Fix a mutex abandon case with WaitHandle.WaitAll in the PAL (#25452)

Fixes https://github.com/dotnet/coreclr/issues/25108
- Upon a `WaitAll` when all waits are already satisfied, the abandoned flag is overwritten with the abandoned state of the last wait object in the array
- So if the first wait object is an abandoned mutex and the second wait object is a signaled event, the `WaitAll` succeeds and does not report that anything was abandoned
- Fixed to accumulate into the flag instead of overwriting it

1 files changed, 6 insertions, 2 deletions

diff --git a/src/pal/src/synchmgr/wait.cpp b/src/pal/src/synchmgr/wait.cpp
index 31153ae02b..1f20ba23bf 100644
--- a/src/pal/src/synchmgr/wait.cpp
+++ b/src/pal/src/synchmgr/wait.cpp
@@ -531,8 +531,8 @@ DWORD CorUnix::InternalWaitForMultipleObjectsEx(
     iSignaledObjIndex = -1;
     for (i=0;i<(int)nCount;i++)
     {
-        bool fValue;
-        palErr = ppISyncWaitCtrlrs[i]->CanThreadWaitWithoutBlocking(&fValue, &fAbandoned);
+        bool fValue, fWaitObjectAbandoned = false;
+        palErr = ppISyncWaitCtrlrs[i]->CanThreadWaitWithoutBlocking(&fValue, &fWaitObjectAbandoned);
         if (NO_ERROR != palErr)
         {
             ERROR("ISynchWaitController::CanThreadWaitWithoutBlocking() failed for "
@@ -540,6 +540,10 @@ DWORD CorUnix::InternalWaitForMultipleObjectsEx(
             pThread->SetLastError(ERROR_INTERNAL_ERROR);
             goto WFMOExIntReleaseControllers;            
         }
+        if (fWaitObjectAbandoned)
+        {
+            fAbandoned = true;
+        }
         if (fValue)
         {
             iSignaledObjCount++;