0x110/0x11f
 [<ffffffff81773725>] ? _spin_unlock+0x2b/0x2f
 [<ffffffff811294b8>] ? alloc_fd+0x110/0x11f
 [<ffffffff81112598>] do_sys_open+0x62/0x109
 [<ffffffff81112672>] sys_open+0x20/0x22
 [<ffffffff81038dff>] system_call_fastpath+0x16/0x1b
Code: c3 55 48 89 e5 41 57 41 56 41 55 41 54 53 48 83 ec 08 0f 1f 44 00 00 f6 05 9d 2e 55 01 08 4c 8b af 28 04 00 00 49 89 fe 48 89 f3 <4d> 8b bd 40 02 00 00 74 16 f6 05 87 2e 55 01 40 74 0d 80 3d 33 
RIP  [<ffffffff812e9ccb>] uart_close+0x2a/0x1e4
 RSP <ffff88007754fb88>
CR2: 0000000000000240
---[ end trace 16e4ef47b9d6effc ]---
sky2 eth0: enabling interface

Note, i have your fix below applied in tip:out-of-tree - it might be the 
source of this bug? (If yes then this isnt an .32-rc4 problem.)

	Ingo

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