linux-kernel - [RFC PATCH 16/28] kernel/fork: assert no VMA readers during its destruction

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Date:   Mon, 29 Aug 2022 21:25:19 +0000
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     akpm@...ux-foundation.org
Cc:     michel@...pinasse.org, jglisse@...gle.com, mhocko@...e.com,
        vbabka@...e.cz, hannes@...xchg.org, mgorman@...hsingularity.net,
        dave@...olabs.net, willy@...radead.org, liam.howlett@...cle.com,
        peterz@...radead.org, ldufour@...ux.ibm.com,
        laurent.dufour@...ibm.com, paulmck@...nel.org, riel@...riel.com,
        luto@...nel.org, songliubraving@...com, peterx@...hat.com,
        david@...hat.com, dhowells@...hat.com, hughd@...gle.com,
        bigeasy@...utronix.de, kent.overstreet@...ux.dev,
        rientjes@...gle.com, axelrasmussen@...gle.com, joelaf@...gle.com,
        minchan@...gle.com, surenb@...gle.com, kernel-team@...roid.com,
        linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [RFC PATCH 16/28] 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@...gle.com>
---
 include/linux/mm.h | 8 ++++++++
 kernel/fork.c      | 2 ++
 2 files changed, 10 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index dc72be923e5b..0d9c1563c354 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -676,6 +676,13 @@ static inline void vma_assert_write_locked(struct vm_area_struct *vma, int pos)
 	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) {}
@@ -685,6 +692,7 @@ 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, int pos) {}
+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 1872ad549fed..b443ba3a247a 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -487,6 +487,8 @@ 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
-- 
2.37.2.672.g94769d06f0-goog