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SubjectRe: [PATCH v2] android: binder: Drop lru lock in isolate callback
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));
_
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