BUG in pty_chars_in_buffer with 2.6.30 git head using ssh

[James Bottomley]

This is a really odd one.  I've used ssh into this box with this same
kernel several times before, I got this (actually logged out as me over
ssh then logged back in as root):

ssh used greatest stack depth: 5340 bytes left
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<c118beb3>] pty_chars_in_buffer+0x13/0x50
*pde = 00000000 
Oops: 0000 [#1] SMP 
last sysfs file: /sys/devices/pci0000:00/0000:00:1c.4/0000:04:00.0/irq
Modules linked in: nfsd exportfs nfs lockd auth_rpcgss sunrpc dm_snapshot dm_mirror dm_region_hash dm_log serio_raw i3000_edac rtc_cmos rtc_core rtc_lib ext3 jbd mbcache sg sr_mod cdrom sd_mod uhci_hcd aic94xx libsas libata usbcore tg3 libphy aic7xxx scsi_transport_spi scsi_transport_sas scsi_mod

Pid: 17335, comm: sshd Tainted: G        W  (2.6.30 #66) IBM eServer 206m-[8485IZZ]-
EIP: 0060:[<c118beb3>] EFLAGS: 00010282 CPU: 0
EIP is at pty_chars_in_buffer+0x13/0x50
EAX: 00000000 EBX: f6da08c8 ECX: f6da08c8 EDX: f61085b0
ESI: 00000000 EDI: f62e4200 EBP: f7a25b0c ESP: f7a25b08
 DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
Process sshd (pid: 17335, ti=f7a24000 task=f5e6e0b0 task.ti=f7a24000)
Stack:
 f6da08c8 f7a25b14 c11890e5 f7a25b2c c1186e77 00a25b2c 00000000 f62e4200
 f6da08c8 f7a25b4c c118318a 00000000 c1186d60 f60897c0 0000000b 00000800
 f62e4200 f7a25e34 c10b810f 000000b2 f7a25bb0 00000000 f7a25bd4 00000020
Call Trace:
 [<c11890e5>] ? tty_chars_in_buffer+0x15/0x20
 [<c1186e77>] ? n_tty_poll+0x117/0x140
 [<c118318a>] ? tty_poll+0x5a/0x70
 [<c1186d60>] ? n_tty_poll+0x0/0x140
 [<c10b810f>] ? do_select+0x32f/0x690
 [<c10b89f0>] ? __pollwait+0x0/0xc0
 [<c10b8ab0>] ? pollwake+0x0/0x50
 [<c10b8ab0>] ? pollwake+0x0/0x50
 [<c10b8ab0>] ? pollwake+0x0/0x50
 [<c10b8ab0>] ? pollwake+0x0/0x50
 [<c10b8ab0>] ? pollwake+0x0/0x50
 [<c10b8ab0>] ? pollwake+0x0/0x50
 [<c1036c3f>] ? lock_timer_base+0x1f/0x40
 [<c127106c>] ? _spin_lock_irqsave+0x2c/0x40
 [<c1036cfd>] ? mod_timer+0x9d/0xd0
 [<c10502fb>] ? trace_hardirqs_on+0xb/0x10
 [<c1036cfd>] ? mod_timer+0x9d/0xd0
 [<c122e245>] ? tcp_event_new_data_sent+0x85/0xc0
 [<c1230ac8>] ? tcp_write_xmit+0x1e8/0xa40
 [<c11e8e76>] ? release_sock+0x26/0xc0
 [<c10502fb>] ? trace_hardirqs_on+0xb/0x10
 [<c1032772>] ? local_bh_enable_ip+0x72/0xc0
 [<c10905df>] ? might_fault+0x3f/0x80
 [<c10905df>] ? might_fault+0x3f/0x80
 [<c109061a>] ? might_fault+0x7a/0x80
 [<c10b8652>] ? core_sys_select+0x1e2/0x330
 [<c10a984c>] ? do_sync_write+0xcc/0x110
 [<c1042550>] ? autoremove_wake_function+0x0/0x40
 [<c10b8957>] ? sys_select+0x27/0xc0
 [<c10aa34b>] ? sys_write+0x3b/0x70
 [<c112bcc8>] ? trace_hardirqs_on_thunk+0xc/0x10
 [<c1002da5>] ? syscall_call+0x7/0xb
Code: 1c 01 00 00 5d c3 66 90 31 c0 5d c3 8d b6 00 00 00 00 8d bf 00 00 00 00 55 89 e5 53 8b 90 20 01 00 00 89 c3 85 d2 74 30 8b 42 54 <8b> 00 8b 48 1c 85 c9 74 24 89 d0 ff d1 89 c2 8b 43 08 66 83 78 
EIP: [<c118beb3>] pty_chars_in_buffer+0x13/0x50 SS:ESP 0068:f7a25b08
CR2: 0000000000000000
---[ end trace 4eaa2a86a8e2da25 ]---

And the machine wedged hard.

ssh had got part way to establishing a connection from the other machine
according to netstat -a.

On reboot, I was able to log in as root perfectly fine.

James



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