From: Suren Baghdasaryan <surenb@google.com>
Date: Thu, 7 Jul 2022 23:24:22 +0000 (-0700)
Subject: kernel/fork: assert no VMA readers during its destruction
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=1d57e5bd55696ec9024775d9cbd10e6715a37fe2;p=users%2Fjedix%2Flinux-maple.git

kernel/fork: assert no VMA readers during its destruction

Assert there are no holders of VMA lock for reading when it is about to be
destroyed.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ecb1cd991443..3851f786c95a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -677,6 +677,13 @@ static inline void vma_assert_write_locked(struct vm_area_struct *vma)
 	VM_BUG_ON_VMA(vma->vm_lock_seq != READ_ONCE(vma->vm_mm->mm_lock_seq), vma);
 }
 
+static inline void vma_assert_no_reader(struct vm_area_struct *vma)
+{
+	VM_BUG_ON_VMA(rwsem_is_locked(&vma->lock) &&
+		      vma->vm_lock_seq != READ_ONCE(vma->vm_mm->mm_lock_seq),
+		      vma);
+}
+
 #else /* CONFIG_PER_VMA_LOCK */
 
 static inline void vma_init_lock(struct vm_area_struct *vma) {}
@@ -686,6 +693,7 @@ static inline bool vma_read_trylock(struct vm_area_struct *vma)
 static inline void vma_read_unlock(struct vm_area_struct *vma) {}
 static inline void vma_assert_locked(struct vm_area_struct *vma) {}
 static inline void vma_assert_write_locked(struct vm_area_struct *vma) {}
+static inline void vma_assert_no_reader(struct vm_area_struct *vma) {}
 
 #endif /* CONFIG_PER_VMA_LOCK */
 
diff --git a/kernel/fork.c b/kernel/fork.c
index a3e06c2e5432..b3a7ffc2c0a4 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -485,6 +485,8 @@ static void __vm_area_free(struct rcu_head *head)
 {
 	struct vm_area_struct *vma = container_of(head, struct vm_area_struct,
 						  vm_rcu);
+	/* The vma should either have no lock holders or be write-locked. */
+	vma_assert_no_reader(vma);
 	kmem_cache_free(vm_area_cachep, vma);
 }
 #endif