aboutsummaryrefslogtreecommitdiffstats
path: root/block/cfq-iosched.c
diff options
context:
space:
mode:
authorVivek Goyal <vgoyal@redhat.com>2011-05-19 15:38:22 -0400
committerJens Axboe <jaxboe@fusionio.com>2011-05-20 20:34:52 +0200
commit56edf7d75db5b14d628b46623c414ffbeed68d7f (patch)
tree7d7ff46f03676154d0edf3da85c8e738d506ad92 /block/cfq-iosched.c
parent3e59cf9d66a87763fef6c232a4a8dc664461ca50 (diff)
cfq-iosched: Fix a possible race with cfq cgroup removal code
blkg->key = cfqd is an rcu protected pointer and hence we used to do call_rcu(cfqd->rcu_head) to free up cfqd after one rcu grace period. The problem here is that even though cfqd is around, there are no gurantees that associated request queue (td->queue) or q->queue_lock is still around. A driver might have called blk_cleanup_queue() and release the lock. It might happen that after freeing up the lock we call blkg->key->queue->queue_ock and crash. This is possible in following path. blkiocg_destroy() blkio_unlink_group_fn() cfq_unlink_blkio_group() Hence, wait for an rcu peirod if there are groups which have not been unlinked from blkcg->blkg_list. That way, if there are any groups which are taking cfq_unlink_blkio_group() path, can safely take queue lock. This is how we have taken care of race in throttling logic also. Signed-off-by: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Diffstat (limited to 'block/cfq-iosched.c')
-rw-r--r--block/cfq-iosched.c48
1 files changed, 36 insertions, 12 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index a905b5519ab..e2e6719832e 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -300,7 +300,9 @@ struct cfq_data {
/* List of cfq groups being managed on this device*/
struct hlist_head cfqg_list;
- struct rcu_head rcu;
+
+ /* Number of groups which are on blkcg->blkg_list */
+ unsigned int nr_blkcg_linked_grps;
};
static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd);
@@ -1063,6 +1065,7 @@ static struct cfq_group * cfq_find_alloc_cfqg(struct cfq_data *cfqd,
cfq_blkiocg_add_blkio_group(blkcg, &cfqg->blkg, (void *)cfqd,
0);
+ cfqd->nr_blkcg_linked_grps++;
cfqg->weight = blkcg_get_weight(blkcg, cfqg->blkg.dev);
/* Add group on cfqd list */
@@ -3815,15 +3818,11 @@ static void cfq_put_async_queues(struct cfq_data *cfqd)
cfq_put_queue(cfqd->async_idle_cfqq);
}
-static void cfq_cfqd_free(struct rcu_head *head)
-{
- kfree(container_of(head, struct cfq_data, rcu));
-}
-
static void cfq_exit_queue(struct elevator_queue *e)
{
struct cfq_data *cfqd = e->elevator_data;
struct request_queue *q = cfqd->queue;
+ bool wait = false;
cfq_shutdown_timer_wq(cfqd);
@@ -3842,7 +3841,13 @@ static void cfq_exit_queue(struct elevator_queue *e)
cfq_put_async_queues(cfqd);
cfq_release_cfq_groups(cfqd);
- cfq_blkiocg_del_blkio_group(&cfqd->root_group.blkg);
+
+ /*
+ * If there are groups which we could not unlink from blkcg list,
+ * wait for a rcu period for them to be freed.
+ */
+ if (cfqd->nr_blkcg_linked_grps)
+ wait = true;
spin_unlock_irq(q->queue_lock);
@@ -3852,8 +3857,20 @@ static void cfq_exit_queue(struct elevator_queue *e)
ida_remove(&cic_index_ida, cfqd->cic_index);
spin_unlock(&cic_index_lock);
- /* Wait for cfqg->blkg->key accessors to exit their grace periods. */
- call_rcu(&cfqd->rcu, cfq_cfqd_free);
+ /*
+ * Wait for cfqg->blkg->key accessors to exit their grace periods.
+ * Do this wait only if there are other unlinked groups out
+ * there. This can happen if cgroup deletion path claimed the
+ * responsibility of cleaning up a group before queue cleanup code
+ * get to the group.
+ *
+ * Do not call synchronize_rcu() unconditionally as there are drivers
+ * which create/delete request queue hundreds of times during scan/boot
+ * and synchronize_rcu() can take significant time and slow down boot.
+ */
+ if (wait)
+ synchronize_rcu();
+ kfree(cfqd);
}
static int cfq_alloc_cic_index(void)
@@ -3909,14 +3926,21 @@ static void *cfq_init_queue(struct request_queue *q)
#ifdef CONFIG_CFQ_GROUP_IOSCHED
/*
- * Take a reference to root group which we never drop. This is just
- * to make sure that cfq_put_cfqg() does not try to kfree root group
+ * Set root group reference to 2. One reference will be dropped when
+ * all groups on cfqd->cfqg_list are being deleted during queue exit.
+ * Other reference will remain there as we don't want to delete this
+ * group as it is statically allocated and gets destroyed when
+ * throtl_data goes away.
*/
- cfqg->ref = 1;
+ cfqg->ref = 2;
rcu_read_lock();
cfq_blkiocg_add_blkio_group(&blkio_root_cgroup, &cfqg->blkg,
(void *)cfqd, 0);
rcu_read_unlock();
+ cfqd->nr_blkcg_linked_grps++;
+
+ /* Add group on cfqd->cfqg_list */
+ hlist_add_head(&cfqg->cfqd_node, &cfqd->cfqg_list);
#endif
/*
* Not strictly needed (since RB_ROOT just clears the node and we