mm, counters: remove task argument to sync_mm_rss() and __sync_task_rss_stat()

sync_mm_rss() can only be used for current to avoid race conditions in
iterating and clearing its per-task counters.  Remove the task argument
for it and its helper function, __sync_task_rss_stat(), to avoid thinking
it can be used safely for anything other than current.

Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/mmu_context.c b/mm/mmu_context.c
index cf332bc0..3dcfaf4 100644
--- a/mm/mmu_context.c
+++ b/mm/mmu_context.c
@@ -53,7 +53,7 @@
 	struct task_struct *tsk = current;
 
 	task_lock(tsk);
-	sync_mm_rss(tsk, mm);
+	sync_mm_rss(mm);
 	tsk->mm = NULL;
 	/* active_mm is still 'mm' */
 	enter_lazy_tlb(mm, tsk);