The patch titled
Subject: mm: mmu_notifier: fix freed page still mapped in secondary MMU
has been added to the -mm tree. Its filename is
mm-mmu_notifier-fix-freed-page-still-mapped-in-secondary-mmu.patch
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------------------------------------------------------
From: Xiao Guangrong <[email protected]>
Subject: mm: mmu_notifier: fix freed page still mapped in secondary MMU
mmu_notifier_release() is called when the process is exiting. It will
delete all the mmu notifiers. But at this time the page belonging to the
process is still present in page tables and is present on the LRU list, so
this race will happen:
CPU 0 CPU 1
mmu_notifier_release: try_to_unmap:
hlist_del_init_rcu(&mn->hlist);
ptep_clear_flush_notify:
mmu nofifler not found
free page !!!!!!
/*
* At the point, the page has been
* freed, but it is still mapped in
* the secondary MMU.
*/
mn->ops->release(mn, mm);
Then the box is not stable and sometimes we can get this bug:
[ 738.075923] BUG: Bad page state in process migrate-perf pfn:03bec
[ 738.075931] page:ffffea00000efb00 count:0 mapcount:0 mapping:
(null) index:0x8076
[ 738.075936] page flags: 0x20000000000014(referenced|dirty)
The same issue is present in mmu_notifier_unregister().
We can call ->release before deleting the notifier to ensure the page has
been unmapped from the secondary MMU before it is freed.
Signed-off-by: Xiao Guangrong <[email protected]>
Cc: Avi Kivity <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
mm/mmu_notifier.c | 45 ++++++++++++++++++++++----------------------
1 file changed, 23 insertions(+), 22 deletions(-)
diff -puN
mm/mmu_notifier.c~mm-mmu_notifier-fix-freed-page-still-mapped-in-secondary-mmu
mm/mmu_notifier.c
---
a/mm/mmu_notifier.c~mm-mmu_notifier-fix-freed-page-still-mapped-in-secondary-mmu
+++ a/mm/mmu_notifier.c
@@ -33,6 +33,24 @@
void __mmu_notifier_release(struct mm_struct *mm)
{
struct mmu_notifier *mn;
+ struct hlist_node *n;
+
+ /*
+ * RCU here will block mmu_notifier_unregister until
+ * ->release returns.
+ */
+ rcu_read_lock();
+ hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist)
+ /*
+ * if ->release runs before mmu_notifier_unregister it
+ * must be handled as it's the only way for the driver
+ * to flush all existing sptes and stop the driver
+ * from establishing any more sptes before all the
+ * pages in the mm are freed.
+ */
+ if (mn->ops->release)
+ mn->ops->release(mn, mm);
+ rcu_read_unlock();
spin_lock(&mm->mmu_notifier_mm->lock);
while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
@@ -46,23 +64,6 @@ void __mmu_notifier_release(struct mm_st
* mmu_notifier_unregister to return.
*/
hlist_del_init_rcu(&mn->hlist);
- /*
- * RCU here will block mmu_notifier_unregister until
- * ->release returns.
- */
- rcu_read_lock();
- spin_unlock(&mm->mmu_notifier_mm->lock);
- /*
- * if ->release runs before mmu_notifier_unregister it
- * must be handled as it's the only way for the driver
- * to flush all existing sptes and stop the driver
- * from establishing any more sptes before all the
- * pages in the mm are freed.
- */
- if (mn->ops->release)
- mn->ops->release(mn, mm);
- rcu_read_unlock();
- spin_lock(&mm->mmu_notifier_mm->lock);
}
spin_unlock(&mm->mmu_notifier_mm->lock);
@@ -284,16 +285,13 @@ void mmu_notifier_unregister(struct mmu_
{
BUG_ON(atomic_read(&mm->mm_count) <= 0);
- spin_lock(&mm->mmu_notifier_mm->lock);
if (!hlist_unhashed(&mn->hlist)) {
- hlist_del_rcu(&mn->hlist);
-
/*
* RCU here will force exit_mmap to wait ->release to finish
* before freeing the pages.
*/
rcu_read_lock();
- spin_unlock(&mm->mmu_notifier_mm->lock);
+
/*
* exit_mmap will block in mmu_notifier_release to
* guarantee ->release is called before freeing the
@@ -302,8 +300,11 @@ void mmu_notifier_unregister(struct mmu_
if (mn->ops->release)
mn->ops->release(mn, mm);
rcu_read_unlock();
- } else
+
+ spin_lock(&mm->mmu_notifier_mm->lock);
+ hlist_del_rcu(&mn->hlist);
spin_unlock(&mm->mmu_notifier_mm->lock);
+ }
/*
* Wait any running method to finish, of course including
_
Subject: Subject: mm: mmu_notifier: fix freed page still mapped in secondary MMU
Patches currently in -mm which might be from [email protected]
are
linux-next.patch
mm-mmu_notifier-fix-freed-page-still-mapped-in-secondary-mmu.patch
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