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-rw-r--r--block/blk-cgroup.c15
1 files changed, 14 insertions, 1 deletions
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index e4a4145926f6..1039fb9ff5f5 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -451,7 +451,20 @@ static int blkcg_reset_stats(struct cgroup_subsys_state *css,
struct blkcg_gq *blkg;
int i;
- mutex_lock(&blkcg_pol_mutex);
+ /*
+ * XXX: We invoke cgroup_add/rm_cftypes() under blkcg_pol_mutex
+ * which ends up putting cgroup's internal cgroup_tree_mutex under
+ * it; however, cgroup_tree_mutex is nested above cgroup file
+ * active protection and grabbing blkcg_pol_mutex from a cgroup
+ * file operation creates a possible circular dependency. cgroup
+ * internal locking is planned to go through further simplification
+ * and this issue should go away soon. For now, let's trylock
+ * blkcg_pol_mutex and restart the write on failure.
+ *
+ * http://lkml.kernel.org/g/5363C04B.4010400@oracle.com
+ */
+ if (!mutex_trylock(&blkcg_pol_mutex))
+ return restart_syscall();
spin_lock_irq(&blkcg->lock);
/*