Fix thread-safety comments for log rolling/reseating methods

Author: JosiahWI

include/tscore/DiagsTypes.h

@@ -470,9 +470,11 @@ class Diags : public DebugInterface
   ///       path. The old file descriptor is closed.
   ///       On failure to reopen: diags_log is unchanged; the old descriptor
   ///       remains in use.
-  /// @note Thread-safe. The current log is flushed and the new file is opened
-  ///       outside the internal lock; only the pointer swap is performed
-  ///       under the lock. Safe to call while concurrent logging is active.
+  /// @note Not concurrency-safe with respect to should_roll_diagslog().
+  ///       Reads diags_log outside the internal lock before acquiring it for
+  ///       the pointer swap. Callers must ensure reseat and roll operations
+  ///       are externally serialized. Concurrent logging via print_va() is
+  ///       safe because print_va() holds the internal lock for all accesses.
   bool reseat_diagslog();
 
   /// @brief Checks rolling conditions and rolls the diagnostics log if due.
@@ -483,8 +485,11 @@ class Diags : public DebugInterface
   ///
   /// @return true if the log was rolled. false if no rolling was needed,
   ///         or if diags_log is nullptr or uninitialized.
-  /// @note Thread-safe. File operations (stat, flush, roll) occur outside the
-  ///       internal lock; only the pointer swap is performed under the lock.
+  /// @note Not concurrency-safe with respect to reseat_diagslog().
+  ///       Reads diags_log outside the internal lock before acquiring it for
+  ///       the pointer swap. Callers must ensure roll and reseat operations
+  ///       are externally serialized. Concurrent logging via print_va() is
+  ///       safe because print_va() holds the internal lock for all accesses.
   bool should_roll_diagslog();
 
   /// @brief Checks rolling conditions and rolls stdout/stderr output logs if due.
@@ -493,7 +498,10 @@ class Diags : public DebugInterface
   /// the same file, both pointers are updated atomically.
   ///
   /// @return true if any output log was rolled. false otherwise.
-  /// @note Thread-safe. Pointer swaps are performed under the internal lock.
+  /// @note Pointer swaps are performed under the internal lock via
+  ///       set_std_output(). File inspection (fstat, fflush) occurs outside
+  ///       the lock. Callers must ensure no concurrent set_std_output() or
+  ///       reseat_diagslog() call is in progress.
   bool should_roll_outputlog();
 
   /// @brief Redirects stdout or stderr to the specified file.
@@ -511,8 +519,11 @@ class Diags : public DebugInterface
   ///       and the corresponding log pointer (stdout_log or stderr_log) is
   ///       updated to the new handle.
   ///       On failure: the log pointer is nullptr and the redirect did not occur.
-  /// @note Thread-safe. The pointer swap and dup2() call are performed under
-  ///       the internal lock.
+  /// @note The pointer swap and dup2() call are performed under the internal
+  ///       lock. However, the old pointer snapshot is read outside the lock,
+  ///       so this method is not concurrency-safe with respect to concurrent
+  ///       calls to itself or should_roll_outputlog(). Callers must ensure
+  ///       these operations are externally serialized.
   bool set_std_output(StdStream stream, const char *file);
 
   /// The debug tag pattern passed at construction time. May be nullptr if no