[PATCH v6 11/16] mm: enforce vma to be in detached state before freeing

[Suren Baghdasaryan <surenb@google.com>]

exit_mmap() frees vmas without detaching them. This will become a problem
when we introduce vma reuse. Ensure that vmas are always detached before
being freed.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 kernel/fork.c |  4 ++++
 mm/vma.c      | 10 ++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 283909d082cb..f1ddfc7b3b48 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -473,6 +473,10 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
 
 void __vm_area_free(struct vm_area_struct *vma)
 {
+#ifdef CONFIG_PER_VMA_LOCK
+	/* The vma should be detached while being destroyed. */
+	VM_BUG_ON_VMA(!is_vma_detached(vma), vma);
+#endif
 	vma_numab_state_free(vma);
 	free_anon_vma_name(vma);
 	kmem_cache_free(vm_area_cachep, vma);
diff --git a/mm/vma.c b/mm/vma.c
index fbd7254517d6..0436a7d21e01 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -413,9 +413,15 @@ void remove_vma(struct vm_area_struct *vma, bool unreachable)
 	if (vma->vm_file)
 		fput(vma->vm_file);
 	mpol_put(vma_policy(vma));
-	if (unreachable)
+	if (unreachable) {
+#ifdef CONFIG_PER_VMA_LOCK
+		if (!is_vma_detached(vma)) {
+			vma_start_write(vma);
+			vma_mark_detached(vma);
+		}
+#endif
 		__vm_area_free(vma);
-	else
+	} else
 		vm_area_free(vma);
 }
 
-- 
2.47.1.613.gc27f4b7a9f-goog