[PATCH 2/2] change close_files() to use rcu_lock_acquire() to shut up RCU-lockdep

[Oleg Nesterov <oleg@redhat.com>]

put_files_struct() and close_files() do rcu_read_lock() to make
rcu_dereference_check_fdtable() happy.

We can use rcu_lock_acquire(&rcu_lock_map) instead, this looks
self-explanatory and this is nop without CONFIG_DEBUG_LOCK_ALLOC().

While at it, change close_files() to return fdt, this avoids another
rcu_read_lock() + files_fdtable() in put_files_struct().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 fs/file.c |   20 +++++++++-----------
 1 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/fs/file.c b/fs/file.c
index 957cbc0..716d747 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -348,7 +348,7 @@ out:
 	return NULL;
 }
 
-static void close_files(struct files_struct * files)
+static struct fdtable *close_files(struct files_struct * files)
 {
 	int i, j;
 	struct fdtable *fdt;
@@ -358,11 +358,12 @@ static void close_files(struct files_struct * files)
 	/*
 	 * It is safe to dereference the fd table without RCU or
 	 * ->file_lock because this is the last reference to the
-	 * files structure.  But use RCU to shut RCU-lockdep up.
+	 * files structure. But we need to shut RCU-lockdep up.
 	 */
-	rcu_read_lock();
+	rcu_lock_acquire(&rcu_lock_map);
 	fdt = files_fdtable(files);
-	rcu_read_unlock();
+	rcu_lock_release(&rcu_lock_map);
+
 	for (;;) {
 		unsigned long set;
 		i = j * BITS_PER_LONG;
@@ -381,6 +382,8 @@ static void close_files(struct files_struct * files)
 			set >>= 1;
 		}
 	}
+
+	return fdt;
 }
 
 struct files_struct *get_files_struct(struct task_struct *task)
@@ -398,14 +401,9 @@ struct files_struct *get_files_struct(struct task_struct *task)
 
 void put_files_struct(struct files_struct *files)
 {
-	struct fdtable *fdt;
-
 	if (atomic_dec_and_test(&files->count)) {
-		close_files(files);
-		/* not really needed, since nobody can see us */
-		rcu_read_lock();
-		fdt = files_fdtable(files);
-		rcu_read_unlock();
+		struct fdtable *fdt = close_files(files);
+
 		/* free the arrays if they are not embedded */
 		if (fdt != &files->fdtab)
 			__free_fdtable(fdt);
-- 
1.5.5.1