记一次 .NET 某企业OA后端服务卡死分析-51CTO.COM

一、背景

1.讲故事

前段时间有位朋友微信找到我，说他生产机器上的 Console 服务看起来像是卡死了，也不生成日志，对方也收不到我的httpclient请求，不知道程序出现什么情况了，特来寻求帮助。

哈哈，一般来说卡死的情况在窗体程序（WinForm，WPF）上特别多，在 Console，WebApi 中相对较少，既然找到我，那就上 WinDbg 分析吧。

二、WinDbg 分析

1. 程序真的卡死了吗

程序之所以能跑的梭梭响，全靠线程帮忙，如果玩不转可能就是线程上出了点什么问题，接下来使用 !t 展示下线程列表。


0:000> !t
ThreadCount:      124
UnstartedThread:  0
BackgroundThread: 105
PendingThread:    0
DeadThread:       18
Hosted Runtime:   no
                                                                                                            Lock  
 DBG   ID     OSID ThreadOBJ           State GC Mode     GC Alloc Context                  Domain           Count Apt Exception
   0    1     65ec 000002097A4BF390    2a020 Preemptive  0000000000000000:0000000000000000 000002097a4bea20 -00001 MTA 
   3    2    15afc 000002097A50BA10    2b220 Preemptive  00000209060BE8F8:00000209060BEBE8 000002097a4bea20 -00001 MTA (Finalizer) 
   4    3    11d20 000002097A524EC0  102a220 Preemptive  0000000000000000:0000000000000000 000002097a4bea20 -00001 MTA (Threadpool Worker) 
   5    9     b8a4 000002097DE10290  3029220 Preemptive  0000000000000000:0000000000000000 000002097a4bea20 -00001 MTA (Threadpool Worker) 
   6   13    1b22c 000002097DE0ADB0  1029220 Preemptive  0000000000000000:0000000000000000 000002097a4bea20 -00001 MTA (Threadpool Worker) 
   7   16    1b0e8 000002097DE1A030  202b220 Preemptive  00000209063CB630:00000209063CC1F8 000002097a4bea20 -00001 MTA 
   8   17    138c8 000002097DE175C0  202b220 Preemptive  00000209063F71C0:00000209063F7BC8 000002097a4bea20 -00001 MTA 
   9   18    1afd0 000002097DE181E0  202b220 Preemptive  00000209064627E0:0000020906463598 000002097a4bea20 -00001 MTA 
  10   19    1ac48 000002097DE13310  202b220 Preemptive  000002090632D6C8:000002090632E0D8 000002097a4bea20 -00001 MTA 
  11   20    18704 000002097DE16390  202b220 Preemptive  00000209063FB5A8:00000209063FBBC8 000002097a4bea20 -00001 MTA 
  12   21    1ade4 000002097DE187F0  202b220 Preemptive  00000209062EA138:00000209062EA708 000002097a4bea20 -00001 MTA 
  13   22    13164 000002097DE13920  202b220 Preemptive  0000020906392108:0000020906392A38 000002097a4bea20 -00001 MTA 
  14   23    1b334 000002097DE169A0  202b220 Preemptive  00000209063CD9E8:00000209063CE1F8 000002097a4bea20 -00001 MTA 
  ...
 106  168    19e18 0000020927066770  a029220 Preemptive  0000000000000000:0000000000000000 000002097a4bea20 -00001 MTA (Threadpool Completion Port) 
 108  136     af74 0000020928590290  8029220 Preemptive  00000209063B60E0:00000209063B6408 000002097a4bea20 -00001 MTA (Threadpool Completion Port) 
 107   84     e7f0 000002097AD6B600  8029220 Preemptive  00000209063E3300:00000209063E3DD8 000002097a4bea20 -00001 MTA (Threadpool Completion Port)

一般来说卦中的 Lock Count 列表示当前线程所持有的托管锁个数，现在显示的 -00001 应该是命令不起效果了。。。不过没关系，我们还可以通过 !syncblk 来看下 lock 的情况，毕竟 95% 的锁场景都会用到它。


0:000> !syncblk
Index         SyncBlock MonitorHeld Recursion Owning Thread Info          SyncBlock Owner
  176 000002097E0DA1D8           17         1 00000209216A3500 132c8  71   00000209002c6a68 System.Object
  191 000002097E0DAC88           27         1 000002097ADC54F0 1ae90  53   00000209000185e8 System.IO.TextWriter+SyncTextWriter
-----------------------------
Total           270
CCW             0
RCW             0
ComClassFactory 0
Free            32

从卦中的 MonitorHeld=27 来看，表示这个 SyncTextWriter 对象当前有 13 个线程在等待，有 1 个线程在持有，那这个线程为什么没有退出呢？接下来可以切到 53 号线程上，查看下它的线程栈。


0:053> ~~[1ae90]s
ntdll!NtWriteFile+0x14:
00007ffd`a70df774 c3              ret
0:053> !clrstack 
OS Thread Id: 0x1ae90 (53)
        Child SP               IP Call Site
00000070505BDE88 00007ffda70df774 [InlinedCallFrame: 00000070505bde88] Interop+Kernel32.WriteFile(IntPtr, Byte*, Int32, Int32 ByRef, IntPtr)
00000070505BDE88 00007ffd32a7cbe2 [InlinedCallFrame: 00000070505bde88] Interop+Kernel32.WriteFile(IntPtr, Byte*, Int32, Int32 ByRef, IntPtr)
00000070505BDE50 00007ffd32a7cbe2 ILStubClass.IL_STUB_PInvoke(IntPtr, Byte*, Int32, Int32 ByRef, IntPtr)
00000070505BDF20 00007ffd3a2d6971 System.ConsolePal+WindowsConsoleStream.WriteFileNative(IntPtr, Byte[], Int32, Int32, Boolean)
00000070505BDF80 00007ffd3a2d672f System.ConsolePal+WindowsConsoleStream.Write(Byte[], Int32, Int32) [/_/src/libraries/System.Console/src/System/ConsolePal.Windows.cs @ 1131]
00000070505BDFD0 00007ffd377c05d9 System.IO.StreamWriter.Flush(Boolean, Boolean) [/_/src/libraries/System.Private.CoreLib/src/System/IO/StreamWriter.cs @ 260]
00000070505BE050 00007ffd3a2d6687 System.IO.StreamWriter.WriteLine(System.String)
00000070505BE0D0 00007ffd3a2d6472 System.IO.TextWriter+SyncTextWriter.WriteLine(System.String) [/_/src/libraries/System.Private.CoreLib/src/System/IO/TextWriter.cs @ 880]
00000070505BE130 00007ffd3a2d640d System.Console.WriteLine(System.String) [/_/src/libraries/System.Console/src/System/Console.cs @ 716]
00000070505BE160 00007ffd3a2375ab HCloud.xxx+d__2.MoveNext()
00000070505BEAE0 00007ffd37e19365 System.Runtime.CompilerServices.AsyncMethodBuilderCore.Start[[System.__Canon, System.Private.CoreLib]](System.__Canon ByRef) [/_/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncMethodBuilderCore.cs @ 63]
00000070505BEB40 00007ffd3a235cc3 HCloud.xxxx.Execute(Quartz.IJobExecutionContext)
00000070505BEBB0 00007ffd3a231264 Quartz.xxx+d__9.MoveNext()
00000070505BEE90 00007ffd3a230183 System.Runtime.CompilerServices.AsyncMethodBuilderCore.Start[[Quartz.Core.JobRunShell+d__9, Quartz]](d__9 ByRef) [/_/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncMethodBuilderCore.cs @ 63]
00000070505BEF10 00007ffd3a2300db System.Runtime.CompilerServices.AsyncTaskMethodBuilder.Start[[Quartz.Core.JobRunShell+d__9, Quartz]](d__9 ByRef) [/_/src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncTaskMethodBuilder.cs @ 33]
00000070505BEF40 00007ffd3a230082 Quartz.xxxxl.Run(System.Threading.CancellationToken)
00000070505BF020 00007ffd3a22ffc3 Quartz.Core.QuartzSchedulerThread+c__DisplayClass28_0.b__0()
00000070505BF060 00007ffd3939b71a System.Threading.Tasks.Task`1[[System.__Canon, System.Private.CoreLib]].InnerInvoke() [/_/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Future.cs @ 507]
00000070505BF0C0 00007ffd37d54431 System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(System.Threading.Thread, System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object) [/_/src/libraries/System.Private.CoreLib/src/System/Threading/ExecutionContext.cs @ 300]
00000070505BF110 00007ffd37d53657 System.Threading.Tasks.Task.ExecuteWithThreadLocal(System.Threading.Tasks.Task ByRef, System.Threading.Thread) [/_/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs @ 2352]
00000070505BF1C0 00007ffd37d50e04 System.Threading.ThreadPoolWorkQueue.Dispatch() [/_/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPool.cs @ 677]
00000070505BF690 00007ffd925ea7a3 [DebuggerU2MCatchHandlerFrame: 00000070505bf690]

仔细观察线程栈会很惊讶的发现，居然还能卡在 System.Console.WriteLine 方法上，挺奇怪的，为了探究原因，我们使用 k 命令看下非托管栈。


0:053> k 5
 # Child-SP          RetAddr               Call Site
00 00000070`505bddd8 00007ffd`a32febda     ntdll!NtWriteFile+0x14
01 00000070`505bdde0 00007ffd`32a7cbe2     KERNELBASE!WriteFile+0x7a
02 00000070`505bde50 00007ffd`3a2d6971     0x00007ffd`32a7cbe2
03 00000070`505bdf20 00007ffd`3a2d672f     System_Console!System.ConsolePal.WindowsConsoleStream.WriteFileNative+0x61
04 00000070`505bdf80 00007ffd`377c05d9     System_Console!System.ConsolePal.WindowsConsoleStream.Write+0x3f

0:053> ub ntdll!NtWriteFile+0x14
ntdll!NtDeviceIoControlFile+0x15:
00007ffd`a70df755 cd2e            int     2Eh
00007ffd`a70df757 c3              ret
00007ffd`a70df758 0f1f840000000000 nop     dword ptr [rax+rax]
ntdll!NtWriteFile:
00007ffd`a70df760 4c8bd1          mov     r10,rcx
00007ffd`a70df763 b808000000      mov     eax,8
00007ffd`a70df768 f604250803fe7f01 test    byte ptr [SharedUserData+0x308 (00000000`7ffe0308)],1
00007ffd`a70df770 7503            jne     ntdll!NtWriteFile+0x15 (00007ffd`a70df775)
00007ffd`a70df772 0f05            syscall

从上面的 syscall 系统调用关键词看，代码是将用户态的 ntdll!NtWriteFile 切到入了内核态的 nt!NtWriteFile 方法，那进入了内核态为什么没有返回呢？这又是一个值得思索的问题。

2. 为什么进入了内核态无返回

其实 ntdll!NtWriteFile 这个 win32 api 方法的第一个参数是一个 handle 的文件句柄，签名如下。


__kernel_entry NTSYSCALLAPI NTSTATUS NtWriteFile(
  [in]           HANDLE           FileHandle,
  [in, optional] HANDLE           Event,
  [in, optional] PIO_APC_ROUTINE  ApcRoutine,
  [in, optional] PVOID            ApcContext,
  [out]          PIO_STATUS_BLOCK IoStatusBlock,
  [in]           PVOID            Buffer,
  [in]           ULONG            Length,
  [in, optional] PLARGE_INTEGER   ByteOffset,
  [in, optional] PULONG           Key
);

可能 handle 在内核中被别人占用了，可以用 !handle 查看下 rcx 寄存器。


0:053> r
rax=0000000000000008 rbx=00000070505bdf50 rcx=0000000000000418
rdx=0000000000000000 rsi=0000000000000000 rdi=0000000000000418
rip=00007ffda70df774 rsp=00000070505bddd8 rbp=00000070505bdf10
 r8=0000000002000805  r9=0000000000000000 r10=0000020906191620
r11=00000070505bc8f8 r12=0000000000000100 r13=0000000000000053
r14=0000000000000077 r15=000002097adc54f0
iopl=0         nv up ei pl zr na po nc
cs=0033  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00000246
ntdll!NtWriteFile+0x14:
00007ffd`a70df774 c3              ret
0:053> !handle 0000000000000418 f
Handle 0000000000000418
  Type          File
  Attributes    0
  GrantedAccess 0x120196:
         ReadControl,Synch
         Write/Add,Append/SubDir/CreatePipe,WriteEA,ReadAttr,WriteAttr
  HandleCount   3
  PointerCount  65483
  No object specific information available

哈哈，其实也看不出什么，也没法进入内核态，所以下一步只能到网上搜搜看，其实有经验的朋友肯定猜出来了，应该是控制台启用了快捷编辑窗口，截图如下：

快捷编辑窗口简而言之就是用户可以在控制台上独占这个窗口，编辑一些内容，可一旦被用户独占，那程序侧就没法输出内容到控制台窗口上了，只能在内核态傻傻等等，这应该就是形成原因，画个图大概就像下面这样。

将信息告诉朋友后，朋友说他用的是 Windows 服务部署，但不管是什么模式部署，注释掉 Console.WriteLine 肯定没错。

三：总结

这次卡死的事故，主要还是开发人员大量的使用 Console.WriteLine 来输出日志，在某个时刻输出端窗口因为各种原因被他人独占，导致程序侧无法输出内容到窗口而一直被迫等待，之后朋友将日志输出切换到文件模式，问题得以解决。

其实这个问题很多新手朋友都会犯，特此记录下来。

记一次 .NET 某企业OA后端服务 卡死分析

​一、背景