[PATCH v2 6/7] ntdll: Use shared loader locking in LdrQueryProcessModuleInformation().

[Paul Gofman]

Signed-off-by: Paul Gofman 
---
 dlls/ntdll/loader.c | 37 ++++++++++++++++++++++++++++++++++---
 1 file changed, 34 insertions(+), 3 deletions(-)

diff --git a/dlls/ntdll/loader.c b/dlls/ntdll/loader.c
index 9cadd32f1de..84b3592abb8 100644
--- a/dlls/ntdll/loader.c
+++ b/dlls/ntdll/loader.c
@@ -161,6 +161,7 @@ static RTL_CRITICAL_SECTION_DEBUG critsect_debug =
 static RTL_CRITICAL_SECTION loader_section = { &critsect_debug, -1, 0, 0, 0, 0 };

static RTL_SRWLOCK loader_srw_lock = RTL_SRWLOCK_INIT;
+static volatile BOOL locked_exclusive;

static CRITICAL_SECTION dlldir_section;
 static CRITICAL_SECTION_DEBUG dlldir_critsect_debug =
@@ -250,8 +251,32 @@ static void lock_loader_exclusive(void)
     ULONG recursion_count = inc_recursion_count();

TRACE( "recursion_count %u.\n", recursion_count );
+    if (!recursion_count)
+    {
+        if (!RtlDllShutdownInProgress())
+            RtlAcquireSRWLockExclusive( &loader_srw_lock );
+        locked_exclusive = TRUE;
+    }
+    else
+    {
+        assert( locked_exclusive );
+    }
+}
+
+/*************************************************************************
+ *		lock_loader_shared
+ *
+ * Take shared ownership of internal loader lock.
+ * If the thread already has exclusive lock it will stay exclusive.
+ */
+static void lock_loader_shared(void)
+{
+    ULONG recursion_count = inc_recursion_count();
+
+    TRACE("recursion_count %u, locked_exclusive %d.\n", recursion_count, locked_exclusive);
+
     if (!recursion_count && !RtlDllShutdownInProgress())
-        RtlAcquireSRWLockExclusive( &loader_srw_lock );
+        RtlAcquireSRWLockShared( &loader_srw_lock );
 }

/*************************************************************************
@@ -269,8 +294,14 @@ static void unlock_loader(void)

assert( recursion_count != ~0u );

-    if (!recursion_count)
+    if (recursion_count) return;
+
+    if (locked_exclusive)
+    {
+        locked_exclusive = FALSE;
         RtlReleaseSRWLockExclusive( &loader_srw_lock );
+    }
+    else RtlReleaseSRWLockShared( &loader_srw_lock );
 }

#define RTL_UNLOAD_EVENT_TRACE_NUMBER 64
@@ -3283,7 +3314,7 @@ NTSTATUS WINAPI LdrQueryProcessModuleInformation(RTL_PROCESS_MODULES *smi,

smi->ModulesCount = 0;

-    lock_loader_exclusive();
+    lock_loader_shared();
     mark = &NtCurrentTeb()->Peb->LdrData->InLoadOrderModuleList;
     for (entry = mark->Flink; entry != mark; entry = entry->Flink)
     {