+ mmu_notifier-add-call_srcu-and-sync-function-for-listener-to-delay-call-and-sync.patch added to -mm tree

+ mmu_notifier-add-call_srcu-and-sync-function-for-listener-to-delay-call-and-sync.patch added to -mm tree

[akpm]

The patch titled
     Subject: mmu_notifier: add call_srcu and sync function for listener to delay call and sync
has been added to the -mm tree.  Its filename is
     mmu_notifier-add-call_srcu-and-sync-function-for-listener-to-delay-call-and-sync.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mmu_notifier-add-call_srcu-and-sync-function-for-listener-to-delay-call-and-sync.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mmu_notifier-add-call_srcu-and-sync-function-for-listener-to-delay-call-and-sync.patch

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*** Remember to use Documentation/SubmitChecklist when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Peter Zijlstra <peterz@infradead.org>
Subject: mmu_notifier: add call_srcu and sync function for listener to delay call and sync


When kernel device drivers or subsystems want to bind their lifespan to t=
he lifespan of the mm_struct, they usually use one of the following
methods:

1.  Manually calling a function in the interested kernel module.  The
   funct= ion call needs to be placed in mmput.  This method was rejected
   by several ker= nel maintainers.

2. Registering to the mmu notifier release mechanism.

The problem with the latter approach is that the mmu_notifier_release cal=
lback is called from__mmu_notifier_release (called from exit_mmap).  That
functi= on iterates over the list of mmu notifiers and don't expect the
release call= back function to remove itself from the list.  Therefore,
the callback function= in the kernel module can't release the
mmu_notifier_object, which is actuall= y the kernel module's object
itself.  As a result, the destruction of the kernel module's object must
to be done in a delayed fashion.

This patch adds support for this delayed callback, by adding a new
mmu_notifier_call_srcu function that receives a function ptr and calls th=
at function with call_srcu.  In that function, the kernel module releases
its object.  To use mmu_notifier_call_srcu, the calling module needs to
call b= efore that a new function called
mmu_notifier_unregister_no_release that as its= name implies, unregisters
a notifier without calling its notifier release call= back.

This patch also adds a function that will call barrier_srcu so those kern=
el modules can sync with mmu_notifier.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mmu_notifier.h |    6 ++++
 mm/mmu_notifier.c            |   40 ++++++++++++++++++++++++++++++++-
 2 files changed, 45 insertions(+), 1 deletion(-)

diff -puN include/linux/mmu_notifier.h~mmu_notifier-add-call_srcu-and-sync-function-for-listener-to-delay-call-and-sync include/linux/mmu_notifier.h
--- a/include/linux/mmu_notifier.h~mmu_notifier-add-call_srcu-and-sync-function-for-listener-to-delay-call-and-sync
+++ a/include/linux/mmu_notifier.h
@@ -170,6 +170,8 @@ extern int __mmu_notifier_register(struc
 				   struct mm_struct *mm);
 extern void mmu_notifier_unregister(struct mmu_notifier *mn,
 				    struct mm_struct *mm);
+extern void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
+					       struct mm_struct *mm);
 extern void __mmu_notifier_mm_destroy(struct mm_struct *mm);
 extern void __mmu_notifier_release(struct mm_struct *mm);
 extern int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
@@ -288,6 +290,10 @@ static inline void mmu_notifier_mm_destr
 	set_pte_at(___mm, ___address, __ptep, ___pte);			\
 })
 
+extern void mmu_notifier_call_srcu(struct rcu_head *rcu,
+				   void (*func)(struct rcu_head *rcu));
+extern void mmu_notifier_synchronize(void);
+
 #else /* CONFIG_MMU_NOTIFIER */
 
 static inline void mmu_notifier_release(struct mm_struct *mm)
diff -puN mm/mmu_notifier.c~mmu_notifier-add-call_srcu-and-sync-function-for-listener-to-delay-call-and-sync mm/mmu_notifier.c
--- a/mm/mmu_notifier.c~mmu_notifier-add-call_srcu-and-sync-function-for-listener-to-delay-call-and-sync
+++ a/mm/mmu_notifier.c
@@ -23,6 +23,25 @@
 static struct srcu_struct srcu;
 
 /*
+ * This function allows mmu_notifier::release callback to delay a call to
+ * a function that will free appropriate resources. The function must be
+ * quick and must not block.
+ */
+void mmu_notifier_call_srcu(struct rcu_head *rcu,
+			    void (*func)(struct rcu_head *rcu))
+{
+	call_srcu(&srcu, rcu, func);
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_call_srcu);
+
+void mmu_notifier_synchronize(void)
+{
+	/* Wait for any running method to finish. */
+	srcu_barrier(&srcu);
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_synchronize);
+
+/*
  * This function can't run concurrently against mmu_notifier_register
  * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
  * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
@@ -53,7 +72,6 @@ void __mmu_notifier_release(struct mm_st
 		 */
 		if (mn->ops->release)
 			mn->ops->release(mn, mm);
-	srcu_read_unlock(&srcu, id);
 
 	spin_lock(&mm->mmu_notifier_mm->lock);
 	while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
@@ -69,6 +87,7 @@ void __mmu_notifier_release(struct mm_st
 		hlist_del_init_rcu(&mn->hlist);
 	}
 	spin_unlock(&mm->mmu_notifier_mm->lock);
+	srcu_read_unlock(&srcu, id);
 
 	/*
 	 * synchronize_srcu here prevents mmu_notifier_release from returning to
@@ -325,6 +344,25 @@ void mmu_notifier_unregister(struct mmu_
 }
 EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
 
+/*
+ * Same as mmu_notifier_unregister but no callback and no srcu synchronization.
+ */
+void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
+					struct mm_struct *mm)
+{
+	spin_lock(&mm->mmu_notifier_mm->lock);
+	/*
+	 * Can not use list_del_rcu() since __mmu_notifier_release
+	 * can delete it before we hold the lock.
+	 */
+	hlist_del_init_rcu(&mn->hlist);
+	spin_unlock(&mm->mmu_notifier_mm->lock);
+
+	BUG_ON(atomic_read(&mm->mm_count) <= 0);
+	mmdrop(mm);
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);
+
 static int __init mmu_notifier_init(void)
 {
 	return init_srcu_struct(&srcu);
_

Patches currently in -mm which might be from peterz@infradead.org are

vmstat-on-demand-vmstat-workers-v8.patch
vmstat-on-demand-vmstat-workers-v8-do-not-open-code-alloc_cpumask_var.patch
mmu_notifier-add-call_srcu-and-sync-function-for-listener-to-delay-call-and-sync.patch
makefile-tell-gcc-optimizer-to-never-introduce-new-data-races.patch
linux-next.patch
x86-vdso-fix-vdso2cs-special_pages-error-checking.patch
timer-provide-an-api-for-deferrable-timeout.patch
ksm-provide-support-to-use-deferrable-timers-for-scanner-thread.patch
ksm-provide-support-to-use-deferrable-timers-for-scanner-thread-fix.patch
ksm-provide-support-to-use-deferrable-timers-for-scanner-thread-fix-fix-2.patch
mm-replace-remap_file_pages-syscall-with-emulation.patch
mm-replace-remap_file_pages-syscall-with-emulation-fix.patch

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