path: root/mm/mmu_notifier.c
diff options
authorPeter Zijlstra <>2014-08-06 16:08:20 -0700
committerLinus Torvalds <>2014-08-06 18:01:22 -0700
commitb972216e27d1c853eced33f8638926636c606341 (patch)
tree163addfd60315832e514fd7b2aa23cadd6fb6bf9 /mm/mmu_notifier.c
parent1d352bfd41e8219cdf9bebe79677700bdc38b540 (diff)
mmu_notifier: add call_srcu and sync function for listener to delay call and sync
When kernel device drivers or subsystems want to bind their lifespan to t= he lifespan of the mm_struct, they usually use one of the following methods: 1. Manually calling a function in the interested kernel module. The funct= ion call needs to be placed in mmput. This method was rejected by several ker= nel maintainers. 2. Registering to the mmu notifier release mechanism. The problem with the latter approach is that the mmu_notifier_release cal= lback is called from__mmu_notifier_release (called from exit_mmap). That functi= on iterates over the list of mmu notifiers and don't expect the release call= back function to remove itself from the list. Therefore, the callback function= in the kernel module can't release the mmu_notifier_object, which is actuall= y the kernel module's object itself. As a result, the destruction of the kernel module's object must to be done in a delayed fashion. This patch adds support for this delayed callback, by adding a new mmu_notifier_call_srcu function that receives a function ptr and calls th= at function with call_srcu. In that function, the kernel module releases its object. To use mmu_notifier_call_srcu, the calling module needs to call b= efore that a new function called mmu_notifier_unregister_no_release that as its= name implies, unregisters a notifier without calling its notifier release call= back. This patch also adds a function that will call barrier_srcu so those kern= el modules can sync with mmu_notifier. Signed-off-by: Peter Zijlstra <> Signed-off-by: Jérôme Glisse <> Signed-off-by: Oded Gabbay <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'mm/mmu_notifier.c')
1 files changed, 39 insertions, 1 deletions
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 41cefdf0aadd..950813b1eb36 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -23,6 +23,25 @@
static struct srcu_struct srcu;
+ * This function allows mmu_notifier::release callback to delay a call to
+ * a function that will free appropriate resources. The function must be
+ * quick and must not block.
+ */
+void mmu_notifier_call_srcu(struct rcu_head *rcu,
+ void (*func)(struct rcu_head *rcu))
+ call_srcu(&srcu, rcu, func);
+void mmu_notifier_synchronize(void)
+ /* Wait for any running method to finish. */
+ srcu_barrier(&srcu);
* This function can't run concurrently against mmu_notifier_register
* because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
* runs with mm_users == 0. Other tasks may still invoke mmu notifiers
@@ -53,7 +72,6 @@ void __mmu_notifier_release(struct mm_struct *mm)
if (mn->ops->release)
mn->ops->release(mn, mm);
- srcu_read_unlock(&srcu, id);
while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
@@ -69,6 +87,7 @@ void __mmu_notifier_release(struct mm_struct *mm)
+ srcu_read_unlock(&srcu, id);
* synchronize_srcu here prevents mmu_notifier_release from returning to
@@ -325,6 +344,25 @@ void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
+ * Same as mmu_notifier_unregister but no callback and no srcu synchronization.
+ */
+void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
+ struct mm_struct *mm)
+ spin_lock(&mm->mmu_notifier_mm->lock);
+ /*
+ * Can not use list_del_rcu() since __mmu_notifier_release
+ * can delete it before we hold the lock.
+ */
+ hlist_del_init_rcu(&mn->hlist);
+ spin_unlock(&mm->mmu_notifier_mm->lock);
+ BUG_ON(atomic_read(&mm->mm_count) <= 0);
+ mmdrop(mm);
static int __init mmu_notifier_init(void)
return init_srcu_struct(&srcu);