From: Sagi Grimberg <sagig@xxxxxxxxxxxxxx>
Now that anon_vma lock and i_mmap_mutex are both sleepable mutex, it is possible to schedule inside invalidation callbacks
(such as invalidate_page, invalidate_range_start/end and change_pte) .
This is essential for a scheduling HW sync in RDMA drivers which apply on demand paging methods.
Signed-off-by: Sagi Grimberg <sagig@xxxxxxxxxxxxxx>
---
changes from V1:
1. converted synchronize_rcu() to synchronize_srcu() to racing candidates (unregister, release)
2. do_mmu_notifier_register: moved init_srcu_struct out of mmap_sem locking.
3. do_mmu_notifier_register: fixed error path.
include/linux/mmu_notifier.h | 3 +++
mm/mmu_notifier.c | 38 +++++++++++++++++++++++++-------------
2 files changed, 28 insertions(+), 13 deletions(-)
diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index 1d1b1e1..f3d6f30 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -4,6 +4,7 @@
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/mm_types.h>
+#include <linux/srcu.h>
struct mmu_notifier;
struct mmu_notifier_ops;
@@ -21,6 +22,8 @@ struct mmu_notifier_mm {
struct hlist_head list;
/* to serialize the list modifications and hlist_unhashed */
spinlock_t lock;
+ /* to enable sleeping in callbacks */
+ struct srcu_struct srcu;
};
struct mmu_notifier_ops {
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 9a611d3..7267fb2 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -67,7 +67,7 @@ void __mmu_notifier_release(struct mm_struct *mm)
spin_unlock(&mm->mmu_notifier_mm->lock);
/*
- * synchronize_rcu here prevents mmu_notifier_release to
+ * synchronize_srcu here prevents mmu_notifier_release to
* return to exit_mmap (which would proceed freeing all pages
* in the mm) until the ->release method returns, if it was
* invoked by mmu_notifier_unregister.
@@ -75,7 +75,7 @@ void __mmu_notifier_release(struct mm_struct *mm)
* The mmu_notifier_mm can't go away from under us because one
* mm_count is hold by exit_mmap.
*/
- synchronize_rcu();
+ synchronize_srcu(&mm->mmu_notifier_mm->srcu);
}
/*
@@ -123,10 +123,11 @@ int __mmu_notifier_test_young(struct mm_struct *mm,
void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
pte_t pte)
{
+ int idx;
struct mmu_notifier *mn;
struct hlist_node *n;
- rcu_read_lock();
+ idx = srcu_read_lock(&mm->mmu_notifier_mm->srcu);
hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
if (mn->ops->change_pte)
mn->ops->change_pte(mn, mm, address, pte);
@@ -137,49 +138,52 @@ void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
else if (mn->ops->invalidate_page)
mn->ops->invalidate_page(mn, mm, address);
}
- rcu_read_unlock();
+ srcu_read_unlock(&mm->mmu_notifier_mm->srcu, idx);
}
void __mmu_notifier_invalidate_page(struct mm_struct *mm,
unsigned long address)
{
+ int idx;
struct mmu_notifier *mn;
struct hlist_node *n;
- rcu_read_lock();
+ idx = srcu_read_lock(&mm->mmu_notifier_mm->srcu);
hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
if (mn->ops->invalidate_page)
mn->ops->invalidate_page(mn, mm, address);
}
- rcu_read_unlock();
+ srcu_read_unlock(&mm->mmu_notifier_mm->srcu, idx);
}
void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
unsigned long start, unsigned long end)
{
+ int idx;
struct mmu_notifier *mn;
struct hlist_node *n;
- rcu_read_lock();
+ idx = srcu_read_lock(&mm->mmu_notifier_mm->srcu);
hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
if (mn->ops->invalidate_range_start)
mn->ops->invalidate_range_start(mn, mm, start, end);
}
- rcu_read_unlock();
+ srcu_read_unlock(&mm->mmu_notifier_mm->srcu, idx);
}
void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
unsigned long start, unsigned long end)
{
+ int idx;
struct mmu_notifier *mn;
struct hlist_node *n;
- rcu_read_lock();
+ idx = srcu_read_lock(&mm->mmu_notifier_mm->srcu);
hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
if (mn->ops->invalidate_range_end)
mn->ops->invalidate_range_end(mn, mm, start, end);
}
- rcu_read_unlock();
+ srcu_read_unlock(&mm->mmu_notifier_mm->srcu, idx);
}
static int do_mmu_notifier_register(struct mmu_notifier *mn,
@@ -196,6 +200,9 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn,
if (unlikely(!mmu_notifier_mm))
goto out;
+ if (init_srcu_struct(&mmu_notifier_mm->srcu))
+ goto out_cleanup;
+
if (take_mmap_sem)
down_write(&mm->mmap_sem);
ret = mm_take_all_locks(mm);
@@ -226,8 +233,12 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn,
out_cleanup:
if (take_mmap_sem)
up_write(&mm->mmap_sem);
- /* kfree() does nothing if mmu_notifier_mm is NULL */
- kfree(mmu_notifier_mm);
+
+ if (mm->mmu_notifier_mm) {
+ /* in the case srcu_init failed srcu_cleanup is safe */
+ cleanup_srcu_struct(&mm->mmu_notifier_mm->srcu);
+ kfree(mmu_notifier_mm);
+ }
out:
BUG_ON(atomic_read(&mm->mm_users) <= 0);
return ret;
@@ -266,6 +277,7 @@ EXPORT_SYMBOL_GPL(__mmu_notifier_register);
void __mmu_notifier_mm_destroy(struct mm_struct *mm)
{
BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
+ cleanup_srcu_struct(&mm->mmu_notifier_mm->srcu);
kfree(mm->mmu_notifier_mm);
mm->mmu_notifier_mm = LIST_POISON1; /* debug */
}
@@ -309,7 +321,7 @@ void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
* Wait any running method to finish, of course including
* ->release if it was run by mmu_notifier_relase instead of us.
*/
- synchronize_rcu();
+ synchronize_srcu(&mm->mmu_notifier_mm->srcu);
BUG_ON(atomic_read(&mm->mm_count) <= 0);
--
1.7.8.2
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