mm: add new mmgrab() helper

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

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

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/20161218123229.22952-1-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, 2 insertions, 2 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index b8f06273353e..5d51a188871b 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -766,7 +766,7 @@ struct mm_struct *proc_mem_open(struct inode *inode, unsigned int mode)
 
                 if (!IS_ERR_OR_NULL(mm)) {
                         /* ensure this mm_struct can't be freed */
-                        atomic_inc(&mm->mm_count);
+                        mmgrab(mm);
                         /* but do not pin its memory */
                         mmput(mm);
                 }
@@ -1064,7 +1064,7 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy)
                 if (p) {
                         if (atomic_read(&p->mm->mm_users) > 1) {
                                 mm = p->mm;
-                                atomic_inc(&mm->mm_count);
+                                mmgrab(mm);
                         }
                         task_unlock(p);
                 }