1 files changed, 7 insertions, 0 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 380c1bafe75c..cbf4a12aab4d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -364,6 +364,13 @@ static int copy_mm(unsigned long clone_flags, struct task_struct * tsk)
 	if (clone_flags & CLONE_VM) {
 		atomic_inc(&oldmm->mm_users);
 		mm = oldmm;
+		/*
+		 * There are cases where the PTL is held to ensure no
+		 * new threads start up in user mode using an mm, which
+		 * allows optimizing out ipis; the tlb_gather_mmu code
+		 * is an example.
+		 */
+		spin_unlock_wait(&oldmm->page_table_lock);
 		goto good_mm;
 	}