Re: BUG on 2.6.20-rc1 when using gdb

[Jeremy Fitzhardinge <jeremy@goop.org>]

Andrew Morton wrote:
> On Sun, 17 Dec 2006 20:55:18 -0500
> "Andrew J. Barr" <andrew.james.barr@gmail.com> wrote:
>
>   
>> When I was using gdb to debug xchat-gnome, I got a kernel BUG and stack
>> trace as the program was running (e.g. I had typed 'run' in gdb):
>>
>> WARNING at kernel/softirq.c:137 local_bh_enable()
>>  [<c0103cd6>] dump_trace+0x68/0x1d9
>>  [<c0103e5f>] show_trace_log_lvl+0x18/0x2c
>>  [<c01044d3>] show_trace+0xf/0x11
>>  [<c010455e>] dump_stack+0x12/0x14
>>  [<c011cc7d>] local_bh_enable+0x44/0x94
>>  [<c02871b9>] unix_release_sock+0x6e/0x1fe
>>  [<c02887eb>] unix_stream_connect+0x3b4/0x3cf
>>  [<c0232dee>] sys_connect+0x82/0xad
>>  [<c0233641>] sys_socketcall+0xac/0x261
>>  [<c0102d38>] syscall_call+0x7/0xb
>>  [<b7f70822>] 0xb7f70822
>>  =======================
>> ------------[ cut here ]------------
>> kernel BUG at fs/buffer.c:1235!
>> invalid opcode: 0000 [#1]
>> PREEMPT
>> Modules linked in: binfmt_misc rfcomm l2cap i915 drm bluetooth nfs nfsd
>> exportfs lockd nfs_acl sunrpc nvram uinput ipv6 ppdev lp button ac
>> battery dm_crypt dm_snapshot dm_mirror dm_mod fuse cpufreq_conservative
>> cpufreq_ondemand cpufreq_performance cpufreq_powersave
>> speedstep_centrino freq_table ibm_acpi loop snd_intel8x0m snd_pcm_oss
>> snd_mixer_oss snd_intel8x0 snd_ac97_codec pcmcia ac97_bus irtty_sir
>> sir_dev ipw2200 snd_pcm snd_timer irda ieee80211 ieee80211_crypt
>> crc_ccitt rtc parport_pc parport 8250_pnp snd soundcore 8250_pci 8250
>> serial_core firmware_class i2c_i801 yenta_socket rsrc_nonstatic
>> pcmcia_core snd_page_alloc i2c_core intel_agp agpgart evdev tsdev joydev
>> ext3 jbd mbcache ide_cd cdrom ide_disk ide_generic e100 mii generic piix
>> ide_core ehci_hcd uhci_hcd usbcore
>> CPU:    0
>> EIP:    0060:[<c0179266>]    Not tainted VLI
>> EFLAGS: 00010046   (2.6.20-rc1 #1)
>> EIP is at __find_get_block+0x1c/0x16f
>> eax: 00000086   ebx: 00000000   ecx: 00000000   edx: 0088a800
>> esi: 0088a800   edi: 00000000   ebp: dfffd040   esp: cad2dd30
>> ds: 007b   es: 007b   ss: 0068
>> Process xchat-gnome (pid: 4322, ti=cad2c000 task=d0cd3ab0
>> task.ti=cad2c000)
>> Stack: cad2dd58 c02caa0b 00000002 0000000e 0000000b 00000001 e8836580
>> 0088a800
>>        00000000 00000000 e8836610 00000000 c01793dc 00001000 c03ab3e0
>> f3cadd80
>>        00000086 c90d41b0 0088a800 00000000 dfffd040 00008000 00000000
>> 00000002
>> Call Trace:
>>  [<c01793dc>] __getblk+0x23/0x268
>>  [<f040d4c6>] ext3_getblk+0x10b/0x244 [ext3]
>>  [<f040e364>] ext3_bread+0x19/0x70 [ext3]
>>  [<f04106f3>] dx_probe+0x43/0x2c9 [ext3]
>>  [<f04119b3>] ext3_htree_fill_tree+0x99/0x1ba [ext3]
>>  [<f040ab77>] ext3_readdir+0x1d4/0x5ed [ext3]
>>  [<c0167b29>] vfs_readdir+0x63/0x8d
>>  [<c0167bb6>] sys_getdents64+0x63/0xa5
>>  [<c0102d38>] syscall_call+0x7/0xb
>>  [<b7f70822>] 0xb7f70822
>>  =======================
>> Code: 8b 40 08 a8 08 74 05 e8 02 2f 11 00 5b 5e c3 55 89 c5 57 89 cf 56
>> 89 d6 53 83 ec 20 9c 58 90 8d b4 26 00 00 00 00 f6 c4 02 75 04 <0f> 0b
>> eb fe 89 e0 25 00 e0 ff ff ff 40 14 31 c9 8b 1c 8d a0 74
>> EIP: [<c0179266>] __find_get_block+0x1c/0x16f SS:ESP 0068:cad2dd30
>>
>> This happens on 2.6.20-rc1 but not 2.6.19.
>>
>>     
>
> And it's repeatable, yes?
>
> And you're sure that use of gdb triggers it?
>
> Something is forgetting to reenable local interrupts.

"walt" <w41ter@gmail.com> reported a similar problem which he bisected
down to the PDA changeset which touches ptrace
(66e10a44d724f1464b5e8b5a3eae1e2cbbc2cca6).  I haven't managed to repo
the problem, but I guess there's something nasty going on in ptrace -
maybe its screwing up eflags on the stack or something.  Need to
double-check all the conversions from kernel<->usermode registers.  Hm,
wonder if its fixed with the %gs->%fs conversion patch applied?

    J
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