Re: [PATCH v2] android: binder: Drop lru lock in isolate callback

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 14 Sep 2017 14:22:25 -0400 Sherry Yang <sherryy@android.com> wrote:

> Drop the global lru lock in isolate callback
> before calling zap_page_range which calls
> cond_resched, and re-acquire the global lru
> lock before returning. Also change return
> code to LRU_REMOVED_RETRY.
> 
> Use mmput_async when fail to acquire mmap sem
> in an atomic context.
> 
> Fix "BUG: sleeping function called from invalid context"
> errors when CONFIG_DEBUG_ATOMIC_SLEEP is enabled.
> 
> Also restore mmput_async, which was initially introduced in
> ec8d7c14e ("mm, oom_reaper: do not mmput synchronously from
> the oom reaper context"), and was removed in 212925802
> ("mm: oom: let oom_reap_task and exit_mmap run concurrently").

Ho hum, OK.  It's a bit sad to bring this back for one caller but
mm.async_put_work is there and won't be going away.

The mmdrop_async stuff should be moved into fork.c (and maybe made
static) as well.  It's pointless having this stuff global and inlined,
especially mmdrop_async_fn().


Something like the below, not yet tested...


From: Andrew Morton <akpm@linux-foundation.org>
Subject: include/linux/sched/mm.h: uninline mmdrop_async(), etc

mmdrop_async() is only used in fork.c.  Move that and its support functions
into fork.c, uninline it all.



Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/sched/mm.h |   24 +--------------
 kernel/fork.c            |   58 +++++++++++++++++++++++++------------
 2 files changed, 42 insertions(+), 40 deletions(-)

diff -puN include/linux/sched/mm.h~a include/linux/sched/mm.h
--- a/include/linux/sched/mm.h~a
+++ a/include/linux/sched/mm.h
@@ -10,7 +10,7 @@
 /*
  * Routines for handling mm_structs
  */
-extern struct mm_struct * mm_alloc(void);
+extern struct mm_struct *mm_alloc(void);
 
 /**
  * mmgrab() - Pin a &struct mm_struct.
@@ -34,27 +34,7 @@ static inline void mmgrab(struct mm_stru
 	atomic_inc(&mm->mm_count);
 }
 
-/* mmdrop drops the mm and the page tables */
-extern void __mmdrop(struct mm_struct *);
-static inline void mmdrop(struct mm_struct *mm)
-{
-	if (unlikely(atomic_dec_and_test(&mm->mm_count)))
-		__mmdrop(mm);
-}
-
-static inline void mmdrop_async_fn(struct work_struct *work)
-{
-	struct mm_struct *mm = container_of(work, struct mm_struct, async_put_work);
-	__mmdrop(mm);
-}
-
-static inline void mmdrop_async(struct mm_struct *mm)
-{
-	if (unlikely(atomic_dec_and_test(&mm->mm_count))) {
-		INIT_WORK(&mm->async_put_work, mmdrop_async_fn);
-		schedule_work(&mm->async_put_work);
-	}
-}
+extern void mmdrop(struct mm_struct *mm);
 
 /**
  * mmget() - Pin the address space associated with a &struct mm_struct.
diff -puN kernel/fork.c~a kernel/fork.c
--- a/kernel/fork.c~a
+++ a/kernel/fork.c
@@ -386,6 +386,46 @@ void free_task(struct task_struct *tsk)
 }
 EXPORT_SYMBOL(free_task);
 
+/*
+ * Called when the last reference to the mm
+ * is dropped: either by a lazy thread or by
+ * mmput. Free the page directory and the mm.
+ */
+static void __mmdrop(struct mm_struct *mm)
+{
+	BUG_ON(mm == &init_mm);
+	mm_free_pgd(mm);
+	destroy_context(mm);
+	hmm_mm_destroy(mm);
+	mmu_notifier_mm_destroy(mm);
+	check_mm(mm);
+	put_user_ns(mm->user_ns);
+	free_mm(mm);
+}
+
+void mmdrop(struct mm_struct *mm)
+{
+	if (unlikely(atomic_dec_and_test(&mm->mm_count)))
+		__mmdrop(mm);
+}
+EXPORT_SYMBOL_GPL(mmdrop)
+
+static void mmdrop_async_fn(struct work_struct *work)
+{
+	struct mm_struct *mm;
+
+	mm = container_of(work, struct mm_struct, async_put_work);
+	__mmdrop(mm);
+}
+
+static void mmdrop_async(struct mm_struct *mm)
+{
+	if (unlikely(atomic_dec_and_test(&mm->mm_count))) {
+		INIT_WORK(&mm->async_put_work, mmdrop_async_fn);
+		schedule_work(&mm->async_put_work);
+	}
+}
+
 static inline void free_signal_struct(struct signal_struct *sig)
 {
 	taskstats_tgid_free(sig);
@@ -895,24 +935,6 @@ struct mm_struct *mm_alloc(void)
 	return mm_init(mm, current, current_user_ns());
 }
 
-/*
- * Called when the last reference to the mm
- * is dropped: either by a lazy thread or by
- * mmput. Free the page directory and the mm.
- */
-void __mmdrop(struct mm_struct *mm)
-{
-	BUG_ON(mm == &init_mm);
-	mm_free_pgd(mm);
-	destroy_context(mm);
-	hmm_mm_destroy(mm);
-	mmu_notifier_mm_destroy(mm);
-	check_mm(mm);
-	put_user_ns(mm->user_ns);
-	free_mm(mm);
-}
-EXPORT_SYMBOL_GPL(__mmdrop);
-
 static inline void __mmput(struct mm_struct *mm)
 {
 	VM_BUG_ON(atomic_read(&mm->mm_users));
_