9:16 a.m.
On Tue, Oct 17, 2006 at 03:37:16PM -0400, Dave Anderson wrote:
> Hi Dave
>
> The following patch adds support for DWARF CFI based stack unwinding
> for crash. Since this method uses the call frame instructions for
> unwinding, it generates better backtraces than the existing backtrace
> mechanism. So when we have the unwind info available, this new method
> will be called, else we fall back to the existing mechanism.
>
> ... <this section moved below>
>
> Please provide your suggestions and comments.
>
> Thanks
> Rachita
Hi Rachita,
I've only been able to test this on a live system that has __start_unwind
and __end_unwind symbols, so I don't know what a backtrace with an
in-kernel exception frame, or a backtrace with a transition to the x86_64
IRQ stack or x86_64 exception stacks, would look like. If you have
an example, I'd be interested in seeing how they get handled.
Hi Dave
I was trying to use LKDTM to create various scenarios for crash dump.
To start with is the case of panic() in an interrupt context. Here I
am inducing a panic in handle_IRQ_event(), where I am registering a
jprobe. jp_handle_irq_event() is the jprobe handler which in turn calls
lkdtm_handler(). Running crash on the dump gives the following:
crash> bt
PID: 3898 TASK: ffff81022e988e20 CPU: 0 COMMAND: "slapd"
#0 [ffffffff8064bcf8] crash_kexec at ffffffff80152211
#1 [ffffffff8064bd40] machine_kexec at ffffffff8011a739
#2 [ffffffff8064bd80] crash_kexec at ffffffff8015222d
#3 [ffffffff8064be08] crash_kexec at ffffffff80152211
#4 [ffffffff8064be30] bust_spinlocks at ffffffff8011fd6d
#5 [ffffffff8064be40] panic at ffffffff80131410
#6 [ffffffff8064beb0] cdrom_pc_intr at ffffffff802ebe68
#7 [ffffffff8064bef0] ide_intr at ffffffff802df26f
#8 [ffffffff8064bf30] lkdtm_handler at ffffffff8800230d
#9 [ffffffff8064bf40] jp_handle_irq_event at ffffffff880023e8
#10 [ffffffff8064bf50] __do_IRQ at ffffffff801544f4
#11 [ffffffff8064bf58] __do_softirq at ffffffff80136b8f
#12 [ffffffff8064bf90] do_IRQ at ffffffff8010bda1
--- <IRQ stack> ---
#13 [ffff810229fd5f80] ret_from_intr at ffffffff80109b95
[exception RIP: unknown or invalid address]
RIP: 0000000000000000 RSP: 0000000000000000 RFLAGS: 00000000
RAX: ffffffffffffffff RBX: 00002afe35608c98 RCX: 00002afe359f7be4
RDX: 0000000000000033 RSI: 0000000000000202 RDI: 00007fff754bfbe0
RBP: 000000000000000a R8: 000055555590bca0 R9: 0000000000000000
R10: 00002afe35608c98 R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: 00002afe3597b1e0 R15: 000055555590b760
ORIG_RAX: 000000000000002b CS: 0000 SS: 0000
bt: WARNING: possibly bogus exception frame
RIP: 00002afe359f7be4 RSP: 00007fff754bfbe0 RFLAGS: 00000202
RAX: 00002afe35608c98 RBX: 000055555590b760 RCX: 0000000000000001
RDX: 00002afe35608c98 RSI: 0000000000000000 RDI: 000055555590bca0
RBP: ffffffff80109c0b R8: 000000000000000a R9: 0000000000000000
R10: 0000000000000000 R11: 00002afe3597b1e0 R12: 000055555590b760
R13: 00007fff754bfd38 R14: 0000000000000001 R15: 000055555590b760
ORIG_RAX: ffffffffffffffff CS: 0033 SS: 002b
crash> set unwind on
unwind: on
crash> bt
PID: 3898 TASK: ffff81022e988e20 CPU: 0 COMMAND: "slapd"
#0 [ffffffff8064bd88] crash_kexec at ffffffff80152211
#1 [ffffffff8064be48] panic at ffffffff80131410
#2 [ffffffff8064bf38] lkdtm_handler at ffffffff8800230d
--- <IRQ stack> ---
#3 [ffff810229fd5f80] ret_from_intr at ffffffff80109b95
[exception RIP: unknown or invalid address]
RIP: 0000000000000000 RSP: 0000000000000000 RFLAGS: 00000000
RAX: ffffffffffffffff RBX: 00002afe35608c98 RCX: 00002afe359f7be4
RDX: 0000000000000033 RSI: 0000000000000202 RDI: 00007fff754bfbe0
RBP: 000000000000000a R8: 000055555590bca0 R9: 0000000000000000
R10: 00002afe35608c98 R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: 00002afe3597b1e0 R15: 000055555590b760
ORIG_RAX: 000000000000002b CS: 0000 SS: 0000
bt: WARNING: possibly bogus exception frame
#4 [ffff810229fd5f80] common_interrupt at ffffffff80109b95
RIP: 00002afe359f7be4 RSP: 00007fff754bfbe0 RFLAGS: 00000202
RAX: 00002afe35608c98 RBX: 000055555590b760 RCX: 0000000000000001
RDX: 00002afe35608c98 RSI: 0000000000000000 RDI: 000055555590bca0
RBP: ffffffff80109c0b R8: 000000000000000a R9: 0000000000000000
R10: 0000000000000000 R11: 00002afe3597b1e0 R12: 000055555590b760
R13: 00007fff754bfd38 R14: 0000000000000001 R15: 000055555590b760
ORIG_RAX: ffffffffffffffff CS: 0033 SS: 002b
crash>
Comments?
In the stacktrace with 'unwind on', I was expecting to see jp_handle_irq_event
appear too (as frame 3)..Could my using a module to register the probe be the
reason ?
Thanks
Rachita