On 6/25/23 4:15 AM, Hou Tao wrote:
Hi,
On 6/24/2023 11:13 AM, Alexei Starovoitov wrote:
From: Alexei Starovoitov <ast@xxxxxxxxxx>
Introduce bpf_mem_[cache_]free_rcu() similar to kfree_rcu().
Unlike bpf_mem_[cache_]free() that links objects for immediate reuse into
per-cpu free list the _rcu() flavor waits for RCU grace period and then moves
objects into free_by_rcu_ttrace list where they are waiting for RCU
task trace grace period to be freed into slab.
SNIP
static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma)
@@ -498,8 +566,8 @@ static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma)
static void free_mem_alloc(struct bpf_mem_alloc *ma)
{
- /* waiting_for_gp_ttrace lists was drained, but __free_rcu might
- * still execute. Wait for it now before we freeing percpu caches.
+ /* waiting_for_gp[_ttrace] lists were drained, but RCU callbacks
+ * might still execute. Wait for them.
*
* rcu_barrier_tasks_trace() doesn't imply synchronize_rcu_tasks_trace(),
* but rcu_barrier_tasks_trace() and rcu_barrier() below are only used
I think an extra rcu_barrier() before rcu_barrier_tasks_trace() is still
needed here, otherwise free_mem_alloc will not wait for inflight
__free_by_rcu() and there will oops in rcu_do_batch().
Agree. I got confused by rcu_trace_implies_rcu_gp().
rcu_barrier() is necessary.
re: draining.
I'll switch to do if (draing) free_all; else call_rcu; scheme
to address potential memory leak though I wasn't able to repro it.
