cfq-iosched: read_lock() does not always imply rcu_read_lock()

For some configurations of CONFIG_PREEMPT that is not true. So
get rid of __call_for_each_cic() and always uses the explicitly
rcu_read_lock() protected call_for_each_cic() instead.

This fixes a potential bug related to IO scheduler removal or
online switching.

Thanks to Paul McKenney for clarifying this.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 6 insertions, 14 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 46b0a1d1d925..5b52011e3a40 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2582,28 +2582,20 @@ static void cfq_put_queue(struct cfq_queue *cfqq)
 }
 
 /*
- * Must always be called with the rcu_read_lock() held
+ * Call func for each cic attached to this ioc.
  */
 static void
-__call_for_each_cic(struct io_context *ioc,
-                    void (*func)(struct io_context *, struct cfq_io_context *))
+call_for_each_cic(struct io_context *ioc,
+                  void (*func)(struct io_context *, struct cfq_io_context *))
 {
         struct cfq_io_context *cic;
         struct hlist_node *n;
 
+        rcu_read_lock();
+
         hlist_for_each_entry_rcu(cic, n, &ioc->cic_list, cic_list)
                 func(ioc, cic);
-}
 
-/*
- * Call func for each cic attached to this ioc.
- */
-static void
-call_for_each_cic(struct io_context *ioc,
-                  void (*func)(struct io_context *, struct cfq_io_context *))
-{
-        rcu_read_lock();
-        __call_for_each_cic(ioc, func);
         rcu_read_unlock();
 }
 
@@ -2664,7 +2656,7 @@ static void cfq_free_io_context(struct io_context *ioc)
          * should be ok to iterate over the known list, we will see all cic's
          * since no new ones are added.
          */
-        __call_for_each_cic(ioc, cic_free_func);
+        call_for_each_cic(ioc, cic_free_func);
 }
 
 static void cfq_put_cooperator(struct cfq_queue *cfqq)