mm: add new mmget() helper

Apart from adding the helper function itself, the rest of the kernel is
converted mechanically using:

  git grep -l 'atomic_inc.*mm_users' | xargs sed -i 's/atomic_inc(&\(.*\)->mm_users);/mmget\(\1\);/'
  git grep -l 'atomic_inc.*mm_users' | xargs sed -i 's/atomic_inc(&\(.*\)\.mm_users);/mmget\(\&\1\);/'

This is needed for a later patch that hooks into the helper, but might
be a worthwhile cleanup on its own.

(Michal Hocko provided most of the kerneldoc comment.)

Link: http://lkml.kernel.org/r/20161218123229.22952-2-vegard.nossum@oracle.com
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 5 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 2cac12cc9abe..7a0713b76668 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1671,7 +1671,7 @@ int try_to_unuse(unsigned int type, bool frontswap,
          * that.
          */
         start_mm = &init_mm;
-        atomic_inc(&init_mm.mm_users);
+        mmget(&init_mm);
 
         /*
          * Keep on scanning until all entries have gone.  Usually,
@@ -1720,7 +1720,7 @@ int try_to_unuse(unsigned int type, bool frontswap,
                 if (atomic_read(&start_mm->mm_users) == 1) {
                         mmput(start_mm);
                         start_mm = &init_mm;
-                        atomic_inc(&init_mm.mm_users);
+                        mmget(&init_mm);
                 }
 
                 /*
@@ -1757,8 +1757,8 @@ int try_to_unuse(unsigned int type, bool frontswap,
                         struct mm_struct *prev_mm = start_mm;
                         struct mm_struct *mm;
 
-                        atomic_inc(&new_start_mm->mm_users);
-                        atomic_inc(&prev_mm->mm_users);
+                        mmget(new_start_mm);
+                        mmget(prev_mm);
                         spin_lock(&mmlist_lock);
                         while (swap_count(*swap_map) && !retval &&
                                         (p = p->next) != &start_mm->mmlist) {
@@ -1781,7 +1781,7 @@ int try_to_unuse(unsigned int type, bool frontswap,
 
                                 if (set_start_mm && *swap_map < swcount) {
                                         mmput(new_start_mm);
-                                        atomic_inc(&mm->mm_users);
+                                        mmget(mm);
                                         new_start_mm = mm;
                                         set_start_mm = 0;
                                 }