cgroup_rstat_updated() has a small race window where an updated signaling can race with flush and could be lost till the next update. This wasn't a problem for the existing usages, but we plan to use rstat to track counters which need to be accurate. This patch plugs the race window by synchronizing cgroup_rstat_updated() and flush path with memory barriers around cgroup_rstat_cpu->updated_next pointer. Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> --- kernel/cgroup/rstat.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c index 18b464a..662d7ae 100644 --- a/kernel/cgroup/rstat.c +++ b/kernel/cgroup/rstat.c @@ -28,9 +28,12 @@ void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) unsigned long flags; /* - * Speculative already-on-list test. This may race leading to - * temporary inaccuracies, which is fine. - * + * Paired with the one in cgroup_rstat_cpu_pop_upated(). Either we + * see NULL updated_next or they see our updated stat. + */ + smp_mb(); + + /* * Because @parent's updated_children is terminated with @parent * instead of NULL, we can tell whether @cgrp is on the list by * testing the next pointer for NULL. @@ -125,6 +128,13 @@ static struct cgroup *cgroup_rstat_cpu_pop_updated(struct cgroup *pos, *nextp = rstatc->updated_next; rstatc->updated_next = NULL; + + /* + * Paired with the one in cgroup_rstat_cpu_updated(). + * Either they see NULL updated_next or we see their + * updated stat. + */ + smp_mb(); } return pos; -- 2.9.5 -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
