linux-next: boot failures with next-20120411

[Michael Neuling]

Stephen Rothwell <sfr at canb.auug.org.au> wrote:

> Hi all,
> 
> Some (not all) of my PowerPC boot tests have failed like this after
> getting into user mode (this one was just after udev started, but others
> are after other processes getting going):
> 
> Unable to handle kernel paging request for data at address 0xc0000003f9d550
> Faulting instruction address: 0xc0000000001b7f40
> Oops: Kernel access of bad area, sig: 11 [#1]
> SMP NR_CPUS=32 NUMA pSeries
> Modules linked in: ehea
> NIP: c0000000001b7f40 LR: c0000000001b7f14 CTR: c0000000000e04f0
> REGS: c0000003f68bf6b0 TRAP: 0300   Not tainted  (3.4.0-rc2-autokern1)
> MSR: 800000000280b032 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI>  CR: 24422424  XER: 20000001
> SOFTE: 1
> CFAR: 000000000000562c
> DAR: 00c0000003f9d550, DSISR: 40000000
> TASK = c0000003f8818000[3192] 'kdump' THREAD: c0000003f68bc000 CPU: 5
> GPR00: 0000000000000000 c0000003f68bf930 c000000000ce1d40 c0000003fe00ec00 
> GPR04: 00000000000002d0 0000000000000038 c0000003f8f935e8 c000000000e55280 
> GPR08: 0000000000000011 c000000000bcb280 c000000000bcb1e8 000000000028a000 
> GPR12: 0000000024422424 c00000000f33bc80 00000fffdd90a770 0000000000081000 
> GPR16: c0000003f846c000 000000000de4f7a0 f00000000de4f7a0 0000000000000000 
> GPR20: c0000003f8365408 c0000003f8365480 c0000003f8e5d110 0000000000000000 
> GPR24: 0000000000000100 c0000003f8365400 c0000000001e5424 00000000000002d0 
> GPR28: 0000000000000800 00c0000003f9d550 c000000000c5b718 c0000003fe00ec00 
> NIP [c0000000001b7f40] .__kmalloc+0x70/0x230
> LR [c0000000001b7f14] .__kmalloc+0x44/0x230
> Call Trace:
> [c0000003f68bf930] [c0000003f68bf9b0] 0xc0000003f68bf9b0 (unreliable)
> [c0000003f68bf9e0] [c0000000001e5424] .alloc_fdmem+0x24/0x70
> [c0000003f68bfa60] [c0000000001e54f8] .alloc_fdtable+0x88/0x130
> [c0000003f68bfaf0] [c0000000001e5924] .dup_fd+0x384/0x450
> [c0000003f68bfbd0] [c00000000009a310] .copy_process+0x880/0x11d0
> [c0000003f68bfcd0] [c00000000009aee0] .do_fork+0x70/0x400
> [c0000003f68bfdc0] [c0000000000141c4] .sys_clone+0x54/0x70
> [c0000003f68bfe30] [c000000000009aa0] .ppc_clone+0x8/0xc
> Instruction dump:
> 4bff9281 2ba30010 7c7f1b78 40dd00f4 e96d0040 e93f0000 7ce95a14 e9070008 
> 7fa9582a 2fbd0000 41de0054 e81f0022 <7f3d002a> 38000000 886d01f2 980d01f2 
> ---[ end trace 366fe6c7ced3bfb0 ]---
> 
> This did not happen yesterday.  Just wondering if anyone can think of
> anything obvious.  Full console log at
> http://ozlabs.org/~sfr/next-20120411.log.bz2

I managed to bisect this down using pseries_defconfig with next-20120412
to this patch:

  commit 85bbc003b24335e253a392f6a9874103b77abb36
  Author: Jiri Slaby <jslaby at suse.cz>
  Date:   Mon Apr 2 13:54:22 2012 +0200

      TTY: HVC, use tty from tty_port

      The driver already used refcounting. So we just switch it to tty_port
      helpers. And switch to tty_port->lock for tty.

      Signed-off-by: Jiri Slaby <jslaby at suse.cz>
      Cc: linuxppc-dev at lists.ozlabs.org
      Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>

Reverting this commit (and 0146b6939074ebe14ece3604fd00e7be128a3812
otherwise git barfs) fixes the problem on next-20120412.  

I'm assuming we got the ref count changes wrong somewhere in the patch
but the tty code is beyond me.  Jiri, can you take a look?

Mikey