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Thursday, 17 July 2014

Interpreting an ESX/ESXi host purple diagnostic screen (1004250)

Purpose

This article provides information to decode ESX/ESXi host purple screen errors.
An ESX/ESXi purple screen error appears similar to:
Note: This article uses the information in this purple screen as an example.

Resolution

What is the VMkernel?

The VMkernel is the operating system core of ESX/ESXi. The kernel handles resource scheduling and device IO. Device IO is handled by the VMware network and storage stacks, which serve as a layer between the virtual file system, network devices and the device drivers that control physical devices.

Interpreting the purple diagnostic screen

If the VMkernel experiences an error, the error displays in a purple diagnostic screen. The purple diagnostic screen looks similar to:
VMware ESX Server [Releasebuild-98103
PCPU 1 locked up. Failed to ack TLB invalidate.
frame=0x3a37d98 ip=0x625e94 cr2=0x0 cr3=0x40c66000 cr4=0x16c
es=0xffffffff ds=0xffffffff fs=0xffffffff gs=0xffffffff
eax=0xffffffff ebx=0xffffffff ecx=0xffffffff edx=0xffffffff
ebp=0x3a37ef4 esi=0xffffffff edi=0xffffffff err=-1 eflags=0xffffffff
*0:1037/helper1-4 1:1107/vmm0:Fagi 2:1121/vmware-vm 3:1122/mks:Franc
0x3a37ef4:[0x625e94]Panic+0x17 stack: 0x833ab4, 0x3a37f10, 0x3a37f48
0x3a37f04:[0x625e94]Panic+0x17 stack: 0x833ab4, 0x1, 0x14a03a0
0x3a37f48:[0x64bfa4]TLBDoInvalidate+0x38f stack: 0x3a37f54, 0x40, 0x2
0x3a37f70:[0x66da4d]XMapForceFlush+0x64 stack: 0x0, 0x4d3a, 0x0
0x3a37fac:[0x652b8b]helpFunc+0x2d2 stack: 0x1, 0x14a4580, 0x0
0x3a37ffc:[0x750902]CpuSched_StartWorld+0x109 stack: 0x0, 0x0, 0x0
0x3a38000:[0x0]blk_dev+0xfd76461f stack: 0x0, 0x0, 0x0 
VMK uptime: 7:05:43:45.014 TSC: 1751259712918392
Starting coredump to disk Starting coredump to disk Dumping using slot 1 of 1...using slot 1 of 1... log

Here is a breakdown of each section of the above purple diagnostic screen:
  • The Product and Build:

    VMware ESX Server [Releasebuild-98103]

    This section of the purple diagnostic screen identifies the product and build that has experienced the error. In this example, the product is VMware ESX Server build 98103.
  • The Error Message:

    PCPU 1 locked up. Failed to ack TLB invalidate
    This section of the purple diagnostic screen identifies the error message that has been reported. There are only a finite number of error messages that can be reported. These error messages are discussed later in this article.
  • The CPU Registers:

    frame=0x3a37d98 ip=0x625e94 cr2=0x0 cr3=0x40c66000 cr4=0x16c
    es=0xffffffff ds=0xffffffff fs=0xffffffff gs=0xffffffff
    eax=0xffffffff ebx=0xffffffff ecx=0xffffffff edx=0xffffffff
    ebp=0x3a37ef4 esi=0xffffffff edi=0xffffffff err=-1 eflags=0xffffffff
    These are the values that were in the physical CPU registers at the time of the error. The information in these registers may vary greatly between VMkernel errors. These registers can only be used internally when debugging a core dump of the VMkernel error. For more information about these registers, see http://www.intel.com/products/processor/manuals/ for Intel and http://support.amd.com/us/psearch/Pages/psearch.aspx for AMD. At the AMD site, search for the Architecture Programmer's manual for your specific processor type. 

    Note: The preceding links were correct as of March 28, 2013. If you find the links to be broken, provide feedback on the article and a VMware employee will update the article as necessary. 
  • The Physical CPU:

    *0:1037/helper1-4 1:1107/vmm0:Fagi 2:1121/vmware-vm 3:1122/mks:Franc

    This section of the purple diagnostic screen identifies the physical CPU that was running instructions during the VMkernel error. In the example, the * beside the 0 indicates that physical CPU 0 was running an operation at the time of the failure. In newer versions of ESX, instead of including an *, the preceding letters CPU are included. For example, if the same error as the above were to occur in newer versions of VMware ESX, the same line appears as: 

    CPU0:1037/helper1-4 cpu1:1107/vmm0:Fagi cpu2:1121/vmware-vm cpu3:1122/mks:Franc. 
    This section of the purple diagnostic screen also describes the world (process) that was running on the CPU at the time of the error. In the above example, the userworld running was helper1-4. 

    Note    : The name of the process may be truncated.
  • The Stack Trace:

    0x3a37ef4:[0x625e94]Panic+0x17 stack: 0x833ab4, 0x3a37f10, 0x3a37f48
    0x3a37f04:[0x625e94]Panic+0x17 stack: 0x833ab4, 0x1, 0x14a03a0
    0x3a37f48:[0x64bfa4]TLBDoInvalidate+0x38f stack: 0x3a37f54, 0x40, 0x2
    0x3a37f70:[0x66da4d]XMapForceFlush+0x64 stack: 0x0, 0x4d3a, 0x0
    0x3a37fac:[0x652b8b]helpFunc+0x2d2 stack: 0x1, 0x14a4580, 0x0
    0x3a37ffc:[0x750902]CpuSched_StartWorld+0x109 stack: 0x0, 0x0, 0x0
    0x3a38000:[0x0]blk_dev+0xfd76461f stack: 0x0, 0x0, 0x0

    The stack represents what the VMkernel was doing at the time of the error. In this example, it was trying to clear memory page tables (TLB). This information is a vital tool in the diagnosis of purple screen errors by evaluating the actions of the kernel at the time of the error.
  • The Uptime:

    VMK uptime: 7:05:43:45.014 TSC: 1751259712918392

    This section indicates how long a server had been running since the last boot. In this example, the ESX host was running for 7 days, 5 hours, 43 minutes and 45.014 seconds. The TSC value is the number of CPU clock cycles that have elapsed since the server was started.
  • The Core Dump:

    Starting coredump to disk Starting coredump to disk Dumping using slot 1 of 1...using slot 1 of 1... log
    This section of the purple diagnostic screen indicates that the contents of the VMkernel memory are being copied to the vmkcore partition. 

Using the error message of the purple diagnostic screen to troubleshoot a vmkernel error

The VMkernel error message generated by the purple screen can be used to identify the cause of the issue. The number of error messages that can be produced are finite. This is a list of known VMkernel error messages.
  • Type: Console Oops
    Example Error:COS Error: Oops
    Description: An ESX host can fail and cause a purple screen when there is a Service Console oops. Unlike most purple screen errors, it is not triggered by the VMkernel. Instead the error is triggered by the Service Console and occurs at the Linux level. These purple screen errors contain additional information from the Linux kernel. For more information about Console Oops, seeUnderstanding an "Oops" purple diagnostic screen (1006802). 
  • Type: Lost Heartbeat
    Example Error:Lost Heartbeat
    Description: The ESX VMkernel and the Service Console Linux kernel run at the same time on ESX. The Service Console Linux kernel runs a process called vmnixhbd, which heartbeats the VMkernel as long as it is able to allocate and free a page of memory. If no heartbeats are received before a timeout period of 30 minutes, the VMkernel triggers a COS Panic and a purple diagnostics screen that mentions a Lost Heartbeat. For more information on Lost Heatbeats, see Understanding a "Lost Heartbeat" purple diagnostic screen (1009525) .
  • Type: Assert
    Example Error:ASSERT bora/vmkernel/main/pframe_int.h:527 
    Description: Assert errors are software errors, because they are related to assumptions on which the program is based. This type of purple screen error is primarily caused by software issues. For more information on the assert error message, see Understanding ASSERT and NOT_IMPLEMENTED purple diagnostic screens (1019956). 
  • Type: Not Implemented
    Example Error: NOT_IMPLEMENTED /build/mts/release/bora-84374/bora/vmkernel/main/util.c:83
    Description: A not implemented error message occurs when the code encounters a situation that it was not designed to handle. For more information, see Understanding ASSERT and NOT_IMPLEMENTED purple diagnostic screens (1019956). 
  • Type: Spin count exceeded / Possible deadlock
    Example Error: Spin count exceeded (iplLock) - possible deadlock
    Description: A VMware ESX host may report a Spin count exceeded and possible deadlock in a purple diagnostic screen when a thread is attempting to execute in the critical section of code. Since it was trying to enter the critical section, the thread needed to poll a mutex for a lock prior to executing the code by conducting a spinlock operation. The thread continues to poll the mutex during the spinlock operation, but there is a certain limit of how many times it polls the mutex. For more information on Spin count exceeded errors, see Understanding a "Spin count exceeded" purple diagnostic screen (1020105). 
  • Type: Failed to ack TLB invalidate
    Example Error: PCPU 1 locked up. Failed to ack TLB invalidate.
    Description: Physical CPUs fail when trying to clear memory page tables. For more information, see Understanding a Failed to ack TLB invalidate purple diagnostic screen (1020214).
A purple diagnostic screen can also come in the form of an Exception. An Exception Handler is a computer hardware mechanism designed to handle some condition that changes the normal flow of execution (Division by Zero, Page Fault, etc). There is no trace from handlers, so you need logging to determine if handler faulted (or single step debugging). This is a list of common exceptions:
  • Type: Exception 13 (General Protection Fault)
    Example Error: #GP Exception(13) in world 4130:helper13-0 @ 0x41803399e303
    Description: A general protection fault (Exception 13) occurs under one of the following circumstances: the page being requested does not belong to the program requesting it (and not mapped in program memory), or the program does not have rights to perform a read or write operation on the page. For more information on Exception 13 or Page Fault, see Understanding Exception 13 and Exception 14 purple diagnostic screen events (1020181). 
  • Type: Exception 14 (Page Fault)
    Example Error: #PF Exception type 14 in world 136:helper0-0 @ 0x4a8e6e
    Description: A page fault (Exception 14) occurs when the page being requested has not been successfully loaded into memory. For more information on Exception 14 or Page Fault, see Understanding Exception 13 and Exception 14 purple diagnostic screen events (1020181). 
  • Type: Exception 18 (Machine Check Exception)
    Example Error: Machine Check Exception: Unable to continue
    Example Error: Hardware (Machine) Error
    Description: A Machine Check Exception (MCE) is generated by the hardware and reported by the host. Consult your hardware vendor in the event of an MCE. By evaluating the information presented, it is possible to identify the individual component reporting the error. For more information on MCE, see Decoding Machine Check Exception (MCE) output after a purple screen error (1005184).
If your VMware ESX or ESXi host experiences an error similar to one of these that does not point you to a general article, search for the error message and stack trace information within the Knowledge Base. If the error has not been documented within the Knowledge Base, collect the diagnostic information from the VMware ESX host and submit a support request. For more information, see Collecting diagnostic information for VMware products (1008524) and and How to Submit a Support Request.

Using the pattern analysis to troubleshoot multiple vmkernel errors on the same ESX host

In the event that you experience multiple purple diagnostic screens from the same VMware ESX host, you can use the sample of multiple purple diagnostic screens to determine the likeliness of an issue being related to hardware or software. This can be done by identifying patterns in these sections of the purple diagnostic screen:
  • The error message and the stack trace: 

    • If the error message and stack vary greatly between vmkernel errors, this indicates that software is not always hitting the same error. Although inconclusive, this may indicate a hardware issue.
    • If the error message and the stack are always identical between vmkernel errors, this indicates that software is always hitting the same error. Although inconclusive, this may indicate a software issue.
    • For more information about the error message you are experiencing, refer to the above section about the specific error message.
  • The physical CPU: 

  • The world: 

    • If the world value remains the same across multiple VMkernel errors, this indicates that the vmkernel is failing when receiving instructions from the same world. Although inconclusive, this may indicate a world is sending instructions that may be triggering the VMkernel error.

Additional Information

This is a complete list of exceptions:
  • Exception Type 1 #DB: Debug Exception
  • Exception Type 2 NMI: Non-Maskable Interrupt
  • Exception Type 3 #BP: Breakpoint Exception
  • Exception Type 4 #OF: Overflow (INTO instruction)
  • Exception Type 5 #BR: Bounds check (BOUND instruction)
  • Exception Type 6 #UD: Invalid Opcode
  • Exception Type 7 #NM: Coprocessor not available
  • Exception Type 8 #DF: Double Fault
  • Exception Type 10 #TS: Invalid TSS
  • Exception Type 11 #NP: Segment Not Present
  • Exception Type 12 #SS: Stack Segment Fault
  • Exception Type 13 #GP: General Protection Fault
  • Exception Type 14 #PF: Page Fault
  • Exception Type 16 #MF: Coprocessor error
  • Exception Type 17 #AC: Alignment Check
  • Exception Type 18 #MC: Machine Check Exception
  • Exception Type 19 #XF: SIMD Floating-Point Exception
  • Exception Type 20-31: Reserved
  • Exception Type 32-255: User-defined (clock scheduler)
For more information about these Exceptions, see the Call and Return Operation for Interrupt or Exception Handling Procedures section ofIntel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1: Basic Architecture and Chapter 6: Interrupts and Exception Handling of Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3A.
Note: The preceding links were correct as of June 20, 2012. If you find a link is broken, provide feedback and a VMware employee will update the link.
There is a known issue when upgrading to vCenter Server 5.0, with ESXi 4.0 Updated 2 hosts.  See ESXi 4.0 hosts may experience a purple screen after vCenter Server is upgraded to 5.0 (2007269) for more information.
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