title: How to interpret kernel panics?
body: <p>I'm new to linux kernel and could barely understand how to debug kernel panics. I have this error below and I don't know where in the C code should I start checking. I was thinking maybe I could echo what functions are being called so I could check where/at what particular function is this null pointer dereferenced. What print function should I use ? How do you interpret the error message below? </p>
  
  <pre><code>Unable to handle kernel NULL pointer dereference at virtual address 0000000d
  pgd = c7bdc000
  [0000000d] *pgd=4785f031, *pte=00000000, *ppte=00000000
  Internal error: Oops: 17 [#1] PREEMPT
  Modules linked in: bcm5892_secdom_fw(P) bcm5892_lcd snd_bcm5892 msr bcm5892_sci bcm589x_ohci_p12 bcm5892_skeypad hx_decoder(P) pinnacle hx_memalloc(P) bcm_udc_dwc scsi_mod g_serial sd_mod usb_storage
  CPU: 0    Tainted: P           (2.6.27.39-WR3.0.2ax_standard #1)
  PC is at __kmalloc+0x70/0xdc
  LR is at __kmalloc+0x48/0xdc
  pc : [c0098cc8]    lr : [c0098ca0]    psr: 20000093
  sp : c7a9fd50  ip : c03a4378  fp : c7a9fd7c
  r10: bf0708b4  r9 : c7a9e000  r8 : 00000040
  r7 : bf06d03c  r6 : 00000020  r5 : a0000093  r4 : 0000000d
  r3 : 00000000  r2 : 00000094  r1 : 00000020  r0 : c03a4378
  Flags: nzCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment user
  Control: 00c5387d  Table: 47bdc008  DAC: 00000015
  Process sh (pid: 1088, stack limit = 0xc7a9e260)
  Stack: (0xc7a9fd50 to 0xc7aa0000)
  fd40:                                     c7a6a1d0 00000020 c7a9fd7c c7ba8fc0
  fd60: 00000040 c7a6a1d0 00000020 c71598c0 c7a9fd9c c7a9fd80 bf06d03c c0098c64
  fd80: c71598c0 00000003 c7a6a1d0 bf06c83c c7a9fdbc c7a9fda0 bf06d098 bf06d008
  fda0: c7159880 00000000 c7a6a2d8 c7159898 c7a9fde4 c7a9fdc0 bf06d130 bf06d078
  fdc0: c79ca000 c7159880 00000000 00000000 c7afbc00 c7a9e000 c7a9fe0c c7a9fde8
  fde0: bf06d4b4 bf06d0f0 00000000 c79fd280 00000000 0f700000 c7a9e000 00000241
  fe00: c7a9fe3c c7a9fe10 c01c37b4 bf06d300 00000000 c7afbc00 00000000 00000000
  fe20: c79cba84 c7463c78 c79fd280 c7473b00 c7a9fe6c c7a9fe40 c00a184c c01c35e4
  fe40: 00000000 c7bb0005 c7a9fe64 c79fd280 c7463c78 00000000 c00a1640 c785e380
  fe60: c7a9fe94 c7a9fe70 c009c438 c00a164c c79fd280 c7a9fed8 c7a9fed8 00000003
  fe80: 00000242 00000000 c7a9feb4 c7a9fe98 c009c614 c009c2a4 00000000 c7a9fed8
  fea0: c7a9fed8 00000000 c7a9ff64 c7a9feb8 c00aa6bc c009c5e8 00000242 000001b6
  fec0: 000001b6 00000241 00000022 00000000 00000000 c7a9fee0 c785e380 c7473b00
  fee0: d8666b0d 00000006 c7bb0005 00000300 00000000 00000000 00000001 40002000
  ff00: c7a9ff70 c79b10a0 c79b10a0 00005402 00000003 c78d69c0 ffffff9c 00000242
  ff20: 000001b6 c79fd280 c7a9ff64 c7a9ff38 c785e380 c7473b00 00000000 00000241
  ff40: 000001b6 ffffff9c 00000003 c7bb0000 c7a9e000 00000000 c7a9ff94 c7a9ff68
  ff60: c009c128 c00aa380 4d18b5f0 08000000 00000000 00071214 0007128c 00071214
  ff80: 00000005 c0027ee4 c7a9ffa4 c7a9ff98 c009c274 c009c0d8 00000000 c7a9ffa8
  ffa0: c0027d40 c009c25c 00071214 0007128c 0007128c 00000241 000001b6 00000000
  ffc0: 00071214 0007128c 00071214 00000005 00073580 00000003 000713e0 400010d0
  ffe0: 00000001 bef0c7b8 000269cc 4d214fec 60000010 0007128c 00000000 00000000
  Backtrace:
  [&lt;c0098c58&gt;] (__kmalloc+0x0/0xdc) from [&lt;bf06d03c&gt;] (gs_alloc_req+0x40/0x70 [g_serial]) r8:c71598c0 r7:00000020 r6:c7a6a1d0 r5:00000040 r4:c7ba8fc0
  [&lt;bf06cffc&gt;] (gs_alloc_req+0x0/0x70 [g_serial]) from [&lt;bf06d098&gt;] (gs_alloc_requests+0x2c/0x78 [g_serial]) r7:bf06c83c r6:c7a6a1d0 r5:00000003 r4:c71598c0
  [&lt;bf06d06c&gt;] (gs_alloc_requests+0x0/0x78 [g_serial]) from [&lt;bf06d130&gt;] (gs_start_io+0x4c/0xac [g_serial]) r7:c7159898 r6:c7a6a2d8 r5:00000000 r4:c7159880
  [&lt;bf06d0e4&gt;] (gs_start_io+0x0/0xac [g_serial]) from [&lt;bf06d4b4&gt;] (gs_open+0x1c0/0x224 [g_serial]) r9:c7a9e000 r8:c7afbc00 r7:00000000 r6:00000000 r5:c7159880 r4:c79ca000
  [&lt;bf06d2f4&gt;] (gs_open+0x0/0x224 [g_serial]) from [&lt;c01c37b4&gt;] (tty_open+0x1dc/0x314)
  [&lt;c01c35d8&gt;] (tty_open+0x0/0x314) from [&lt;c00a184c&gt;] (chrdev_open+0x20c/0x22c)
  [&lt;c00a1640&gt;] (chrdev_open+0x0/0x22c) from [&lt;c009c438&gt;] (__dentry_open+0x1a0/0x2b8) r8:c785e380 r7:c00a1640 r6:00000000 r5:c7463c78 r4:c79fd280
  [&lt;c009c298&gt;] (__dentry_open+0x0/0x2b8) from [&lt;c009c614&gt;] (nameidata_to_filp+0x38/0x50)
  [&lt;c009c5dc&gt;] (nameidata_to_filp+0x0/0x50) from [&lt;c00aa6bc&gt;] (do_filp_open+0x348/0x6f4) r4:00000000
  [&lt;c00aa374&gt;] (do_filp_open+0x0/0x6f4) from [&lt;c009c128&gt;] (do_sys_open+0x5c/0x170)
  [&lt;c009c0cc&gt;] (do_sys_open+0x0/0x170) from [&lt;c009c274&gt;] (sys_open+0x24/0x28) r8:c0027ee4 r7:00000005 r6:00071214 r5:0007128c r4:00071214
  [&lt;c009c250&gt;] (sys_open+0x0/0x28) from [&lt;c0027d40&gt;] (ret_fast_syscall+0x0/0x2c)
  Code: e59c4080 e59c8090 e3540000 159c308c (17943103)
  ---[ end trace be196e7cee3cb1c9 ]---
  note: sh[1088] exited with preempt_count 2
  process '-/bin/sh' (pid 1088) exited. Scheduling for restart.
  
  Welcome to Wind River Linux
  </code></pre>