Add an additional assert() verifying mutex invariants on the

unixShmSystemLock() routine in the unix VFS.

FossilOrigin-Name: cb1511065d5348c5b3015dc9d690fc5d519a14ffdfa7164bb552a4fa686ad142

manifest

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-D 2018-10-02T19:58:08.325
+C Add\san\sadditional\sassert()\sverifying\smutex\sinvariants\son\sthe\nunixShmSystemLock()\sroutine\sin\sthe\sunix\sVFS.
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@@ -487,7 +487,7 @@ F src/os.c 8aeb0b0f40f8f5b0da03fe49706695adaf42d2f516ab95abc72e86c245e119de
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-F src/os_unix.c fd755a51cc621b14c6b5816912e8e103ccc28c46d64f8173f22ba992ddbe9fd3
+F src/os_unix.c d483d738183c822cc96ec5539424eee5b9847c882dee57f93b880aaf46a7af19
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manifest.uuid

@@ -1 +1 @@
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+cb1511065d5348c5b3015dc9d690fc5d519a14ffdfa7164bb552a4fa686ad142

src/os_unix.c

@@ -4288,6 +4288,7 @@ static int unixShmSystemLock(
   /* Access to the unixShmNode object is serialized by the caller */
   pShmNode = pFile->pInode->pShmNode;
   assert( pShmNode->nRef==0 || sqlite3_mutex_held(pShmNode->pShmMutex) );
+  assert( pShmNode->nRef>0 || unixMutexHeld() );
 
   /* Shared locks never span more than one byte */
   assert( n==1 || lockType!=F_RDLCK );