Hello,
在 2023/11/1 06:06, Alexei Starovoitov 写道:
On Tue, Oct 31, 2023 at 4:38 AM Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx> wrote:
So, maybe another possible solution is:
diff --git a/kernel/bpf/cgroup_iter.c b/kernel/bpf/cgroup_iter.c
index 209e5135f9fb..72a6778e3fba 100644
--- a/kernel/bpf/cgroup_iter.c
+++ b/kernel/bpf/cgroup_iter.c
@@ -282,7 +282,7 @@ static struct bpf_iter_reg bpf_cgroup_reg_info = {
.ctx_arg_info_size = 1,
.ctx_arg_info = {
{ offsetof(struct bpf_iter__cgroup, cgroup),
- PTR_TO_BTF_ID_OR_NULL },
+ PTR_TO_BTF_ID_OR_NULL | MEM_RCU },
},
.seq_info = &cgroup_iter_seq_info,
};
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 59e747938bdb..4fd3f734dffd 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -706,7 +706,7 @@ static struct bpf_iter_reg task_reg_info = {
.ctx_arg_info_size = 1,
.ctx_arg_info = {
{ offsetof(struct bpf_iter__task, task),
- PTR_TO_BTF_ID_OR_NULL },
+ PTR_TO_BTF_ID_OR_NULL | PTR_TRUSTED },
Yep. That looks good.
bpf_cgroup_reg_info -> cgroup is probably PTR_TRUSTED too.
Not sure... why did you go with MEM_RCU there ?
hmm...
That is because in our previous discussion, you suggested we'd better
add BTF_TYPE_SAFE_RCU_OR_NULL(struct bpf_iter__cgroup) {...}
I didn't think too much about it. But I noticed that we only use
cgroup_mutex to protect the iteration in cgroup_iter.c.
Looking at cgroup_kn_lock_live() in kernel/cgroup/cgroup.c, it would use
cgroup_tryget()/cgroup_is_dead() to check whether the cgrp is 'dead'.
cgroup_tryget() seems is equal to bpf_cgroup_acquire(). So, maybe let's
return a 'rcu' cgrp pointer. If BPF Prog want stronger guarantee of
cgrp, just use bpf_cgroup_acquire().
Just some thoughts. Thanks.
