diff options
Diffstat (limited to 'kernel/bpf/cpumap.c')
| -rw-r--r-- | kernel/bpf/cpumap.c | 116 |
1 files changed, 35 insertions, 81 deletions
diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c index 286ab3db0fde..e42a1bdb7f53 100644 --- a/kernel/bpf/cpumap.c +++ b/kernel/bpf/cpumap.c @@ -61,8 +61,6 @@ struct bpf_cpu_map_entry { /* XDP can run multiple RX-ring queues, need __percpu enqueue store */ struct xdp_bulk_queue __percpu *bulkq; - struct bpf_cpu_map *cmap; - /* Queue with potential multi-producers, and single-consumer kthread */ struct ptr_ring *queue; struct task_struct *kthread; @@ -70,11 +68,8 @@ struct bpf_cpu_map_entry { struct bpf_cpumap_val value; struct bpf_prog *prog; - atomic_t refcnt; /* Control when this struct can be free'ed */ - struct rcu_head rcu; - - struct work_struct kthread_stop_wq; struct completion kthread_running; + struct rcu_work free_work; }; struct bpf_cpu_map { @@ -119,11 +114,6 @@ static struct bpf_map *cpu_map_alloc(union bpf_attr *attr) return &cmap->map; } -static void get_cpu_map_entry(struct bpf_cpu_map_entry *rcpu) -{ - atomic_inc(&rcpu->refcnt); -} - static void __cpu_map_ring_cleanup(struct ptr_ring *ring) { /* The tear-down procedure should have made sure that queue is @@ -144,35 +134,6 @@ static void __cpu_map_ring_cleanup(struct ptr_ring *ring) } } -static void put_cpu_map_entry(struct bpf_cpu_map_entry *rcpu) -{ - if (atomic_dec_and_test(&rcpu->refcnt)) { - if (rcpu->prog) - bpf_prog_put(rcpu->prog); - /* The queue should be empty at this point */ - __cpu_map_ring_cleanup(rcpu->queue); - ptr_ring_cleanup(rcpu->queue, NULL); - kfree(rcpu->queue); - kfree(rcpu); - } -} - -/* called from workqueue, to workaround syscall using preempt_disable */ -static void cpu_map_kthread_stop(struct work_struct *work) -{ - struct bpf_cpu_map_entry *rcpu; - - rcpu = container_of(work, struct bpf_cpu_map_entry, kthread_stop_wq); - - /* Wait for flush in __cpu_map_entry_free(), via full RCU barrier, - * as it waits until all in-flight call_rcu() callbacks complete. - */ - rcu_barrier(); - - /* kthread_stop will wake_up_process and wait for it to complete */ - kthread_stop(rcpu->kthread); -} - static void cpu_map_bpf_prog_run_skb(struct bpf_cpu_map_entry *rcpu, struct list_head *listp, struct xdp_cpumap_stats *stats) @@ -397,7 +358,6 @@ static int cpu_map_kthread_run(void *data) } __set_current_state(TASK_RUNNING); - put_cpu_map_entry(rcpu); return 0; } @@ -474,9 +434,6 @@ __cpu_map_entry_alloc(struct bpf_map *map, struct bpf_cpumap_val *value, if (IS_ERR(rcpu->kthread)) goto free_prog; - get_cpu_map_entry(rcpu); /* 1-refcnt for being in cmap->cpu_map[] */ - get_cpu_map_entry(rcpu); /* 1-refcnt for kthread */ - /* Make sure kthread runs on a single CPU */ kthread_bind(rcpu->kthread, cpu); wake_up_process(rcpu->kthread); @@ -503,40 +460,40 @@ free_rcu: return NULL; } -static void __cpu_map_entry_free(struct rcu_head *rcu) +static void __cpu_map_entry_free(struct work_struct *work) { struct bpf_cpu_map_entry *rcpu; /* This cpu_map_entry have been disconnected from map and one - * RCU grace-period have elapsed. Thus, XDP cannot queue any + * RCU grace-period have elapsed. Thus, XDP cannot queue any * new packets and cannot change/set flush_needed that can * find this entry. */ - rcpu = container_of(rcu, struct bpf_cpu_map_entry, rcu); + rcpu = container_of(to_rcu_work(work), struct bpf_cpu_map_entry, free_work); + /* kthread_stop will wake_up_process and wait for it to complete. + * cpu_map_kthread_run() makes sure the pointer ring is empty + * before exiting. + */ + kthread_stop(rcpu->kthread); + + if (rcpu->prog) + bpf_prog_put(rcpu->prog); + /* The queue should be empty at this point */ + __cpu_map_ring_cleanup(rcpu->queue); + ptr_ring_cleanup(rcpu->queue, NULL); + kfree(rcpu->queue); free_percpu(rcpu->bulkq); - /* Cannot kthread_stop() here, last put free rcpu resources */ - put_cpu_map_entry(rcpu); + kfree(rcpu); } -/* After xchg pointer to bpf_cpu_map_entry, use the call_rcu() to - * ensure any driver rcu critical sections have completed, but this - * does not guarantee a flush has happened yet. Because driver side - * rcu_read_lock/unlock only protects the running XDP program. The - * atomic xchg and NULL-ptr check in __cpu_map_flush() makes sure a - * pending flush op doesn't fail. - * - * The bpf_cpu_map_entry is still used by the kthread, and there can - * still be pending packets (in queue and percpu bulkq). A refcnt - * makes sure to last user (kthread_stop vs. call_rcu) free memory - * resources. - * - * The rcu callback __cpu_map_entry_free flush remaining packets in - * percpu bulkq to queue. Due to caller map_delete_elem() disable - * preemption, cannot call kthread_stop() to make sure queue is empty. - * Instead a work_queue is started for stopping kthread, - * cpu_map_kthread_stop, which waits for an RCU grace period before - * stopping kthread, emptying the queue. +/* After the xchg of the bpf_cpu_map_entry pointer, we need to make sure the old + * entry is no longer in use before freeing. We use queue_rcu_work() to call + * __cpu_map_entry_free() in a separate workqueue after waiting for an RCU grace + * period. This means that (a) all pending enqueue and flush operations have + * completed (because of the RCU callback), and (b) we are in a workqueue + * context where we can stop the kthread and wait for it to exit before freeing + * everything. */ static void __cpu_map_entry_replace(struct bpf_cpu_map *cmap, u32 key_cpu, struct bpf_cpu_map_entry *rcpu) @@ -545,9 +502,8 @@ static void __cpu_map_entry_replace(struct bpf_cpu_map *cmap, old_rcpu = unrcu_pointer(xchg(&cmap->cpu_map[key_cpu], RCU_INITIALIZER(rcpu))); if (old_rcpu) { - call_rcu(&old_rcpu->rcu, __cpu_map_entry_free); - INIT_WORK(&old_rcpu->kthread_stop_wq, cpu_map_kthread_stop); - schedule_work(&old_rcpu->kthread_stop_wq); + INIT_RCU_WORK(&old_rcpu->free_work, __cpu_map_entry_free); + queue_rcu_work(system_wq, &old_rcpu->free_work); } } @@ -559,7 +515,7 @@ static long cpu_map_delete_elem(struct bpf_map *map, void *key) if (key_cpu >= map->max_entries) return -EINVAL; - /* notice caller map_delete_elem() use preempt_disable() */ + /* notice caller map_delete_elem() uses rcu_read_lock() */ __cpu_map_entry_replace(cmap, key_cpu, NULL); return 0; } @@ -595,7 +551,6 @@ static long cpu_map_update_elem(struct bpf_map *map, void *key, void *value, rcpu = __cpu_map_entry_alloc(map, &cpumap_value, key_cpu); if (!rcpu) return -ENOMEM; - rcpu->cmap = cmap; } rcu_read_lock(); __cpu_map_entry_replace(cmap, key_cpu, rcpu); @@ -611,16 +566,15 @@ static void cpu_map_free(struct bpf_map *map) /* At this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0, * so the bpf programs (can be more than one that used this map) were * disconnected from events. Wait for outstanding critical sections in - * these programs to complete. The rcu critical section only guarantees - * no further "XDP/bpf-side" reads against bpf_cpu_map->cpu_map. - * It does __not__ ensure pending flush operations (if any) are - * complete. + * these programs to complete. synchronize_rcu() below not only + * guarantees no further "XDP/bpf-side" reads against + * bpf_cpu_map->cpu_map, but also ensure pending flush operations + * (if any) are completed. */ - synchronize_rcu(); - /* For cpu_map the remote CPUs can still be using the entries - * (struct bpf_cpu_map_entry). + /* The only possible user of bpf_cpu_map_entry is + * cpu_map_kthread_run(). */ for (i = 0; i < cmap->map.max_entries; i++) { struct bpf_cpu_map_entry *rcpu; @@ -629,8 +583,8 @@ static void cpu_map_free(struct bpf_map *map) if (!rcpu) continue; - /* bq flush and cleanup happens after RCU grace-period */ - __cpu_map_entry_replace(cmap, i, NULL); /* call_rcu */ + /* Stop kthread and cleanup entry directly */ + __cpu_map_entry_free(&rcpu->free_work.work); } bpf_map_area_free(cmap->cpu_map); bpf_map_area_free(cmap); |