diff options
| author | Tejun Heo <tj@kernel.org> | 2018-04-26 14:29:05 -0700 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2018-04-26 14:29:05 -0700 |
| commit | 9a9e97b2f1f27ec70e3c138a790bd5627747d868 (patch) | |
| tree | 3478f3d670cdde6cd9023990c8ebce2e2ecd73a3 /kernel/cgroup | |
| parent | 8f53470bab04229e93ff9e4c20338cc08b42b344 (diff) | |
cgroup: Add memory barriers to plug cgroup_rstat_updated() race window
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@kernel.org>
Diffstat (limited to 'kernel/cgroup')
| -rw-r--r-- | kernel/cgroup/rstat.c | 16 |
1 files changed, 13 insertions, 3 deletions
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c index 339366e257d4..a4901e20735a 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. @@ -126,6 +129,13 @@ 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; |