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SubjectRe: Linux 3.3-rc4
On Fri, 24 Feb 2012, Jiri Kosina wrote:

> Running DEBUG_SLAB kernel since I have first hit the bug, but nothing
> popped up yet. Seems undebuggable so far.
> On the other hand I wouldn't blame HW for a bit-flip, as it was a clear
> NULL pointer (plus 0x30 offset), not a random garbage.

Hmm, just got this as a result of lsmod (topmost commit g586c6e7)

BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
IP: [<ffffffff810a6380>] m_show+0x70/0x190
PGD 77c60067 PUD 3756c067 PMD 0
Oops: 0000 [#1] SMP
Modules linked in: af_packet rfcomm bnep tun iptable_mangle xt_DSCP nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables xt
nf_conntrack iptable_filter ip_tables x_tables cpufreq_conservative cpufreq_userspace cpufreq_powersave acpi_cpufreq mperf microc
btusb bluetooth i2c_i801 iTCO_wdt snd_hda_codec_conexant e1000e pcspkr iTCO_vendor_support cfg80211 snd_hda_intel snd_hda_codec s
d_acpi rfkill battery snd ac soundcore tpm_tis wmi tpm tpm_bios autofs4 uhci_hcd i915 drm_kms_helper ehci_hcd drm i2c_algo_bit usb
a_generic thermal thermal_sys

Pid: 3960, comm: lsmod Not tainted 3.3.0-rc5-00088-g586c6e7 #10 LENOVO 7470BN2/7470BN2
RIP: 0010:[<ffffffff810a6380>] [<ffffffff810a6380>] m_show+0x70/0x190
RSP: 0018:ffff880037b8fe08 EFLAGS: 00010203
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000001
RDX: 0000000000000000 RSI: 0000000000001000 RDI: ffff8800379b332c
RBP: ffff880037b8fe48 R08: 0000000000000020 R09: 000000000000ffff
R10: 0000000000000001 R11: 0000ffffffff6c0a R12: ffffffffa0175490
R13: ffff880036c44d80 R14: ffffffffa0175280 R15: ffffffffa0175288
FS: 00007f78f52a0700(0000) GS:ffff88007c200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000020 CR3: 000000007563a000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process lsmod (pid: 3960, threadinfo ffff880037b8e000, task ffff880073624040)
ffff880037b8fe28 ffffffff814fa56e ffff880037b8fe88 ffffffffa0175288
ffff880036c44d80 0000000000000320 ffff880037b8fe80 000000000000002b
ffff880037b8feb8 ffffffff8118dda7 ffff880037b8ff48 00000000000003d5
Call Trace:
[<ffffffff814fa56e>] ? mutex_lock_nested+0x3e/0x50
[<ffffffff8118dda7>] seq_read+0x287/0x400
[<ffffffff8118db20>] ? seq_lseek+0x110/0x110
[<ffffffff811cea6d>] proc_reg_read+0x7d/0xc0
[<ffffffff8116b258>] vfs_read+0xc8/0x130
[<ffffffff8116b3b0>] sys_read+0x50/0x90
[<ffffffff81505779>] system_call_fastpath+0x16/0x1b
Code: e8 06 ff ff ff 48 c7 c6 c6 50 79 81 48 89 c2 4c 89 ef 31 c0 e8 12 76 0e 00 49 8b 9e 10 02 00 00 31 c0 4c 39 e3 74 2a 0f 1f 4
89 ef 48 83 c2 18 e8
RIP [<ffffffff810a6380>] m_show+0x70/0x190
RSP <ffff880037b8fe08>
CR2: 0000000000000020

So again NULL+offset, again a vfs-related structure, but a completely
different codepath.

This particular kernel didn't have DEBUG_SLAB turned on, unfortunately.

Jiri Kosina

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