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>

4 files changed, 66 insertions, 47 deletions

diff --git a/fs/aio.c b/fs/aio.c
index d065b2c3273e..fc21c23b2387 100644
--- a/fs/aio.c
+++ b/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
@@ -595,51 +595,6 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
 }
 
 /*
- * 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
  * the retry run list for the corresponding ioctx, if it
diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h
new file mode 100644
index 000000000000..70fffeba7495
--- /dev/null
+++ b/include/linux/mmu_context.h
@@ -0,0 +1,9 @@
+#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
diff --git a/mm/Makefile b/mm/Makefile
index a63bf59a0c77..728a9fde49d1 100644
--- a/mm/Makefile
+++ b/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
diff --git a/mm/mmu_context.c b/mm/mmu_context.c
new file mode 100644
index 000000000000..fd473b51c903
--- /dev/null
+++ b/mm/mmu_context.c
@@ -0,0 +1,55 @@
+/* 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);
+}