blk-cgroup: Make cgroup stat reset path blkg->lock free for dispatch stats

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

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 3622518..e41cc6f 100644 (file)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -537,6 +537,30 @@ struct blkio_group *blkiocg_lookup_group(struct blkio_cgroup *blkcg, void *key)
 }
 EXPORT_SYMBOL_GPL(blkiocg_lookup_group);
 
+static void blkio_reset_stats_cpu(struct blkio_group *blkg)
+{
+       struct blkio_group_stats_cpu *stats_cpu;
+       int i, j, k;
+       /*
+        * Note: On 64 bit arch this should not be an issue. This has the
+        * possibility of returning some inconsistent value on 32bit arch
+        * as 64bit update on 32bit is non atomic. Taking care of this
+        * corner case makes code very complicated, like sending IPIs to
+        * cpus, taking care of stats of offline cpus etc.
+        *
+        * reset stats is anyway more of a debug feature and this sounds a
+        * corner case. So I am not complicating the code yet until and
+        * unless this becomes a real issue.
+        */
+       for_each_possible_cpu(i) {
+               stats_cpu = per_cpu_ptr(blkg->stats_cpu, i);
+               stats_cpu->sectors = 0;
+               for(j = 0; j < BLKIO_STAT_CPU_NR; j++)
+                       for (k = 0; k < BLKIO_STAT_TOTAL; k++)
+                               stats_cpu->stat_arr_cpu[j][k] = 0;
+       }
+}
+
 static int
 blkiocg_reset_stats(struct cgroup *cgroup, struct cftype *cftype, u64 val)
 {
@@ -581,7 +605,11 @@ blkiocg_reset_stats(struct cgroup *cgroup, struct cftype *cftype, u64 val)
                }
 #endif
                spin_unlock(&blkg->stats_lock);
+
+               /* Reset Per cpu stats which don't take blkg->stats_lock */
+               blkio_reset_stats_cpu(blkg);
        }
+
        spin_unlock_irq(&blkcg->lock);
        return 0;
 }