[PATCH] user32: Load libpng in DllMain.

[Tim Clem]

libpng is currently loaded on the first attempt to access a PNG icon
or cursor. That creates a race condition that can deadlock the
loader in certain circumstances if LoadIcon or LoadCursor is called
while while the loader lock is held, e.g. from a DllMain.

Signed-off-by: Tim Clem <tclem at codeweavers.com>
---
It's possible for one thread to win the INIT_ONCE to load libpng
without owning the loader lock. If the thread with the loader lock
happens to try to load libpng shortly thereafter, they deadlock.

All of Wine's built-in icon resources are PNGs, so we almost always
end up loading libpng anyway. Doing it up-front in user32's DllMain
ensures that it's done while the loader lock is held and prevents
the issue.

 dlls/user32/cursoricon.c   | 21 +++------------------
 dlls/user32/png.c          |  4 ++--
 dlls/user32/user_main.c    |  6 +++++-
 dlls/user32/user_private.h |  3 +++
 4 files changed, 13 insertions(+), 21 deletions(-)

diff --git a/dlls/user32/cursoricon.c b/dlls/user32/cursoricon.c
index 7ad0a04a551..dc831db9287 100644
--- a/dlls/user32/cursoricon.c
+++ b/dlls/user32/cursoricon.c
@@ -111,21 +111,6 @@ static int get_display_bpp(void)
     return ret;
 }
 
-static INIT_ONCE init_once = INIT_ONCE_STATIC_INIT;
-
-static const struct png_funcs *png_funcs;
-
-static BOOL WINAPI load_libpng( INIT_ONCE *once, void *param, void **context )
-{
-    __wine_init_unix_lib( user32_module, DLL_PROCESS_ATTACH, NULL, &png_funcs );
-    return TRUE;
-}
-
-static BOOL have_libpng(void)
-{
-    return InitOnceExecuteOnce( &init_once, load_libpng, NULL, NULL ) && png_funcs;
-}
-
 static HICON alloc_icon_handle( BOOL is_ani, UINT num_steps )
 {
     struct cursoricon_object *obj;
@@ -571,7 +556,7 @@ static BOOL CURSORICON_GetResIconEntry( LPCVOID dir, DWORD size, int n,
     *width = icon->bWidth;
     *height = icon->bHeight;
     *bits = resdir->idEntries[n].wBitCount;
-    if (!*width && !*height && have_libpng()) *width = *height = 256;
+    if (!*width && !*height && png_funcs) *width = *height = 256;
     return TRUE;
 }
 
@@ -704,7 +689,7 @@ static BOOL CURSORICON_GetFileEntry( LPCVOID dir, DWORD size, int n,
 
     if (info->biSize == PNG_SIGN)
     {
-        if (have_libpng()) return png_funcs->get_png_info(info, size, width, height, bits);
+        if (png_funcs) return png_funcs->get_png_info(info, size, width, height, bits);
         *width = *height = *bits = 0;
         return TRUE;
     }
@@ -858,7 +843,7 @@ static HICON create_icon_from_bmi( const BITMAPINFO *bmi, DWORD maxsize, HMODULE
     {
         BITMAPINFO *bmi_png;
 
-        if (!have_libpng()) return 0;
+        if (!png_funcs) return 0;
         bmi_png = png_funcs->load_png( (const char *)bmi, &maxsize );
         if (bmi_png)
         {
diff --git a/dlls/user32/png.c b/dlls/user32/png.c
index a994c6de5c2..bcd619fe52b 100644
--- a/dlls/user32/png.c
+++ b/dlls/user32/png.c
@@ -293,7 +293,7 @@ static BITMAPINFO * CDECL load_png(const char *png_data, DWORD *size)
     return info;
 }
 
-static const struct png_funcs png_funcs =
+static const struct png_funcs funcs =
 {
     get_png_info,
     load_png
@@ -335,7 +335,7 @@ NTSTATUS CDECL __wine_init_unix_lib( HMODULE module, DWORD reason, const void *p
     LOAD_FUNCPTR(png_set_read_fn);
 #undef LOAD_FUNCPTR
 
-    *(const struct png_funcs **)ptr_out = &png_funcs;
+    *(const struct png_funcs **)ptr_out = &funcs;
     return STATUS_SUCCESS;
 }
 
diff --git a/dlls/user32/user_main.c b/dlls/user32/user_main.c
index 303f19accfc..882a0c5237b 100644
--- a/dlls/user32/user_main.c
+++ b/dlls/user32/user_main.c
@@ -52,6 +52,8 @@ static HPALETTE hPrimaryPalette;
 
 static DWORD exiting_thread_id;
 
+const struct png_funcs *png_funcs = NULL;
+
 extern void WDML_NotifyThreadDetach(void);
 
 #ifdef __MINGW32__
@@ -382,8 +384,10 @@ BOOL WINAPI DllMain( HINSTANCE inst, DWORD reason, LPVOID reserved )
     case DLL_PROCESS_ATTACH:
         user32_module = inst;
         ret = process_attach();
-        if(ret)
+        if(ret) {
             imm32_module = LoadLibraryW(L"imm32.dll");
+            __wine_init_unix_lib( user32_module, DLL_PROCESS_ATTACH, NULL, &png_funcs );
+        }
         break;
     case DLL_THREAD_DETACH:
         thread_detach();
diff --git a/dlls/user32/user_private.h b/dlls/user32/user_private.h
index 7c4d9015976..0be02919bbe 100644
--- a/dlls/user32/user_private.h
+++ b/dlls/user32/user_private.h
@@ -380,6 +380,9 @@ struct png_funcs
     BITMAPINFO * (CDECL *load_png)(const char *png_data, DWORD *size);
 };
 
+/* May be NULL if libpng cannot be loaded. */
+extern const struct png_funcs *png_funcs DECLSPEC_HIDDEN;
+
 /* Mingw's assert() imports MessageBoxA and gets confused by user32 exporting it */
 #ifdef __MINGW32__
 #undef assert
-- 
2.32.0