cfq-iosched: fix RCU race in the cfq io_context destructor handling
put_io_context() drops the RCU read lock before calling into cfq_dtor(),
however we need to hold off freeing there before grabbing and
dereferencing the first object on the list.
So extend the rcu_read_lock() scope to cover the calling of cfq_dtor(),
and optimize cfq_free_io_context() to use a new variant for
call_for_each_cic() that assumes the RCU read lock is already held.
Hit in the wild by Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index f4e1006..7f909d2 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1142,6 +1142,17 @@
kmem_cache_free(cfq_pool, cfqq);
}
+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.
*/
@@ -1149,12 +1160,8 @@
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_for_each_cic(ioc, func);
rcu_read_unlock();
}
@@ -1198,7 +1205,7 @@
* 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_exit_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq)