Help with decoding a NMI Watchdog interrupt on an Octeon

DISCUSSION Jan Rovins 3 participants 7 messages Jun 17, 2010 – Jun 21, 2010 MIPS

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Jan Rovins

author

2010-06-17 21:02 UTC #0 lore raw

Hi, I need some tips on how to go about deciphering the following NMI dump.

This is from a 2.6.21.7 kernel that came with the Cavium Networks 1.8.1 toolchain.
Is there any way to get some kind of back trace from this, or just find out which function it was in?

I have been playing around with objdump -x vmlinux but I cant zero in on anything this way.

Thanks in advance,

Jan
*** NMI Watchdog interrupt on Core 0x6 ***

       $0      0x0000000000000000      at      0x000000001010cce0
       v0      0x000000000000003d      v1      0x000000000000024a
       a0      0xffffffff807d7b70      a1      0x0000000000000000
       a2      0x000000000000024a      a3      0x0000000000000000
       a4      0xffffffff807d7b60      a5      0x0000000000000080
       a6      0x0000000000000001      a7      0xa800000411c62578
       t0      0x0000000000000001      t1      0xa80000048ef3e880
       t2      0xffffffff82d40000      t3      0xa80000041f48c000
       s0      0xc0000000000d9640      s1      0xc000000000088028
       s2      0x0000000000000000      s3      0x0000000000000180
       s4      0x0000000000000000      s5      0x0000000000000000
       s6      0xb7a89c196f513832      s7      0x0000000000000000
       t8      0xffffffff807d0000      t9      0xffffffff807d0000
       k0      0x0000000000000000      k1      0x00000000104dbcbf
       gp      0xa80000041f48c000      sp      0xa80000041f48fcf0
       s8      0x0000000000000000      ra      0xc0000000023c5004
       epc     0xffffffff802b10b8
       status  0x000000001058cce4      cause   0x0000000040008c08
       sum0    0x0000002100000000      en0     0x0000009300008000
Code around epc
       0xffffffff802b10a8      000000002406ffff
       0xffffffff802b10ac      0000000064a5ffff
       0xffffffff802b10b0      0000000010a60005
       0xffffffff802b10b4      0000000000000000
       0xffffffff802b10b8      0000000080620000
       0xffffffff802b10bc      000000001440fffb
       0xffffffff802b10c0      0000000064630001
       0xffffffff802b10c4      000000006463ffff
       0xffffffff802b10c8      0000000003e00008

David Daney

2010-06-17 21:25 UTC #1 lore raw

Quoted 23 lines · Jan Rovins

Hi, I need some tips on how to go about deciphering the following NMI dump.
This is from a 2.6.21.7 kernel that came with the Cavium Networks 1.8.1 toolchain.
Is there any way to get some kind of back trace from this, or just find out which function it was in?
I have been playing around with objdump -x vmlinux but I cant zero in on anything this way.
Thanks in advance,
Jan
*** NMI Watchdog interrupt on Core 0x6 *** $0 0x0000000000000000 at 0x000000001010cce0 v0 0x000000000000003d v1 0x000000000000024a a0 0xffffffff807d7b70 a1 0x0000000000000000 a2 0x000000000000024a a3 0x0000000000000000 a4 0xffffffff807d7b60 a5 0x0000000000000080 a6 0x0000000000000001 a7 0xa800000411c62578 t0 0x0000000000000001 t1 0xa80000048ef3e880 t2 0xffffffff82d40000 t3 0xa80000041f48c000 s0 0xc0000000000d9640 s1 0xc000000000088028

Quoted 8 lines

s2 0x0000000000000000 s3 0x0000000000000180 s4 0x0000000000000000 s5 0x0000000000000000 s6 0xb7a89c196f513832 s7 0x0000000000000000 t8 0xffffffff807d0000 t9 0xffffffff807d0000 k0 0x0000000000000000 k1 0x00000000104dbcbf gp 0xa80000041f48c000 sp 0xa80000041f48fcf0 s8 0x0000000000000000 ra 0xc0000000023c5004 epc 0xffffffff802b10b8

You may want to verify that epc value is being loaded from C0_ErrorEPC rather than C0_EPC. SDK-1.8.1 gets this wrong.

Look in watchgog.c:octeon_watchdog_nmi_stage3.

Once you have it printing the ErrorEPC value, the trace actually tells you what was happening when the NMI fired.

objdump -d vmlinux will give you a disassembly of the kernel, and away you go.

David Daney

Quoted 15 lines

status 0x000000001058cce4 cause 0x0000000040008c08 sum0 0x0000002100000000 en0 0x0000009300008000 Code around epc
0xffffffff802b10a8 000000002406ffff 0xffffffff802b10ac 0000000064a5ffff 0xffffffff802b10b0 0000000010a60005 0xffffffff802b10b4 0000000000000000 0xffffffff802b10b8 0000000080620000 0xffffffff802b10bc 000000001440fffb 0xffffffff802b10c0 0000000064630001 0xffffffff802b10c4 000000006463ffff 0xffffffff802b10c8 0000000003e00008

Kevin D. Kissell

2010-06-17 21:27 UTC #2 lore raw

In reply to Jan Rovins

NMI is just an input pin, so you'd really need to know what it's connected to in the system you're working on. Typically, it's tied to some kind of memory bus time-out, but it could be other things. Depending on what it's hooked up to, knowing what code was executing when it came in may be completely useless. *If* it's hooked up to a bus time-out, *and* the instruction that caused the time-out was a load, *and* the time-out and NMI occurred *after* the processor got to the instruction that consumes the load value (pretty likely if the first two conditions are met), *then* looking at disassembled kernel code (mips-linux-objdump --disassemble vmlinux) at the ErrorEPC address, *not* the address in EPC, which will have latched the address of the last recoverable exception (which NMI is not, strictly speaking). That instruction should be the consumer of the bad load, so one of its input registers should be the target of that load. If it's a two-input instruction, e.g. add r1,r2,r3, then it could be either r2 or r3, and you have to work your way backwords up the code flow to find out where the r2 and r3 values came from, respectively. *Usually* it's possible to identify the load, thus the register used as a base address, and see that the base address register was trashed, at which point you can start forming hypotheses as to how that could have happened.

Of course, in the dump below, we don't see ErrorEPC. I've never been able to figure out why so many kernel register dumps skip that register, especially for NMI reporting. But unless you're able to reproduce this with a kernel that you build yourself, so that you can fix the instrumentation, it's going to be tough. So "Plan B" would be to make sure that any removable memory DIMMs have been properly seated, and double-check that the actual memory capacity corresponds to whatever boot parameters are being passed to the kernel. In otherwords, if you can't debug the kernel, pray that it's a hardware or operator error. ;o)

Regards,

Kevin K.

Quoted 42 lines · Jan Rovins

Hi, I need some tips on how to go about deciphering the following NMI dump.

This is from a 2.6.21.7 kernel that came with the Cavium Networks 1.8.1 toolchain.
Is there any way to get some kind of back trace from this, or just find out which function it was in?

I have been playing around with objdump -x vmlinux but I cant zero in on anything this way.

Thanks in advance,

Jan
*** NMI Watchdog interrupt on Core 0x6 ***

       $0      0x0000000000000000      at      0x000000001010cce0
       v0      0x000000000000003d      v1      0x000000000000024a
       a0      0xffffffff807d7b70      a1      0x0000000000000000
       a2      0x000000000000024a      a3      0x0000000000000000
       a4      0xffffffff807d7b60      a5      0x0000000000000080
       a6      0x0000000000000001      a7      0xa800000411c62578
       t0      0x0000000000000001      t1      0xa80000048ef3e880
       t2      0xffffffff82d40000      t3      0xa80000041f48c000
       s0      0xc0000000000d9640      s1      0xc000000000088028
       s2      0x0000000000000000      s3      0x0000000000000180
       s4      0x0000000000000000      s5      0x0000000000000000
       s6      0xb7a89c196f513832      s7      0x0000000000000000
       t8      0xffffffff807d0000      t9      0xffffffff807d0000
       k0      0x0000000000000000      k1      0x00000000104dbcbf
       gp      0xa80000041f48c000      sp      0xa80000041f48fcf0
       s8      0x0000000000000000      ra      0xc0000000023c5004
       epc     0xffffffff802b10b8
       status  0x000000001058cce4      cause   0x0000000040008c08
       sum0    0x0000002100000000      en0     0x0000009300008000
Code around epc
       0xffffffff802b10a8      000000002406ffff
       0xffffffff802b10ac      0000000064a5ffff
       0xffffffff802b10b0      0000000010a60005
       0xffffffff802b10b4      0000000000000000
       0xffffffff802b10b8      0000000080620000
       0xffffffff802b10bc      000000001440fffb
       0xffffffff802b10c0      0000000064630001
       0xffffffff802b10c4      000000006463ffff
       0xffffffff802b10c8      0000000003e00008

David Daney

2010-06-17 21:51 UTC #3 lore raw

Quoted 2 lines · Kevin D. Kissell

NMI is just an input pin, so you'd really need to know what it's connected to in the system you're working on.

In this case, the NMI is likely being asserted by the watchdog. So if you are stuck in a loop with interrupts disabled, the register dump might help you figure out where things are stuck. But as you say below, knowing the value of the ErrorEPC register is critical.

David Daney

Quoted 84 lines

Typically, it's tied to
some kind of memory bus time-out, but it could be other things. Depending on what it's hooked up to, knowing what code was executing when it came in may be completely useless. *If* it's hooked up to a bus time-out, *and* the instruction that caused the time-out was a load, *and* the time-out and NMI occurred *after* the processor got to the instruction that consumes the load value (pretty likely if the first two conditions are met), *then* looking at disassembled kernel code (mips-linux-objdump --disassemble vmlinux) at the ErrorEPC address, *not* the address in EPC, which will have latched the address of the last recoverable exception (which NMI is not, strictly speaking). That instruction should be the consumer of the bad load, so one of its input registers should be the target of that load. If it's a two-input instruction, e.g. add r1,r2,r3, then it could be either r2 or r3, and you have to work your way backwords up the code flow to find out where the r2 and r3 values came from, respectively. *Usually* it's possible to identify the load, thus the register used as a base address, and see that the base address register was trashed, at which point you can start forming hypotheses as to how that could have happened.
Of course, in the dump below, we don't see ErrorEPC. I've never been able to figure out why so many kernel register dumps skip that register, especially for NMI reporting. But unless you're able to reproduce this with a kernel that you build yourself, so that you can fix the instrumentation, it's going to be tough. So "Plan B" would be to make sure that any removable memory DIMMs have been properly seated, and double-check that the actual memory capacity corresponds to whatever boot parameters are being passed to the kernel. In otherwords, if you can't debug the kernel, pray that it's a hardware or operator error. ;o)
Regards,
Kevin K.
Quoted 46 lines · Jan Rovins
Hi, I need some tips on how to go about deciphering the following NMI dump.
This is from a 2.6.21.7 kernel that came with the Cavium Networks 1.8.1 toolchain.
Is there any way to get some kind of back trace from this, or just find out which function it was in?
I have been playing around with objdump -x vmlinux but I cant zero in on anything this way.
Thanks in advance,
Jan
*** NMI Watchdog interrupt on Core 0x6 *** $0 0x0000000000000000 at 0x000000001010cce0 v0 0x000000000000003d v1 0x000000000000024a a0 0xffffffff807d7b70 a1 0x0000000000000000 a2 0x000000000000024a a3 0x0000000000000000 a4 0xffffffff807d7b60 a5 0x0000000000000080 a6 0x0000000000000001 a7 0xa800000411c62578 t0 0x0000000000000001 t1 0xa80000048ef3e880 t2 0xffffffff82d40000 t3 0xa80000041f48c000 s0 0xc0000000000d9640 s1 0xc000000000088028 s2 0x0000000000000000 s3 0x0000000000000180 s4 0x0000000000000000 s5 0x0000000000000000 s6 0xb7a89c196f513832 s7 0x0000000000000000 t8 0xffffffff807d0000 t9 0xffffffff807d0000 k0 0x0000000000000000 k1 0x00000000104dbcbf gp 0xa80000041f48c000 sp 0xa80000041f48fcf0 s8 0x0000000000000000 ra 0xc0000000023c5004 epc 0xffffffff802b10b8
status 0x000000001058cce4 cause 0x0000000040008c08 sum0 0x0000002100000000 en0 0x0000009300008000 Code around epc
0xffffffff802b10a8 000000002406ffff 0xffffffff802b10ac 0000000064a5ffff 0xffffffff802b10b0 0000000010a60005 0xffffffff802b10b4 0000000000000000 0xffffffff802b10b8 0000000080620000 0xffffffff802b10bc 000000001440fffb 0xffffffff802b10c0 0000000064630001 0xffffffff802b10c4 000000006463ffff 0xffffffff802b10c8 0000000003e00008

Jan Rovins

author

2010-06-19 19:13 UTC #4 lore raw

Quoted 5 lines · David Daney

Quoted 2 lines · Kevin D. Kissell
NMI is just an input pin, so you'd really need to know what it's connected to in the system you're working on.
In this case, the NMI is likely being asserted by the watchdog. So if you are stuck in a loop with interrupts disabled, the register dump might help you figure out where things are stuck. But as you say below, knowing the value of the ErrorEPC register is critical.

Thank you David & Kevin for the detailed information.

Yes, in my case it's the watchdog, when I turn the watchdog off, the machine just hangs, with no NMI dump.

Ok, I added the code to Print out the ErrorEPC, and got:
ErrorEpc 0xc0000000023c5004
This address is not in vmlinux, but is the address of a loaded module.

So, I poked around in /sys/module/ until I found one that had that address range:
cat /sys/module/linux_bcm_core/sections/.text :0xc000000001c4e000

And then did an objdump on this module. Since the module dump did not contain the actual addresses that it was running from, I doctored up the offsets by using the .text address from /sys/module/ of where the module actually loaded. objdump.cavium -d --adjust-vma 0xc000000001c4e000 linux-bcm-core.ko

Just want to check if all this sounds correct so far? is my objdump valid with the .text offset?

I got a hit on the ErrorEPC value in my dump:
c0000000023c5004: 08000000 j c000000000000000 <sal_dma_alloc-0x1c4e000>
Does this mean that the lockup happened at the jump, or after the jump?
I am also a little confused about the jump location, I am used to seeing <symbol+offset> but this has <symbol-offset>. is that valid?

I have a feeling that is referring to a symbol in a different module, since sal_dma_alloc is the first symbol of the module that I am looking at. and that module is tightly coupled to 2 other modules.

Is the c000000000000000 the actual address of the jump? can I then just look it up the same way that I found the ErrorEPC address in a module, or do I have to work backwards from <sal_dma_alloc-0x1c4e000> to find the offset into the previous module that it is referring to?

Jan

Quoted 87 lines

David Daney
Quoted 84 lines
Typically, it's tied to
some kind of memory bus time-out, but it could be other things. Depending on what it's hooked up to, knowing what code was executing when it came in may be completely useless. *If* it's hooked up to a bus time-out, *and* the instruction that caused the time-out was a load, *and* the time-out and NMI occurred *after* the processor got to the instruction that consumes the load value (pretty likely if the first two conditions are met), *then* looking at disassembled kernel code (mips-linux-objdump --disassemble vmlinux) at the ErrorEPC address, *not* the address in EPC, which will have latched the address of the last recoverable exception (which NMI is not, strictly speaking). That instruction should be the consumer of the bad load, so one of its input registers should be the target of that load. If it's a two-input instruction, e.g. add r1,r2,r3, then it could be either r2 or r3, and you have to work your way backwords up the code flow to find out where the r2 and r3 values came from, respectively. *Usually* it's possible to identify the load, thus the register used as a base address, and see that the base address register was trashed, at which point you can start forming hypotheses as to how that could have happened.
Of course, in the dump below, we don't see ErrorEPC. I've never been able to figure out why so many kernel register dumps skip that register, especially for NMI reporting. But unless you're able to reproduce this with a kernel that you build yourself, so that you can fix the instrumentation, it's going to be tough. So "Plan B" would be to make sure that any removable memory DIMMs have been properly seated, and double-check that the actual memory capacity corresponds to whatever boot parameters are being passed to the kernel. In otherwords, if you can't debug the kernel, pray that it's a hardware or operator error. ;o)
Regards,
Kevin K.
Quoted 46 lines · Jan Rovins
Hi, I need some tips on how to go about deciphering the following NMI dump.
This is from a 2.6.21.7 kernel that came with the Cavium Networks 1.8.1 toolchain.
Is there any way to get some kind of back trace from this, or just find out which function it was in?
I have been playing around with objdump -x vmlinux but I cant zero in on anything this way.
Thanks in advance,
Jan
*** NMI Watchdog interrupt on Core 0x6 *** $0 0x0000000000000000 at 0x000000001010cce0 v0 0x000000000000003d v1 0x000000000000024a a0 0xffffffff807d7b70 a1 0x0000000000000000 a2 0x000000000000024a a3 0x0000000000000000 a4 0xffffffff807d7b60 a5 0x0000000000000080 a6 0x0000000000000001 a7 0xa800000411c62578 t0 0x0000000000000001 t1 0xa80000048ef3e880 t2 0xffffffff82d40000 t3 0xa80000041f48c000 s0 0xc0000000000d9640 s1 0xc000000000088028 s2 0x0000000000000000 s3 0x0000000000000180 s4 0x0000000000000000 s5 0x0000000000000000 s6 0xb7a89c196f513832 s7 0x0000000000000000 t8 0xffffffff807d0000 t9 0xffffffff807d0000 k0 0x0000000000000000 k1 0x00000000104dbcbf gp 0xa80000041f48c000 sp 0xa80000041f48fcf0 s8 0x0000000000000000 ra 0xc0000000023c5004 epc 0xffffffff802b10b8
status 0x000000001058cce4 cause 0x0000000040008c08 sum0 0x0000002100000000 en0 0x0000009300008000 Code around epc
0xffffffff802b10a8 000000002406ffff 0xffffffff802b10ac 0000000064a5ffff 0xffffffff802b10b0 0000000010a60005 0xffffffff802b10b4 0000000000000000 0xffffffff802b10b8 0000000080620000 0xffffffff802b10bc 000000001440fffb 0xffffffff802b10c0 0000000064630001 0xffffffff802b10c4 000000006463ffff 0xffffffff802b10c8 0000000003e00008

Jan Rovins

author

2010-06-21 05:55 UTC #5 lore raw

Some additions & corrections to the previous:

Quoted 36 lines

-----Original Message-----
From: [email protected] [mailto:linux-mips-bounce@linux- mips.org] On Behalf Of Jan Rovins
Sent: Saturday, June 19, 2010 3:14 PM
To: David Daney
Cc: Kevin D. Kissell; [email protected]
Subject: Re: Help with decoding a NMI Watchdog interrupt on an Octeon
Quoted 8 lines · David Daney
Quoted 2 lines · Kevin D. Kissell
NMI is just an input pin, so you'd really need to know what it's connected to in the system you're working on.
In this case, the NMI is likely being asserted by the watchdog. So if you are stuck in a loop with interrupts disabled, the register dump might help you figure out where things are stuck. But as you say below, knowing the value of the ErrorEPC register is critical.
Thank you David & Kevin for the detailed information.
Yes, in my case it's the watchdog, when I turn the watchdog off, the machine just hangs, with no NMI dump.
Ok, I added the code to Print out the ErrorEPC, and got:
ErrorEpc 0xc0000000023c5004
This address is not in vmlinux, but is the address of a loaded module.
So, I poked around in /sys/module/ until I found one that had that address range:
cat /sys/module/linux_bcm_core/sections/.text :0xc000000001c4e000
And then did an objdump on this module. Since the module dump did not contain the actual addresses that it was running from, I doctored up the offsets by using the .text address from /sys/module/ of where the module actually loaded.
objdump.cavium -d --adjust-vma 0xc000000001c4e000 linux-bcm-core.ko

Quoted 6 lines

Just want to check if all this sounds correct so far? is my objdump valid with the .text offset?
I got a hit on the ErrorEPC value in my dump:
c0000000023c5004: 08000000 j c000000000000000
<sal_dma_alloc-0x1c4e000>

This line of code was inside a function called _default_assert, which on assertion failure, did a printk() and went into an intentional infinite loop, which explains the NMI dump. The only thing that puzzles me now, is that the assert failure printk rarely displayed. Could that be because it was called while interrupts were turned off? I suppose that would stop it from showing up in /var/log/messages.

The assembly still does not make sense to me (first time with MIPS assembly) but on examining the C code I think I understand what's going on here.

Quoted 107 lines

Does this mean that the lockup happened at the jump, or after the jump? I am also a little confused about the jump location, I am used to seeing <symbol+offset> but this has <symbol-offset>. is that valid?
I have a feeling that is referring to a symbol in a different module, since sal_dma_alloc is the first symbol of the module that I am looking at. and that module is tightly coupled to 2 other modules.
Is the c000000000000000 the actual address of the jump? can I then just look it up the same way that I found the ErrorEPC address in a module, or do I have to work backwards from <sal_dma_alloc-0x1c4e000> to find the offset into the previous module that it is referring to?
Jan
Quoted 9 lines
David Daney
Quoted 7 lines
Typically, it's tied to
some kind of memory bus time-out, but it could be other things. Depending on what it's hooked up to, knowing what code was executing when it came in may be completely useless. *If* it's hooked up to a bus time-out, *and* the instruction that caused the time-out was a load, *and* the time-out and NMI occurred *after* the processor got to the instruction that consumes the load value (pretty likely if the first
two
Quoted 9 lines
Quoted 9 lines
conditions are met), *then* looking at disassembled kernel code (mips-linux-objdump --disassemble vmlinux) at the ErrorEPC address, *not* the address in EPC, which will have latched the address of the last recoverable exception (which NMI is not, strictly speaking). That instruction should be the consumer of the bad load, so one of its input registers should be the target of that load. If it's a two-input instruction, e.g. add r1,r2,r3, then it could be either r2 or r3, and you have to work your way backwords up the code flow to find out where the r2 and r3 values came from, respectively. *Usually* it's possible
to
Quoted 2 lines
Quoted 2 lines
identify the load, thus the register used as a base address, and see that the base address register was trashed, at which point you can
start
Quoted 4 lines
Quoted 4 lines
forming hypotheses as to how that could have happened.
Of course, in the dump below, we don't see ErrorEPC. I've never been able to figure out why so many kernel register dumps skip that
register,
Quoted 7 lines
Quoted 7 lines
especially for NMI reporting. But unless you're able to reproduce this with a kernel that you build yourself, so that you can fix the instrumentation, it's going to be tough. So "Plan B" would be to make sure that any removable memory DIMMs have been properly seated, and double-check that the actual memory capacity corresponds to whatever boot parameters are being passed to the kernel. In otherwords, if you can't debug the kernel, pray that it's a hardware or operator error.
;o)
Quoted 56 lines
Quoted 55 lines
Regards,
Kevin K.
Quoted 46 lines · Jan Rovins
Hi, I need some tips on how to go about deciphering the following NMI dump.
This is from a 2.6.21.7 kernel that came with the Cavium Networks 1.8.1 toolchain.
Is there any way to get some kind of back trace from this, or just find out which function it was in?
I have been playing around with objdump -x vmlinux but I cant zero in on anything this way.
Thanks in advance,
Jan
*** NMI Watchdog interrupt on Core 0x6 *** $0 0x0000000000000000 at 0x000000001010cce0 v0 0x000000000000003d v1 0x000000000000024a a0 0xffffffff807d7b70 a1 0x0000000000000000 a2 0x000000000000024a a3 0x0000000000000000 a4 0xffffffff807d7b60 a5 0x0000000000000080 a6 0x0000000000000001 a7 0xa800000411c62578 t0 0x0000000000000001 t1 0xa80000048ef3e880 t2 0xffffffff82d40000 t3 0xa80000041f48c000 s0 0xc0000000000d9640 s1 0xc000000000088028 s2 0x0000000000000000 s3 0x0000000000000180 s4 0x0000000000000000 s5 0x0000000000000000 s6 0xb7a89c196f513832 s7 0x0000000000000000 t8 0xffffffff807d0000 t9 0xffffffff807d0000 k0 0x0000000000000000 k1 0x00000000104dbcbf gp 0xa80000041f48c000 sp 0xa80000041f48fcf0 s8 0x0000000000000000 ra 0xc0000000023c5004 epc 0xffffffff802b10b8
status 0x000000001058cce4 cause 0x0000000040008c08 sum0 0x0000002100000000 en0 0x0000009300008000 Code around epc
0xffffffff802b10a8 000000002406ffff 0xffffffff802b10ac 0000000064a5ffff 0xffffffff802b10b0 0000000010a60005 0xffffffff802b10b4 0000000000000000 0xffffffff802b10b8 0000000080620000 0xffffffff802b10bc 000000001440fffb 0xffffffff802b10c0 0000000064630001 0xffffffff802b10c4 000000006463ffff 0xffffffff802b10c8 0000000003e00008

David Daney

2010-06-21 16:22 UTC #6 lore raw

Quoted 38 lines · Jan Rovins

Some additions& corrections to the previous:
Quoted 36 lines
-----Original Message-----
From: [email protected] [mailto:linux-mips-bounce@linux- mips.org] On Behalf Of Jan Rovins
Sent: Saturday, June 19, 2010 3:14 PM
To: David Daney
Cc: Kevin D. Kissell; [email protected]
Subject: Re: Help with decoding a NMI Watchdog interrupt on an Octeon
Quoted 8 lines · David Daney
Quoted 2 lines · Kevin D. Kissell
NMI is just an input pin, so you'd really need to know what it's connected to in the system you're working on.
In this case, the NMI is likely being asserted by the watchdog. So if you are stuck in a loop with interrupts disabled, the register dump might help you figure out where things are stuck. But as you say below, knowing the value of the ErrorEPC register is critical.
Thank you David& Kevin for the detailed information.
Yes, in my case it's the watchdog, when I turn the watchdog off, the machine just hangs, with no NMI dump.
Ok, I added the code to Print out the ErrorEPC, and got:
ErrorEpc 0xc0000000023c5004
This address is not in vmlinux, but is the address of a loaded module.
So, I poked around in /sys/module/ until I found one that had that address range:
cat /sys/module/linux_bcm_core/sections/.text :0xc000000001c4e000
And then did an objdump on this module. Since the module dump did not contain the actual addresses that it was running from, I doctored up the offsets by using the .text address from /sys/module/ of where the module actually loaded.
objdump.cavium -d --adjust-vma 0xc000000001c4e000 linux-bcm-core.ko

When looking at kernel modules, it can be helpful to show the relocations as well, so add '-r' to your objdump command line...

Quoted 7 lines

Quoted 6 lines
Just want to check if all this sounds correct so far? is my objdump valid with the .text offset?
I got a hit on the ErrorEPC value in my dump:
c0000000023c5004: 08000000 j c000000000000000
<sal_dma_alloc-0x1c4e000>

... Once you turn on display or relocations, you can see where the jump is really going. The relocations are applied by the kernel when loading the module.

Quoted 11 lines

This line of code was inside a function called _default_assert, which on assertion failure, did a printk() and went into an intentional infinite loop, which explains the NMI dump. The only thing that puzzles me now, is that the assert failure printk rarely displayed. Could that be because it was called while interrupts were turned off? I suppose that would stop it from showing up in /var/log/messages.
The assembly still does not make sense to me (first time with MIPS assembly) but on examining the C code I think I understand what's going on here.

It seems like you may be onto the cause of the watchdog expiring, all that's left is to figure out how you get into this spot in the first place.

David Daney