[PATCH v2 25/35] mm: add mmu_notifier_trylock() and mmu_notifier_unlock()

[Michel Lespinasse]

These new functions are to be used when firing MMU notifications
without holding any of the mmap or rmap locks, as is the case with
speculative page fault handlers.

Signed-off-by: Michel Lespinasse <michel@xxxxxxxxxxxxxx>
---
 include/linux/mmu_notifier.h | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index ace76fe91c0c..d0430410fdd8 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -772,4 +772,29 @@ static inline void mmu_notifier_synchronize(void)
 
 #endif /* CONFIG_MMU_NOTIFIER */
 
+#if defined(CONFIG_MMU_NOTIFIER) && defined(CONFIG_SPECULATIVE_PAGE_FAULT)
+
+static inline bool mmu_notifier_trylock(struct mm_struct *mm)
+{
+	return percpu_down_read_trylock(mm->mmu_notifier_lock);
+}
+
+static inline void mmu_notifier_unlock(struct mm_struct *mm)
+{
+	percpu_up_read(mm->mmu_notifier_lock);
+}
+
+#else
+
+static inline bool mmu_notifier_trylock(struct mm_struct *mm)
+{
+	return true;
+}
+
+static inline void mmu_notifier_unlock(struct mm_struct *mm)
+{
+}
+
+#endif
+
 #endif /* _LINUX_MMU_NOTIFIER_H */
-- 
2.20.1