From d57ba73e962955d928a72d7fa23a90b3dbb6e50c Mon Sep 17 00:00:00 2001
From: Zebediah Figura <z.figura12@gmail.com>
Date: Tue, 29 Jan 2019 21:39:05 -0600
Subject: [PATCH 04/13] ntoskrnl.exe: Implement
 ExAcquireSharedStarveExclusive().

Signed-off-by: Zebediah Figura <z.figura12@gmail.com>
---
 dlls/ntoskrnl.exe/ntoskrnl.exe.spec |  2 +-
 dlls/ntoskrnl.exe/sync.c            | 61 +++++++++++++++++++++++++++++
 include/ddk/wdm.h                   |  1 +
 3 files changed, 63 insertions(+), 1 deletion(-)

diff --git a/dlls/ntoskrnl.exe/ntoskrnl.exe.spec b/dlls/ntoskrnl.exe/ntoskrnl.exe.spec
index 217f27ff..4609c86d 100644
--- a/dlls/ntoskrnl.exe/ntoskrnl.exe.spec
+++ b/dlls/ntoskrnl.exe/ntoskrnl.exe.spec
@@ -122,7 +122,7 @@
 @ stub DbgSetDebugFilterState
 @ stdcall ExAcquireResourceExclusiveLite(ptr long)
 @ stdcall ExAcquireResourceSharedLite(ptr long)
-@ stub ExAcquireSharedStarveExclusive
+@ stdcall ExAcquireSharedStarveExclusive(ptr long)
 @ stub ExAcquireSharedWaitForExclusive
 @ stub ExAllocateFromPagedLookasideList
 @ stdcall ExAllocatePool(long long)
diff --git a/dlls/ntoskrnl.exe/sync.c b/dlls/ntoskrnl.exe/sync.c
index b37a46e4..3033c8a2 100644
--- a/dlls/ntoskrnl.exe/sync.c
+++ b/dlls/ntoskrnl.exe/sync.c
@@ -825,3 +825,64 @@ BOOLEAN WINAPI ExAcquireResourceSharedLite( ERESOURCE *resource, BOOLEAN wait )
 
     return TRUE;
 }
+
+/***********************************************************************
+ *           ExAcquireSharedStarveExclusive  (NTOSKRNL.EXE.@)
+ */
+BOOLEAN WINAPI ExAcquireSharedStarveExclusive( ERESOURCE *resource, BOOLEAN wait )
+{
+    OWNER_ENTRY *entry;
+    KIRQL irql;
+
+    TRACE("resource %p, wait %u.\n", resource, wait);
+
+    KeAcquireSpinLock( &resource->SpinLock, &irql );
+
+    entry = resource_get_shared_entry( resource, (ERESOURCE_THREAD)KeGetCurrentThread() );
+
+    if (resource->Flag & ResourceOwnedExclusive)
+    {
+        if (resource->OwnerEntry.OwnerThread == (ERESOURCE_THREAD)KeGetCurrentThread())
+        {
+            resource->ActiveEntries++;
+            KeReleaseSpinLock( &resource->SpinLock, irql );
+            return TRUE;
+        }
+    }
+    else if (resource->ActiveEntries || !resource->NumberOfExclusiveWaiters)
+    {
+        /* We are starving exclusive waiters, but we cannot steal the resource
+         * out from under an exclusive waiter who is about to acquire it. */
+        entry->OwnerCount++;
+        resource->ActiveEntries++;
+        KeReleaseSpinLock( &resource->SpinLock, irql );
+        return TRUE;
+    }
+
+    if (!wait)
+    {
+        KeReleaseSpinLock( &resource->SpinLock, irql );
+        return FALSE;
+    }
+
+    if (!resource->SharedWaiters)
+    {
+        resource->SharedWaiters = heap_alloc( sizeof(*resource->SharedWaiters) );
+        KeInitializeSemaphore( resource->SharedWaiters, 0, INT_MAX );
+    }
+    resource->NumberOfSharedWaiters++;
+
+    KeReleaseSpinLock( &resource->SpinLock, irql );
+
+    KeWaitForSingleObject( resource->SharedWaiters, Executive, KernelMode, FALSE, NULL );
+
+    KeAcquireSpinLock( &resource->SpinLock, &irql );
+
+    entry->OwnerCount++;
+    resource->ActiveEntries++;
+    resource->NumberOfSharedWaiters--;
+
+    KeReleaseSpinLock( &resource->SpinLock, irql );
+
+    return TRUE;
+}
diff --git a/include/ddk/wdm.h b/include/ddk/wdm.h
index 14d4ba4e..a65974da 100644
--- a/include/ddk/wdm.h
+++ b/include/ddk/wdm.h
@@ -1514,6 +1514,7 @@ NTSTATUS  WINAPI DbgQueryDebugFilterState(ULONG, ULONG);
 void      WINAPI ExAcquireFastMutexUnsafe(PFAST_MUTEX);
 BOOLEAN   WINAPI ExAcquireResourceExclusiveLite(ERESOURCE*,BOOLEAN);
 BOOLEAN   WINAPI ExAcquireResourceSharedLite(ERESOURCE*,BOOLEAN);
+BOOLEAN   WINAPI ExAcquireSharedStarveExclusive(ERESOURCE*,BOOLEAN);
 PVOID     WINAPI ExAllocatePool(POOL_TYPE,SIZE_T);
 PVOID     WINAPI ExAllocatePoolWithQuota(POOL_TYPE,SIZE_T);
 PVOID     WINAPI ExAllocatePoolWithTag(POOL_TYPE,SIZE_T,ULONG);
-- 
2.20.1