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>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 46b0a1d..5b52011 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2582,28 +2582,20 @@
}
/*
- * Must always be called with the rcu_read_lock() held
- */
-static void
-__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;
-
- 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 *))
{
+ struct cfq_io_context *cic;
+ struct hlist_node *n;
+
rcu_read_lock();
- __call_for_each_cic(ioc, func);
+
+ hlist_for_each_entry_rcu(cic, n, &ioc->cic_list, cic_list)
+ func(ioc, cic);
+
rcu_read_unlock();
}
@@ -2664,7 +2656,7 @@
* 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)