mm: factor out main logic of access_process_vm

Introduce an internal helper __access_remote_vm and base access_process_vm on
top of it.  This new method may be called with a NULL task_struct if page fault
accounting is not desired.  This code will be shared with a new address space
accessor that is independent of task_struct.

Signed-off-by: Stephen Wilson <wilsons@start.ca>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 25 insertions, 10 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 5f585b65d734..820b4c4810f0 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3650,20 +3650,15 @@ int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
 #endif
 
 /*
- * Access another process' address space.
- * Source/target buffer must be kernel space,
- * Do not walk the page table directly, use get_user_pages
+ * Access another process' address space as given in mm.  If non-NULL, use the
+ * given task for page fault accounting.
  */
-int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write)
+static int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
+                unsigned long addr, void *buf, int len, int write)
 {
-        struct mm_struct *mm;
         struct vm_area_struct *vma;
         void *old_buf = buf;
 
-        mm = get_task_mm(tsk);
-        if (!mm)
-                return 0;
-
         down_read(&mm->mmap_sem);
         /* ignore errors, just check how much was successfully transferred */
         while (len) {
@@ -3712,12 +3707,32 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in
                 addr += bytes;
         }
         up_read(&mm->mmap_sem);
-        mmput(mm);
 
         return buf - old_buf;
 }
 
 /*
+ * Access another process' address space.
+ * Source/target buffer must be kernel space,
+ * Do not walk the page table directly, use get_user_pages
+ */
+int access_process_vm(struct task_struct *tsk, unsigned long addr,
+                void *buf, int len, int write)
+{
+        struct mm_struct *mm;
+        int ret;
+
+        mm = get_task_mm(tsk);
+        if (!mm)
+                return 0;
+
+        ret = __access_remote_vm(tsk, mm, addr, buf, len, write);
+        mmput(mm);
+
+        return ret;
+}
+
+/*
  * Print the name of a VMA.
  */
 void print_vma_addr(char *prefix, unsigned long ip)