mm: move use_mm/unuse_mm from aio.c to mm/

Anyone who wants to do copy to/from user from a kernel thread, needs
use_mm (like what fs/aio has).  Move that into mm/, to make reusing and
exporting easier down the line, and make aio use it.  Next intended user,
besides aio, will be vhost-net.
Acked-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/aio.c

@@ -24,6 +24,7 @@
 #include <linux/file.h>
 #include <linux/mm.h>
 #include <linux/mman.h>
+#include <linux/mmu_context.h>
 #include <linux/slab.h>
 #include <linux/timer.h>
 #include <linux/aio.h>
@@ -34,7 +35,6 @@
 
 #include <asm/kmap_types.h>
 #include <asm/uaccess.h>
-#include <asm/mmu_context.h>
 
 #if DEBUG > 1
 #define dprintk		printk
@@ -594,51 +594,6 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
 	return ret;
 }
 
-/*
- * use_mm
- *	Makes the calling kernel thread take on the specified
- *	mm context.
- *	Called by the retry thread execute retries within the
- *	iocb issuer's mm context, so that copy_from/to_user
- *	operations work seamlessly for aio.
- *	(Note: this routine is intended to be called only
- *	from a kernel thread context)
- */
-static void use_mm(struct mm_struct *mm)
-{
-	struct mm_struct *active_mm;
-	struct task_struct *tsk = current;
-
-	task_lock(tsk);
-	active_mm = tsk->active_mm;
-	atomic_inc(&mm->mm_count);
-	tsk->mm = mm;
-	tsk->active_mm = mm;
-	switch_mm(active_mm, mm, tsk);
-	task_unlock(tsk);
-
-	mmdrop(active_mm);
-}
-
-/*
- * unuse_mm
- *	Reverses the effect of use_mm, i.e. releases the
- *	specified mm context which was earlier taken on
- *	by the calling kernel thread
- *	(Note: this routine is intended to be called only
- *	from a kernel thread context)
- */
-static void unuse_mm(struct mm_struct *mm)
-{
-	struct task_struct *tsk = current;
-
-	task_lock(tsk);
-	tsk->mm = NULL;
-	/* active_mm is still 'mm' */
-	enter_lazy_tlb(mm, tsk);
-	task_unlock(tsk);
-}
-
 /*
  * Queue up a kiocb to be retried. Assumes that the kiocb
  * has already been marked as kicked, and places it on

include/linux/mmu_context.h

+#ifndef _LINUX_MMU_CONTEXT_H
+#define _LINUX_MMU_CONTEXT_H
+
+struct mm_struct;
+
+void use_mm(struct mm_struct *mm);
+void unuse_mm(struct mm_struct *mm);
+
+#endif

mm/Makefile

@@ -11,7 +11,7 @@ obj-y			:= bootmem.o filemap.o mempool.o oom_kill.o fadvise.o \
 			   maccess.o page_alloc.o page-writeback.o \
 			   readahead.o swap.o truncate.o vmscan.o shmem.o \
 			   prio_tree.o util.o mmzone.o vmstat.o backing-dev.o \
-			   page_isolation.o mm_init.o $(mmu-y)
+			   page_isolation.o mm_init.o mmu_context.o $(mmu-y)
 obj-y += init-mm.o
 
 obj-$(CONFIG_PROC_PAGE_MONITOR) += pagewalk.o

mm/mmu_context.c

+/* Copyright (C) 2009 Red Hat, Inc.
+ *
+ * See ../COPYING for licensing terms.
+ */
+
+#include <linux/mm.h>
+#include <linux/mmu_context.h>
+#include <linux/sched.h>
+
+#include <asm/mmu_context.h>
+
+/*
+ * use_mm
+ *	Makes the calling kernel thread take on the specified
+ *	mm context.
+ *	Called by the retry thread execute retries within the
+ *	iocb issuer's mm context, so that copy_from/to_user
+ *	operations work seamlessly for aio.
+ *	(Note: this routine is intended to be called only
+ *	from a kernel thread context)
+ */
+void use_mm(struct mm_struct *mm)
+{
+	struct mm_struct *active_mm;
+	struct task_struct *tsk = current;
+
+	task_lock(tsk);
+	active_mm = tsk->active_mm;
+	atomic_inc(&mm->mm_count);
+	tsk->mm = mm;
+	tsk->active_mm = mm;
+	switch_mm(active_mm, mm, tsk);
+	task_unlock(tsk);
+
+	mmdrop(active_mm);
+}
+
+/*
+ * unuse_mm
+ *	Reverses the effect of use_mm, i.e. releases the
+ *	specified mm context which was earlier taken on
+ *	by the calling kernel thread
+ *	(Note: this routine is intended to be called only
+ *	from a kernel thread context)
+ */
+void unuse_mm(struct mm_struct *mm)
+{
+	struct task_struct *tsk = current;
+
+	task_lock(tsk);
+	tsk->mm = NULL;
+	/* active_mm is still 'mm' */
+	enter_lazy_tlb(mm, tsk);
+	task_unlock(tsk);
+}