MMU notifier: use the new mmap locking API

This use is converted manually ahead of the next patch in the series, as
it requires including a new header which the automated conversion would
miss.

Signed-off-by: Michel Lespinasse <walken@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Laurent Dufour <ldufour@linux.ibm.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Liam Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ying Han <yinghan@google.com>
Link: http://lkml.kernel.org/r/20200520052908.204642-3-walken@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mmu_notifier.h

@@ -5,6 +5,7 @@
 #include <linux/list.h>
 #include <linux/spinlock.h>
 #include <linux/mm_types.h>
+#include <linux/mmap_lock.h>
 #include <linux/srcu.h>
 #include <linux/interval_tree.h>
 
@@ -277,9 +278,9 @@ mmu_notifier_get(const struct mmu_notifier_ops *ops, struct mm_struct *mm)
 {
 	struct mmu_notifier *ret;
 
-	down_write(&mm->mmap_sem);
+	mmap_write_lock(mm);
 	ret = mmu_notifier_get_locked(ops, mm);
-	up_write(&mm->mmap_sem);
+	mmap_write_unlock(mm);
 	return ret;
 }
 void mmu_notifier_put(struct mmu_notifier *subscription);