From: Jinoh Kang jinoh.kang.kr@gmail.com
Ensure proper atomic update, so that other threads do not read stale information from IO_STATUS_BLOCK. --- dlls/ntdll/unix/unix_private.h | 25 ++++++++++++++++++++++--- 1 file changed, 22 insertions(+), 3 deletions(-)
diff --git a/dlls/ntdll/unix/unix_private.h b/dlls/ntdll/unix/unix_private.h index 47f0f9c56a9..3939186ad05 100644 --- a/dlls/ntdll/unix/unix_private.h +++ b/dlls/ntdll/unix/unix_private.h @@ -361,6 +361,8 @@ static inline BOOL in_wow64_call(void)
static inline void set_async_iosb( client_ptr_t iosb, NTSTATUS status, ULONG_PTR info ) { + NTSTATUS *status_ptr; + if (!iosb) return;
if (in_wow64_call()) @@ -370,19 +372,36 @@ static inline void set_async_iosb( client_ptr_t iosb, NTSTATUS status, ULONG_PTR NTSTATUS Status; ULONG Information; } *io = wine_server_get_ptr( iosb ); - io->Status = status; + status_ptr = &io->Status; io->Information = info; } else { IO_STATUS_BLOCK *io = wine_server_get_ptr( iosb ); #ifdef NONAMELESSUNION - io->u.Status = status; + status_ptr = &io->u.Status; #else - io->Status = status; + status_ptr = &io->Status; #endif io->Information = info; } + + /* GetOverlappedResultEx() skips waiting for the event/file handle if the + * Status field indicates completion, and returns the result from the + * Information field. + * + * Hence, we have to ensure that writes to the Information field are seen + * from the other threads *before* writes to the Status field. + * + * Otherwise, a race condition results: if writing the Status field has + * been completed but the subsequent update to the Information field has + * not, the application may end up reading stale value from it. + * + * The race condition can be especially problematic with applications that + * use the HasOverlappedIoCompleted() macro in a tight loop to poll for + * completion of overlapped I/O. + */ + WriteRelease( (volatile LONG *)status_ptr, status ); }
static inline client_ptr_t iosb_client_ptr( IO_STATUS_BLOCK *io )