On 08/26/2016 09:58 PM, Daniel Mack wrote:
This patch adds two sets of eBPF program pointers to struct cgroup.
One for such that are directly pinned to a cgroup, and one for such
that are effective for it.
To illustrate the logic behind that, assume the following example
cgroup hierarchy.
A - B - C
\ D - E
If only B has a program attached, it will be effective for B, C, D
and E. If D then attaches a program itself, that will be effective for
both D and E, and the program in B will only affect B and C. Only one
program of a given type is effective for a cgroup.
Attaching and detaching programs will be done through the bpf(2)
syscall. For now, ingress and egress inet socket filtering are the
only supported use-cases.
Signed-off-by: Daniel Mack <dan...@zonque.org>
[...]
+void __cgroup_bpf_update(struct cgroup *cgrp,
+ struct cgroup *parent,
+ struct bpf_prog *prog,
+ enum bpf_attach_type type)
+{
+ struct bpf_prog *old_prog, *effective;
+ struct cgroup_subsys_state *pos;
+
+ old_prog = xchg(cgrp->bpf.prog + type, prog);
+
+ if (prog)
+ static_branch_inc(&cgroup_bpf_enabled_key);
+
+ if (old_prog) {
+ bpf_prog_put(old_prog);
+ static_branch_dec(&cgroup_bpf_enabled_key);
+ }
+
+ effective = (!prog && parent) ?
+ rcu_dereference_protected(parent->bpf.effective[type],
+ lockdep_is_held(&cgroup_mutex)) :
+ prog;
+
+ css_for_each_descendant_pre(pos, &cgrp->self) {
+ struct cgroup *desc = container_of(pos, struct cgroup, self);
+
+ /* skip the subtree if the descendant has its own program */
+ if (desc->bpf.prog[type] && desc != cgrp)
+ pos = css_rightmost_descendant(pos);
+ else
+ rcu_assign_pointer(desc->bpf.effective[type],
+ effective);
+ }
Shouldn't the old_prog reference only be released right here at the end
instead of above (otherwise this could race)?
+}
