I have already encountered some Oops in my developer's life and whereas I am familiar with some information that I can retrieve from these Oops, there are still pieces of information I can't understand and therefore, can't use to solve problems.
Below you will find an Oops example and I will describe what I can deduce from it. Then, I will ask what the remaining info can teach me about the problem.
[ 716.485951] BUG: unable to handle kernel paging request at fc132158
[ 716.485973] IP: [<fc1936e7>] ubi_change_vtbl_record+0x87/0x1c0 [ubi]
[ 716.485986] *pdpt = 00000000019e6001 *pde = 000000002c558067 *pte = 0000000000000000
[ 716.485997] Oops: 0002 [#1] SMP
[ 716.486004] Modules linked in: ubi(O) mtdchar nandsim nand mtd nand_ids nand_bch bch nand_ecc bnep rfcomm bluetooth parport_pc ppdev lp parport nfsd nfs_acl auth_rpcgss nfs fscache lockd sunrpc binfmt_misc dm_crypt snd_hda_codec_hdmi snd_hda_codec_analog kvm_intel snd_hda_intel snd_hda_codec snd_hwdep kvm snd_pcm snd_seq_midi snd_rawmidi snd_seq_midi_event hid_generic snd_seq cdc_acm snd_timer snd_seq_device mei tpm_tis snd mac_hid serio_raw soundcore lpc_ich snd_page_alloc microcode coretemp usbhid hid nouveau usb_storage ttm drm_kms_helper drm floppy e1000e i2c_algo_bit mxm_wmi video wmi
[ 716.486128] Pid: 3994, comm: ubimkvol Tainted: G O 3.8.0-rc3+ #3 LENOVO 6239AS8/LENOVO
[ 716.486136] EIP: 0060:[<fc1936e7>] EFLAGS: 00010246 CPU: 0
[ 716.486144] EIP is at ubi_change_vtbl_record+0x87/0x1c0 [ubi]
[ 716.486151] EAX: 000000ac EBX: eb5ea000 ECX: 0000002b EDX: 00000000
[ 716.486157] ESI: eb4d1d74 EDI: fc132158 EBP: eb4d1d40 ESP: eb4d1d20
[ 716.486164] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
[ 716.486170] CR0: 8005003b CR2: fc132158 CR3: 27542000 CR4: 000407f0
[ 716.486176] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
[ 716.486183] DR6: ffff0ff0 DR7: 00000400
[ 716.486188] Process ubimkvol (pid: 3994, ti=eb4d0000 task=ec01d9b0 task.ti=eb4d0000)
[ 716.486195] Stack:
[ 716.486199] e755f000 eb4d1d2c c11cad11 eb4d1d34 eb543c00 eb5ea000 00000000 eb4d1e20
[ 716.486215] eb4d1e30 fc195412 e755f000 fc1adf01 eb5ea26c 00000002 0000009e eb5ea480
[ 716.486232] 00000002 e755f22c e755f2ac e755f000 eb4d1d74 2a000000 01000000 00000000
[ 716.486248] Call Trace:
[ 716.486257] [<c11cad11>] ? sysfs_create_file+0x21/0x30
[ 716.486266] [<fc195412>] ubi_create_volume+0x4b2/0x790 [ubi]
[ 716.486277] [<fc19967a>] ubi_cdev_ioctl+0x5da/0xac0 [ubi]
[ 716.486285] [<c117202a>] ? link_path_walk+0x5a/0x7d0
[ 716.486294] [<fc1990a0>] ? vol_cdev_ioctl+0x440/0x440 [ubi]
[ 716.486842] [<c1177e12>] do_vfs_ioctl+0x82/0x5b0
[ 716.487703] [<c1171ced>] ? final_putname+0x1d/0x40
[ 716.488564] [<c1171ced>] ? final_putname+0x1d/0x40
[ 716.489422] [<c1171ced>] ? final_putname+0x1d/0x40
[ 716.489891] [<c1171eb4>] ? putname+0x24/0x40
[ 716.489891] [<c1167239>] ? do_sys_open+0x169/0x1d0
[ 716.489891] [<c11783b0>] sys_ioctl+0x70/0x80
[ 716.489891] [<c16205cd>] sysenter_do_call+0x12/0x38
[ 716.489891] Code: ac 00 00 00 03 bb c8 04 00 00 f7 c7 01 00 00 00 0f 85 ee 00 00 00 f7 c7 02 00 00 00 0f 85 ca 00 00 00 89 c1 31 d2 c1 e9 02 a8 02 <f3> a5 74 0b 0f b7 16 66 89 17 ba 02 00 00 00 a8 01 74 07 0f b6
[ 716.489891] EIP: [<fc1936e7>] ubi_change_vtbl_record+0x87/0x1c0 [ubi] SS:ESP 0068:eb4d1d20
[ 716.489891] CR2: 00000000fc132158
[ 716.516453] ---[ end trace 473b15a7780e19ea ]---
It seems that the kernel wanted to access a wrong page. Now,
- The Oops code 0002 tells me that it occurred while trying to read something in user-mode.
- The Instruction Pointer is at
ubi_change_vtbl_record, which means the offending instruction is located in this function. - I can deduce the path that lead to the faulting function from the
call trace (an ioctl launched from process
ubimkvol)
From there, Is the "stack" a dump of the raw stack of the task ? I can see that some values mentioned are also function addresses found in the call trace. Then, I got fancy looking values like EAX, EBX ... DR7. I think they are CPU registers but still, I don't know what they really are.
Finally, the following line gets me lost :
[ 716.485986] *pdpt = 00000000019e6001 *pde = 000000002c558067 *pte = 0000000000000000
What are pdpt, pde and pte ? I feel they are information about the page fault but I could not retrieve further information after some googling around.
