mm/memory-failure: share the i_mmap_rwsem

No brainer conversion: collect_procs_file() only schedules a process for
later kill, share the lock, similarly to the anon vma variant.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: "Kirill A. Shutemov" <kirill@shutemov.name>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory-failure.c

@@ -466,7 +466,7 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
 	struct task_struct *tsk;
 	struct address_space *mapping = page->mapping;
 
-	i_mmap_lock_write(mapping);
+	i_mmap_lock_read(mapping);
 	read_lock(&tasklist_lock);
 	for_each_process(tsk) {
 		pgoff_t pgoff = page_to_pgoff(page);
@@ -488,7 +488,7 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
 		}
 	}
 	read_unlock(&tasklist_lock);
-	i_mmap_unlock_write(mapping);
+	i_mmap_unlock_read(mapping);
 }
 
 /*