libio: Fix deadlock in location management

Perform a context-dependent deferred location release to avoid a
deadlock on the file system instance locks, for example during a
chdir().

Update #2936.

cpukit/libcsupport/include/rtems/libio_.h

@@ -507,11 +507,14 @@ rtems_filesystem_global_location_t *rtems_filesystem_global_location_obtain(
  * deferred.  The next obtain call will do the actual release.
  *
  * @param[in] global_loc The global file system location.  It must not be NULL.
+ * @param[in] deferred If true, then do a deferred release, otherwise release
+ *   it immediately.
  *
  * @see rtems_filesystem_global_location_obtain().
  */
 void rtems_filesystem_global_location_release(
-  rtems_filesystem_global_location_t *global_loc
+  rtems_filesystem_global_location_t *global_loc,
+  bool deferred
 );
 
 void rtems_filesystem_location_detach(

cpukit/libcsupport/src/chdir.c

@@ -39,7 +39,7 @@ int rtems_filesystem_chdir( rtems_filesystem_location_info_t *loc )
     );
   } else {
     rtems_filesystem_location_error( &global_loc->location, ENOTDIR );
-    rtems_filesystem_global_location_release( global_loc );
+    rtems_filesystem_global_location_release( global_loc, true );
     rv = -1;
   }
 

cpukit/libcsupport/src/chroot.c

@@ -80,7 +80,7 @@ int chroot( const char *path )
     }
 
     if ( rv != 0 ) {
-      rtems_filesystem_global_location_release( new_root_loc );
+      rtems_filesystem_global_location_release( new_root_loc, true );
     }
   } else {
     rv = -1;
@@ -89,7 +89,7 @@ int chroot( const char *path )
   rtems_filesystem_eval_path_cleanup( &ctx );
 
   if ( rv != 0 ) {
-    rtems_filesystem_global_location_release( new_current_loc );
+    rtems_filesystem_global_location_release( new_current_loc, false );
   }
 
   return rv;

cpukit/libcsupport/src/mount.c

@@ -126,7 +126,7 @@ static int register_subordinate_file_system(
       );
       rtems_filesystem_mt_unlock();
     } else {
-      rtems_filesystem_global_location_release( mt_point_node );
+      rtems_filesystem_global_location_release( mt_point_node, true );
     }
   } else {
     rtems_filesystem_eval_path_error( &ctx, EBUSY );

cpukit/libcsupport/src/privateenv.c

@@ -44,8 +44,8 @@ void rtems_libio_free_user_env(void *arg)
   bool uses_global_env = env == &rtems_global_user_env;
 
   if (!uses_global_env) {
-    rtems_filesystem_global_location_release(env->current_directory);
-    rtems_filesystem_global_location_release(env->root_directory);
+    rtems_filesystem_global_location_release(env->current_directory, false);
+    rtems_filesystem_global_location_release(env->root_directory, false);
     free(env);
   }
 }

cpukit/libcsupport/src/sup_fs_eval_path.c

@@ -301,8 +301,8 @@ void rtems_filesystem_eval_path_cleanup(
 {
   free_location(&ctx->currentloc);
   rtems_filesystem_instance_unlock(&ctx->startloc->location);
-  rtems_filesystem_global_location_release(ctx->startloc);
-  rtems_filesystem_global_location_release(ctx->rootloc);
+  rtems_filesystem_global_location_release(ctx->startloc, false);
+  rtems_filesystem_global_location_release(ctx->rootloc, false);
 }
 
 void rtems_filesystem_eval_path_cleanup_with_parent(

cpukit/libcsupport/src/sup_fs_location.c

@@ -106,7 +106,7 @@ void rtems_filesystem_global_location_assign(
   *lhs_global_loc_ptr = rhs_global_loc;
   rtems_filesystem_mt_entry_unlock(lock_context);
 
-  rtems_filesystem_global_location_release(lhs_global_loc);
+  rtems_filesystem_global_location_release(lhs_global_loc, true);
 }
 
 static void release_with_count(
@@ -184,10 +184,11 @@ rtems_filesystem_global_location_t *rtems_filesystem_global_location_obtain(
 }
 
 void rtems_filesystem_global_location_release(
-  rtems_filesystem_global_location_t *global_loc
+  rtems_filesystem_global_location_t *global_loc,
+  bool deferred
 )
 {
-  if (_Thread_Dispatch_is_enabled()) {
+  if (!deferred) {
     release_with_count(global_loc, 1);
   } else {
     rtems_interrupt_lock_context lock_context;
@@ -233,7 +234,7 @@ void rtems_filesystem_do_unmount(
   rtems_filesystem_mt_lock();
   rtems_chain_extract_unprotected(&mt_entry->mt_node);
   rtems_filesystem_mt_unlock();
-  rtems_filesystem_global_location_release(mt_entry->mt_point_node);
+  rtems_filesystem_global_location_release(mt_entry->mt_point_node, false);
   (*mt_entry->ops->fsunmount_me_h)(mt_entry);
 
   if (mt_entry->unmount_task != 0) {

testsuites/fstests/fsnofs01/init.c

@@ -74,9 +74,9 @@ static void test_initial_values(void)
   rtems_test_assert(null_mt->mt_fs_root == null_loc);
   rtems_test_assert(!null_mt->mounted);
   rtems_test_assert(!null_mt->writeable);
-  rtems_test_assert(null_loc->reference_count == 6);
+  rtems_test_assert(null_loc->reference_count == 4);
   rtems_test_assert(null_loc->deferred_released_next == NULL);
-  rtems_test_assert(null_loc->deferred_released_count == 2);
+  rtems_test_assert(null_loc->deferred_released_count == 0);
 }
 
 static void test_location_obtain(void)
@@ -90,7 +90,7 @@ static void test_location_obtain(void)
   rtems_test_assert(node_count(loc_chain) == 1);
   rtems_test_assert(null_loc->reference_count == 5);
 
-  rtems_filesystem_global_location_release(null_loc);
+  rtems_filesystem_global_location_release(null_loc, false);
 
   rtems_test_assert(node_count(loc_chain) == 1);
   rtems_test_assert(null_loc->reference_count == 4);
@@ -106,7 +106,7 @@ static void test_null_location_obtain(void)
   rtems_test_assert(node_count(loc_chain) == 1);
   rtems_test_assert(null_loc->reference_count == 5);
 
-  rtems_filesystem_global_location_release(null_loc);
+  rtems_filesystem_global_location_release(null_loc, false);
 
   rtems_test_assert(node_count(loc_chain) == 1);
   rtems_test_assert(null_loc->reference_count == 4);