[flang][runtime] Fix deadlock in error recovery

When an external I/O statement is in a recoverable error
state before any data transfers take place (for example,
an unformatted transfer with ERR=/IOSTAT=/IOMSG= attempted on
a formatted unit), ensure that the unit's mutex is still
released at the end of the statement.

Differential Revision: https://reviews.llvm.org/D127032

3 files changed, 14 insertions, 9 deletions

diff --git a/flang/runtime/io-api.cpp b/flang/runtime/io-api.cpp
index a50f011..b706007 100644
--- a/flang/runtime/io-api.cpp
+++ b/flang/runtime/io-api.cpp
@@ -172,7 +172,7 @@ Cookie BeginExternalListIO(
           *child, sourceFile, sourceLine);
     } else {
       return &child->BeginIoStatement<ErroneousIoStatementState>(
-          iostat, sourceFile, sourceLine);
+          iostat, nullptr /* no unit */, sourceFile, sourceLine);
     }
   } else {
     if (iostat == IostatOk && unit.access == Access::Direct) {
@@ -186,7 +186,7 @@ Cookie BeginExternalListIO(
           std::forward<A>(xs)..., unit, sourceFile, sourceLine);
     } else {
       return &unit.BeginIoStatement<ErroneousIoStatementState>(
-          iostat, sourceFile, sourceLine);
+          iostat, &unit, sourceFile, sourceLine);
     }
   }
 }
@@ -228,7 +228,7 @@ Cookie BeginExternalFormattedIO(const char *format, std::size_t formatLength,
           *child, format, formatLength, sourceFile, sourceLine);
     } else {
       return &child->BeginIoStatement<ErroneousIoStatementState>(
-          iostat, sourceFile, sourceLine);
+          iostat, nullptr /* no unit */, sourceFile, sourceLine);
     }
   } else {
     if (iostat == IostatOk) {
@@ -239,7 +239,7 @@ Cookie BeginExternalFormattedIO(const char *format, std::size_t formatLength,
           unit, format, formatLength, sourceFile, sourceLine);
     } else {
       return &unit.BeginIoStatement<ErroneousIoStatementState>(
-          iostat, sourceFile, sourceLine);
+          iostat, &unit, sourceFile, sourceLine);
     }
   }
 }
@@ -280,7 +280,7 @@ Cookie BeginUnformattedIO(
           *child, sourceFile, sourceLine);
     } else {
       return &child->BeginIoStatement<ErroneousIoStatementState>(
-          iostat, sourceFile, sourceLine);
+          iostat, nullptr /* no unit */, sourceFile, sourceLine);
     }
   } else {
     if (iostat == IostatOk) {
@@ -301,7 +301,7 @@ Cookie BeginUnformattedIO(
       return &io;
     } else {
       return &unit.BeginIoStatement<ErroneousIoStatementState>(
-          iostat, sourceFile, sourceLine);
+          iostat, &unit, sourceFile, sourceLine);
     }
   }
 }
diff --git a/flang/runtime/io-stmt.cpp b/flang/runtime/io-stmt.cpp
index c3dab05..b29ab15 100644
--- a/flang/runtime/io-stmt.cpp
+++ b/flang/runtime/io-stmt.cpp
@@ -1520,6 +1520,9 @@ bool InquireIOLengthState::Emit(const char32_t *p, std::size_t n) {
 
 int ErroneousIoStatementState::EndIoStatement() {
   SignalPendingError();
+  if (unit_) {
+    unit_->EndIoStatement();
+  }
   return IoStatementBase::EndIoStatement();
 }
 
diff --git a/flang/runtime/io-stmt.h b/flang/runtime/io-stmt.h
index 16a0e03..5a5bef5 100644
--- a/flang/runtime/io-stmt.h
+++ b/flang/runtime/io-stmt.h
@@ -711,9 +711,10 @@ private:
 
 class ErroneousIoStatementState : public IoStatementBase {
 public:
-  explicit ErroneousIoStatementState(
-      Iostat iostat, const char *sourceFile = nullptr, int sourceLine = 0)
-      : IoStatementBase{sourceFile, sourceLine} {
+  explicit ErroneousIoStatementState(Iostat iostat,
+      ExternalFileUnit *unit = nullptr, const char *sourceFile = nullptr,
+      int sourceLine = 0)
+      : IoStatementBase{sourceFile, sourceLine}, unit_{unit} {
     SetPendingError(iostat);
   }
   int EndIoStatement();
@@ -722,6 +723,7 @@ public:
 
 private:
   ConnectionState connection_;
+  ExternalFileUnit *unit_{nullptr};
 };
 
 extern template bool IoStatementState::EmitEncoded<char>(