17.windbg-!cs、~~[TID]（经典死锁）

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先上个代码，自己随手写的：

#include <windows.h >CRITICAL_SECTION cs1;CRITICAL_SECTION cs2;DWORD __stdcall thread1(LPVOID lp){EnterCriticalSection(&cs1);Sleep(10);EnterCriticalSection(&cs2);return 0;}DWORD  __stdcall thread2(LPVOID lp){EnterCriticalSection(&cs2);Sleep(10);EnterCriticalSection(&cs1);return 0;}int main(){InitializeCriticalSection(&cs1);InitializeCriticalSection(&cs2);CreateThread(NULL, 0, thread1, 0, 0, NULL);CreateThread(NULL, 0, thread2, 0, 0, NULL);system("pause");return 0;}

运行，生成release版本，去掉pdb，运行，程序停住了，windbg加载到进程，

先用~*kb查看下所有的线程堆栈:

0:003> ~*kb

   0  Id: 1a98.24c Suspend: 1 Teb: 7ffdf000 UnfrozenChildEBP RetAddr  Args to Child              0012fddc 7c92df5a 7c8025db 00000044 00000000 ntdll!KiFastSystemCallRet0012fde0 7c8025db 00000044 00000000 00000000 ntdll!NtWaitForSingleObject+0xc0012fe44 7c802542 00000044 ffffffff 00000000 kernel32!WaitForSingleObjectEx+0xa80012fe58 7854bd40 00000044 ffffffff 00000000 kernel32!WaitForSingleObject+0x120012fedc 7854c702 00000000 00392b98 00392de0 MSVCR90!_dospawn+0x1d1 [f:\dd\vctools\crt_bld\self_x86\crt\src\dospawn.c @ 215]0012ff00 7854c84b 00000000 00392b98 0012ff5c MSVCR90!comexecmd+0x60 [f:\dd\vctools\crt_bld\self_x86\crt\src\spawnve.c @ 137]0012ff38 7854cc71 00000000 00392b98 0012ff5c MSVCR90!_spawnve+0x12a [f:\dd\vctools\crt_bld\self_x86\crt\src\spawnve.c @ 273]0012ff70 004010a8 004020f4 00000001 00401218 MSVCR90!system+0x8e [f:\dd\vctools\crt_bld\self_x86\crt\src\system.c @ 87]WARNING: Stack unwind information not available. Following frames may be wrong.0012ffc0 7c817077 00300031 0032002d 7ffdc000 test2+0x10a80012fff0 00000000 00401360 00000000 78746341 kernel32!BaseProcessStart+0x23

   1  Id: 1a98.1588 Suspend: 1 Teb: 7ffde000 UnfrozenChildEBP RetAddr  Args to Child              0050ff14 7c92df5a 7c939b23 0000002c 00000000 ntdll!KiFastSystemCallRet0050ff18 7c939b23 0000002c 00000000 00000000 ntdll!NtWaitForSingleObject+0xc0050ffa0 7c921046 00403370 0040101d 00403370 ntdll!RtlpWaitForCriticalSection+0x1320050ffa8 0040101d 00403370 000203a8 7c80b729 ntdll!RtlEnterCriticalSection+0x46WARNING: Stack unwind information not available. Following frames may be wrong.0050ffec 00000000 00401000 00000000 00000000 test2+0x101d

   2  Id: 1a98.185c Suspend: 1 Teb: 7ffdd000 UnfrozenChildEBP RetAddr  Args to Child              0060ff14 7c92df5a 7c939b23 00000034 00000000 ntdll!KiFastSystemCallRet0060ff18 7c939b23 00000034 00000000 00000000 ntdll!NtWaitForSingleObject+0xc0060ffa0 7c921046 00403388 0040104d 00403388 ntdll!RtlpWaitForCriticalSection+0x1320060ffa8 0040104d 00403388 000203a8 7c80b729 ntdll!RtlEnterCriticalSection+0x46WARNING: Stack unwind information not available. Following frames may be wrong.0060ffec 00000000 00401030 00000000 00000000 test2+0x104d

#  3  Id: 1a98.159c Suspend: 1 Teb: 7ffdb000 UnfrozenChildEBP RetAddr  Args to Child              003dffc8 7c972119 00000005 00000004 00000001 ntdll!DbgBreakPoint003dfff4 00000000 00000000 00000000 00000000 ntdll!DbgUiRemoteBreakin+0x2d

我们注意到1号线程的线程堆栈是从ntdll!RtlEnterCriticalSection中开始的，那么ntdll!RtlEnterCriticalSection又是什么函数的入口呢，首先猜到的是EnterCriticalSection,这个函数是kernel32.dll中的，为了验证猜测，我们用dump查看到kernel32.dll的导出函数：

果然如此，

!cs

!cs 扩展显示一个或多个临界区(critical section)或者整个临界区树

前面说的ntdll!RtlEnterCriticalSection的第一个参数是临界区的地址，事实上用uf反汇编它，可以看到是ret 4，说明就只有一个参数

那么，

!cs Address 指定要显示的临界区地址。如果省略该参数，调试器显示当前进程中所有临界区。

0:003> ~1kbChildEBP RetAddr  Args to Child              0050ff14 7c92df5a 7c939b23 0000002c 00000000 ntdll!KiFastSystemCallRet0050ff18 7c939b23 0000002c 00000000 00000000 ntdll!NtWaitForSingleObject+0xc0050ffa0 7c921046 00403370 0040101d 00403370 ntdll!RtlpWaitForCriticalSection+0x1320050ffa8 0040101d 00403370 000203a8 7c80b729 ntdll!RtlEnterCriticalSection+0x46WARNING: Stack unwind information not available. Following frames may be wrong.0050ffec 00000000 00401000 00000000 00000000 test2+0x101d0:003> !cs 00403370 -----------------------------------------Critical section   = 0x00403370 (test2+0x3370)DebugInfo          = 0x7c99e9e0LOCKEDLockCount          = 0x1OwningThread       = 0x0000185cRecursionCount     = 0x1LockSemaphore      = 0x2CSpinCount          = 0x00000000

这里LockCount为1意思为除了一个线程拥有它外，另外还有一个线程在等待它，它是由EnterCriticalSection增加，LeaveCriticalSection来减小的,比如我再加一点代码:

DWORD  __stdcall thread3(LPVOID lp){EnterCriticalSection(&cs2);Sleep(10);EnterCriticalSection(&cs1);return 0;}int main(){InitializeCriticalSection(&cs1);InitializeCriticalSection(&cs2);CreateThread(NULL, 0, thread1, 0, 0, NULL);CreateThread(NULL, 0, thread2, 0, 0, NULL);CreateThread(NULL, 0, thread3, 0, 0, NULL);system("pause");return 0;}

这时运行windbg：

0:004> ~1kbChildEBP RetAddr  Args to Child              0051fe48 7c92df5a 7c939b23 00000034 00000000 ntdll!KiFastSystemCallRet0051fe4c 7c939b23 00000034 00000000 00000000 ntdll!NtWaitForSingleObject+0xc0051fed4 7c921046 00417140 00411420 00417140 ntdll!RtlpWaitForCriticalSection+0x132*** WARNING: Unable to verify checksum for D:\Project1\test2\Debug\test2.exe0051fedc 00411420 00417140 00000000 00000000 ntdll!RtlEnterCriticalSection+0x460051ffb4 7c80b729 00000000 00000000 00000000 test2!thread1+0x50 [d:\project1\test2\test2\test2.cpp @ 10]0051ffec 00000000 00411122 00000000 00000000 kernel32!BaseThreadStart+0x370:004> !cs 00417140-----------------------------------------Critical section   = 0x00417140 (test2!cs2+0x0)DebugInfo          = 0x7c99ea00LOCKEDLockCount          = 0x2OwningThread       = 0x00001f60RecursionCount     = 0x1LockSemaphore      = 0x34SpinCount          = 0x00000000

可以发现LockCount变成了2，如果临界区是有信号的，则显示NOT LOCKED(值为-1)

OwningThread表示拥有这个临界区的线程ID,RecursionCount表示拥有线程调了几次EnterCriticalSection，这其实也影响到了LockCount,如果拥有线程多调用一次EnterCriticalSection,那么 LockCount也会相应加1，因为LockCount标识了任意线程调用EnterCriticalSection请求这个互斥量的次数减1,(所以0-1=-1为NOT LOCKED)当然，前面如果调用了LeaveCriticalSection,那么 LockCount也会相应减1

我们继续看原有的程序：

~~[TID]线程 ID 为 TID 的线程。（中括号是必需的，而且在第二个~和左括号间不能有空格）

0:003> ~~[0x0000185c]   2  Id: 1a98.185c Suspend: 1 Teb: 7ffdd000 Unfrozen      Start: test2+0x1030 (00401030)       Priority: 0  Priority class: 32  Affinity: f

这意思就是1号线程等待的临界区拥有者是2号线程，那么同样我们对2号线程进行分析:

0:003> ~2kbChildEBP RetAddr  Args to Child              0060ff14 7c92df5a 7c939b23 00000034 00000000 ntdll!KiFastSystemCallRet0060ff18 7c939b23 00000034 00000000 00000000 ntdll!NtWaitForSingleObject+0xc0060ffa0 7c921046 00403388 0040104d 00403388 ntdll!RtlpWaitForCriticalSection+0x1320060ffa8 0040104d 00403388 000203a8 7c80b729 ntdll!RtlEnterCriticalSection+0x46WARNING: Stack unwind information not available. Following frames may be wrong.0060ffec 00000000 00401030 00000000 00000000 test2+0x104d0:003> !cs 00403388 -----------------------------------------Critical section   = 0x00403388 (test2+0x3388)DebugInfo          = 0x7c99e9c0LOCKEDLockCount          = 0x1OwningThread       = 0x00001588RecursionCount     = 0x1LockSemaphore      = 0x34SpinCount          = 0x000000000:003> ~~[0x00001588]   1  Id: 1a98.1588 Suspend: 1 Teb: 7ffde000 Unfrozen      Start: test2+0x1000 (00401000)       Priority: 0  Priority class: 32  Affinity: f

原来2号线程等待的临界区拥有者是1号线程，所以经典的死锁现象出现了！！！！！！！！！！！！！！！！！！！！！！！！

下面继续介绍下!cs的扩展:

!cs -s 如果可能的话，显示每个临界区的初始堆栈回溯。

!cs -l 仅显示锁定的临界区。

0:003> !cs -l -----------------------------------------DebugInfo          = 0x7c99e9c0Critical section   = 0x00403388 (test2+0x3388)LOCKEDLockCount          = 0x1OwningThread       = 0x00001588RecursionCount     = 0x1LockSemaphore      = 0x34SpinCount          = 0x00000000-----------------------------------------DebugInfo          = 0x7c99e9e0Critical section   = 0x00403370 (test2+0x3370)LOCKEDLockCount          = 0x1OwningThread       = 0x0000185cRecursionCount     = 0x1LockSemaphore      = 0x2CSpinCount          = 0x00000000

!cs starAddress EndAddress指定要搜索临界区的地址范围

0:003> !cs 0x00400000 0x00500000-----------------------------------------DebugInfo          = 0x7c99e9c0Critical section   = 0x00403388 (test2+0x3388)LOCKEDLockCount          = 0x1OwningThread       = 0x00001588RecursionCount     = 0x1LockSemaphore      = 0x34SpinCount          = 0x00000000-----------------------------------------DebugInfo          = 0x7c99e9e0Critical section   = 0x00403370 (test2+0x3370)LOCKEDLockCount          = 0x1OwningThread       = 0x0000185cRecursionCount     = 0x1LockSemaphore      = 0x2CSpinCount          = 0x00000000

!cs -o 对所有显示出来的已锁定的临界区，显示所有者的堆栈。
!cs -?显示该命令的帮助文本。

0:003> !cs -?!cs [-s] [-l] [-o]                   - dump all the active critical sections in the current process.!cs [-s] [-o] address                - dump critical section at this address.!cs [-s] [-l] [-o] address1 address2 - dump all the active critical sections in this range.!cs [-s] [-o] -d address             - dump critical section corresponding to DebugInfo at this address."-s" will dump the critical section initialization stack trace if it is available."-l" will dump only the locked critical sections."-o" will dump the critical section owner's stack.