Date:	Thu, 25 Sep 2008 20:05:23 +0530
From:	Tej <bewith.tej@...il.com>
To:	"Jason Wessel" <jason.wessel@...driver.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Kernel PANIC with 2.6.27-rc6

On 9/11/08, Jason Wessel <jason.wessel@...driver.com> wrote:
> Tej wrote:
>> observed a panic on 2.6.27-rc6 caused by  enabling
>> "CONFIG_KGDB_TESTS_ON_BOOT" option
>>
>> panic logged using serial console and .config are attached.
>>
>> Linux version 2.6.27-rc6 (root@...er-desktop) (gcc version 4.2.3
> (Ubuntu 4.2.3-8
> [clip]
>> kgdb: Registered I/O driver kgdbts.
>> kgdbts:RUN plant and detach test
>> kgdbts:RUN sw breakpoint test
>> kgdbts:RUN bad memory access test
>> kgdbts:RUN singlestep test 1000 iterations
>> kgdbts:RUN singlestep [0/1000]
>> kgdbts:RUN singlestep [100/1000]
>> kgdbts: BP mismatch c0109c02 expected c02ad250
>
>
>
> So if we break this down into what it means, the kgdb test got an
> exception and stopped somewhere other than where it placed the
> breakpoint.  In this case 0xc0109c02 which you can see right after the
> text "BP mismatch".

i have obsvered this  bug from 2.6.27-rc1 to rc7
however the 2.6.26 was fine


>
> This address is in your stack trace below (read on)

>
>
>> ------------[ cut here ]------------
>> WARNING: at drivers/misc/kgdbts.c:302 check_and_rewind_pc+0xb2/0xe0()
>> Modules linked in:
>> Pid: 0, comm: swapper Not tainted 2.6.27-rc6 #16
>>  [<c0125d04>] warn_on_slowpath+0x54/0x70
>>  [<c01260f0>] ? __call_console_drivers+0x60/0x70
>>  [<c013c15b>] ? up+0x2b/0x40
>>  [<c0126634>] ? release_console_sem+0x1a4/0x1c0
>>  [<c01548f7>] ? __rmqueue_smallest+0xb7/0x130
>>  [<c02445e7>] ? __copy_to_user_ll+0x57/0x60
>>  [<c0153dc0>] ? probe_kernel_write+0x20/0x40
>>  [<c02ad250>] ? kgdbts_break_test+0x0/0x30
>>  [<c0126bab>] ? printk+0x1b/0x20
>>  [<c02ad250>] ? kgdbts_break_test+0x0/0x30
>>  [<c02adfb2>] check_and_rewind_pc+0xb2/0xe0
>>  [<c0109c02>] ? mwait_idle+0x32/0x40
>
>
> So if you were to do:
> gdb ./vmlinux
> i line *0xc0109c02
>
> It will print the line of source that caused the problem.  It is
> probably the case that this is a victim however, as this looks like
> some kind of nmi race condition.
>
> Perhaps you could confirm this?

ok so i did git bisection which pointed:-

commit 3ed3f06295e69700fa808396f7b350bff2b69de0
Author: Cyrill Gorcunov <gorcunov@...il.com>
Date:   Wed Jun 4 01:00:47 2008 +0400

    x86: nmi - consolidate nmi_watchdog_default for 32bit mode

    64bit mode bootstrap code does set nmi_watchdog to NMI_NONE
    by default and doing the same on 32bit mode is safe too.
    Such an action saves us from several #ifdef.



git -bisection log.

git-bisect start
# bad: [6e86841d05f371b5b9b86ce76c02aaee83352298] Linux 2.6.27-rc1
git-bisect bad 6e86841d05f371b5b9b86ce76c02aaee83352298
# good: [bce7f793daec3e65ec5c5705d2457b81fe7b5725] Linux 2.6.26
git-bisect good bce7f793daec3e65ec5c5705d2457b81fe7b5725
# bad: [d20b27478d6ccf7c4c8de4f09db2bdbaec82a6c0] V4L/DVB (8415):
gspca: Infinite loop in i2c_w() of etoms.
git-bisect bad d20b27478d6ccf7c4c8de4f09db2bdbaec82a6c0
# bad: [666484f0250db2e016948d63b3ef33e202e3b8d0] Merge branch
'core/softirq' of
git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
git-bisect bad 666484f0250db2e016948d63b3ef33e202e3b8d0
# bad: [d59fdcf2ac501de99c3dfb452af5e254d4342886] Merge commit
'v2.6.26' into x86/core
git-bisect bad d59fdcf2ac501de99c3dfb452af5e254d4342886
# good: [3de352bbd86f890dd0c5e1c09a6a1b0b29e0f8ce] Merge branch
'x86/mpparse' into x86/devel
git-bisect good 3de352bbd86f890dd0c5e1c09a6a1b0b29e0f8ce
# bad: [b4df32f4aeef8794d0135fc8dc250acb44cfee60] x86: fix warning in
e820_reserve_resources with 32bit
git-bisect bad b4df32f4aeef8794d0135fc8dc250acb44cfee60
# bad: [7f0be02c5ed1deb04c54c6a17f412e04f417df11] x86: move
boot_params declaring to setup.c
git-bisect bad 7f0be02c5ed1deb04c54c6a17f412e04f417df11
# bad: [4b62ac9a2b859f932afd5625362c927111b7dd9b] Merge branch
'x86/nmi' into x86/devel
git-bisect bad 4b62ac9a2b859f932afd5625362c927111b7dd9b
# bad: [f781b03c4b1c713ac000877c8bbc31fc4164a29b] x86:
touch_nmi_watchdog(): reset alert counters for supported nmi_watchdog
modes only
git-bisect bad f781b03c4b1c713ac000877c8bbc31fc4164a29b
# good: [96f9dcb10755e96eae706b9e869c0dc25adb3d74] x86: nmi_64.c - use
for_each_possible_cpu helper
git-bisect good 96f9dcb10755e96eae706b9e869c0dc25adb3d74
# good: [ba3a5974239293d921235e6fa82b09b670e674ef] - fix typo in
include/asm-x86/nmi.h
git-bisect good ba3a5974239293d921235e6fa82b09b670e674ef
# bad: [3ed3f06295e69700fa808396f7b350bff2b69de0] x86: nmi -
consolidate nmi_watchdog_default for 32bit mode
git-bisect bad 3ed3f06295e69700fa808396f7b350bff2b69de0
# good: [3d1ba1da2b4ff4ace7801e99fb9a3095b182d847] x86: fix nmi.c build bug
git-bisect good 3d1ba1da2b4ff4ace7801e99fb9a3095b182d847


One more point, this bug i have observed on intel VT machine, on
non-VT machine i couldn't able to trigger this bug.

cat /proc/cpuinfo | grep vmx

flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm
constant_tsc pni monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr
lahf_lm
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm
constant_tsc pni monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr
lahf_lm

HTH







>
> My guess would rougly be arch/x86/kernel/processs.c
>
> 170         __monitor((void *)&current_thread_info()->flags, 0, 0);
>
> And perhaps this is a deference error, or it will be an even less
> obvious problem where the return from the nmi kgdb uses to sync the
> processors has created some kind of invalid context.  This may or may
> not be a direct problem with kgdb, but nothing in this area had really
> changed since the 2.6.26 kernel.
>
> Unfortunately I could not reproduce the problem.  If you consistently
> see this with each boot, but you do not see it on the 2.6.27 rc1 or
> 2.6.26 released kernel for instance, it is definitely worth bisecting,
> as the problem was caused elsewhere in the kernel.
>
>>  [<c02ad250>] ? kgdbts_break_test+0x0/0x30
>>  [<c02acdd1>] validate_simple_test+0x21/0xb0
>>  [<c02ad5a7>] run_simple_test+0x107/0x260
>>  [<c0153e00>] ? probe_kernel_read+0x20/0x40
>>  [<c02acec4>] kgdbts_put_char+0x14/0x20
>>  [<c014aa36>] put_packet+0x86/0xe0
>>  [<c014b650>] kgdb_handle_exception+0x2f0/0xd90
>>  [<c0114cc8>] kgdb_notify+0x58/0x180
>>  [<c013c33d>] notifier_call_chain+0x2d/0x60
>>  [<c013c38c>] __atomic_notifier_call_chain+0x1c/0x30
>>  [<c013c3ba>] atomic_notifier_call_chain+0x1a/0x20
>>  [<c013c44d>] notify_die+0x2d/0x30
>>  [<c01056ca>] die_nmi+0x3a/0x100
>>  [<c0112697>] nmi_watchdog_tick+0x187/0x190
>>  [<c0106067>] do_nmi+0x87/0x2a0
>>  [<c04d5a73>] nmi_stack_correct+0x26/0x2b
>>  [<c011007b>] ? msr_seek+0xb/0x80
>>  [<c0109c02>] ? mwait_idle+0x32/0x40
>>  [<c01026c5>] cpu_idle+0x55/0xf0
>>  [<c04ae02e>] rest_init+0x4e/0x60
>>  [<c069794f>] start_kernel+0x23f/0x2c0
>>  [<c0697270>] ? unknown_bootoption+0x0/0x210
>>  [<c0697077>] __init_begin+0x77/0xb0
>
>
> Jason.
>
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