Fix lock order violations: mm.mappingMu > Task.mu.

Document this ordering in mm/mm.go.

PiperOrigin-RevId: 393413203

1 files changed, 8 insertions, 1 deletions

diff --git a/pkg/sentry/kernel/task_exit.go b/pkg/sentry/kernel/task_exit.go
index 342e5debe..b3931445b 100644
--- a/pkg/sentry/kernel/task_exit.go
+++ b/pkg/sentry/kernel/task_exit.go
@@ -230,9 +230,16 @@ func (*runExitMain) execute(t *Task) taskRunState {
 	t.tg.pidns.owner.mu.Lock()
 	t.updateRSSLocked()
 	t.tg.pidns.owner.mu.Unlock()
+
+	// Release the task image resources. Accessing these fields must be
+	// done with t.mu held, but the mm.DecUsers() call must be done outside
+	// of that lock.
 	t.mu.Lock()
-	t.image.release()
+	mm := t.image.MemoryManager
+	t.image.MemoryManager = nil
+	t.image.fu = nil
 	t.mu.Unlock()
+	mm.DecUsers(t)
 
 	// Releasing the MM unblocks a blocked CLONE_VFORK parent.
 	t.unstopVforkParent()