[PATCH] mmotm: mm-oom_reaper-do-not-mmput-synchronously-from-the-oom-reaper-context-fix

[Michal Hocko]

mmput_async is currently used only from the oom_reaper which is defined
only for CONFIG_MMU. We can save work_struct in mm_struct for
!CONFIG_MMU.

Reported-by: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
 include/linux/mm_types.h | 2 ++
 include/linux/sched.h    | 2 ++
 kernel/fork.c            | 2 ++
 3 files changed, 6 insertions(+)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index ab142ace96f3..a16dcb2efca4 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -514,7 +514,9 @@ struct mm_struct {
 #ifdef CONFIG_HUGETLB_PAGE
 	atomic_long_t hugetlb_usage;
 #endif
+#ifdef CONFIG_MMU
 	struct work_struct async_put_work;
+#endif
 };
 
 static inline void mm_init_cpumask(struct mm_struct *mm)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index df8778e72211..11b31ded65cf 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2604,10 +2604,12 @@ static inline void mmdrop(struct mm_struct * mm)
 
 /* mmput gets rid of the mappings and all user-space */
 extern void mmput(struct mm_struct *);
+#ifdef CONFIG_MMU
 /* same as above but performs the slow path from the async kontext. Can
  * be called from the atomic context as well
  */
 extern void mmput_async(struct mm_struct *);
+#endif
 
 /* Grab a reference to a task's mm, if it is not already going away */
 extern struct mm_struct *get_task_mm(struct task_struct *task);
diff --git a/kernel/fork.c b/kernel/fork.c
index e1dc6b02ac8b..1e3dc3af6845 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -732,6 +732,7 @@ void mmput(struct mm_struct *mm)
 }
 EXPORT_SYMBOL_GPL(mmput);
 
+#ifdef CONFIG_MMU
 static void mmput_async_fn(struct work_struct *work)
 {
 	struct mm_struct *mm = container_of(work, struct mm_struct, async_put_work);
@@ -745,6 +746,7 @@ void mmput_async(struct mm_struct *mm)
 		schedule_work(&mm->async_put_work);
 	}
 }
+#endif
 
 /**
  * set_mm_exe_file - change a reference to the mm's executable file
-- 
2.8.1


-- 
Michal Hocko
SUSE Labs