mm: use mmget_not_zero() helper

We already have the helper, we can convert the rest of the kernel
mechanically using:

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

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

Link: http://lkml.kernel.org/r/20161218123229.22952-3-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>

fs/proc/base.c

@@ -813,7 +813,7 @@ static ssize_t mem_rw(struct file *file, char __user *buf,
 		return -ENOMEM;
 
 	copied = 0;
-	if (!atomic_inc_not_zero(&mm->mm_users))
+	if (!mmget_not_zero(mm))
 		goto free;
 
 	/* Maybe we should limit FOLL_FORCE to actual ptrace users? */
@@ -921,7 +921,7 @@ static ssize_t environ_read(struct file *file, char __user *buf,
 		return -ENOMEM;
 
 	ret = 0;
-	if (!atomic_inc_not_zero(&mm->mm_users))
+	if (!mmget_not_zero(mm))
 		goto free;
 
 	down_read(&mm->mmap_sem);

fs/proc/task_mmu.c

@@ -167,7 +167,7 @@ static void *m_start(struct seq_file *m, loff_t *ppos)
 		return ERR_PTR(-ESRCH);
 
 	mm = priv->mm;
-	if (!mm || !atomic_inc_not_zero(&mm->mm_users))
+	if (!mm || !mmget_not_zero(mm))
 		return NULL;
 
 	down_read(&mm->mmap_sem);
@@ -1352,7 +1352,7 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
 	unsigned long end_vaddr;
 	int ret = 0, copied = 0;
 
-	if (!mm || !atomic_inc_not_zero(&mm->mm_users))
+	if (!mm || !mmget_not_zero(mm))
 		goto out;
 
 	ret = -EINVAL;

fs/proc/task_nommu.c

@@ -219,7 +219,7 @@ static void *m_start(struct seq_file *m, loff_t *pos)
 		return ERR_PTR(-ESRCH);
 
 	mm = priv->mm;
-	if (!mm || !atomic_inc_not_zero(&mm->mm_users))
+	if (!mm || !mmget_not_zero(mm))
 		return NULL;
 
 	down_read(&mm->mmap_sem);