diff options
Diffstat (limited to 'kernel/cgroup/rstat.c')
| -rw-r--r-- | kernel/cgroup/rstat.c | 13 |
1 files changed, 8 insertions, 5 deletions
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c index a198e40c799b..150e5871e66f 100644 --- a/kernel/cgroup/rstat.c +++ b/kernel/cgroup/rstat.c @@ -71,7 +71,6 @@ __bpf_kfunc void css_rstat_updated(struct cgroup_subsys_state *css, int cpu) { struct llist_head *lhead; struct css_rstat_cpu *rstatc; - struct css_rstat_cpu __percpu *rstatc_pcpu; struct llist_node *self; /* @@ -104,18 +103,22 @@ __bpf_kfunc void css_rstat_updated(struct cgroup_subsys_state *css, int cpu) /* * This function can be renentered by irqs and nmis for the same cgroup * and may try to insert the same per-cpu lnode into the llist. Note - * that llist_add() does not protect against such scenarios. + * that llist_add() does not protect against such scenarios. In addition + * this same per-cpu lnode can be modified through init_llist_node() + * from css_rstat_flush() running on a different CPU. * * To protect against such stacked contexts of irqs/nmis, we use the * fact that lnode points to itself when not on a list and then use - * this_cpu_cmpxchg() to atomically set to NULL to select the winner + * try_cmpxchg() to atomically set to NULL to select the winner * which will call llist_add(). The losers can assume the insertion is * successful and the winner will eventually add the per-cpu lnode to * the llist. + * + * Please note that we can not use this_cpu_cmpxchg() here as on some + * archs it is not safe against modifications from multiple CPUs. */ self = &rstatc->lnode; - rstatc_pcpu = css->rstat_cpu; - if (this_cpu_cmpxchg(rstatc_pcpu->lnode.next, self, NULL) != self) + if (!try_cmpxchg(&rstatc->lnode.next, &self, NULL)) return; lhead = ss_lhead_cpu(css->ss, cpu); |