Merge branch 'merge' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc

[cascardo/linux.git] / block / blk-cgroup.c

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index e4a4145..1039fb9 100644 (file)
--- 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);
 
        /*