On Mon, Feb 14, 2022 at 12:23 PM Hao Luo <haoluo@xxxxxxxxxx> wrote: > > On Mon, Feb 14, 2022 at 11:25 AM Alexei Starovoitov > <alexei.starovoitov@xxxxxxxxx> wrote: > > > > On Mon, Feb 14, 2022 at 10:29 AM Hao Luo <haoluo@xxxxxxxxxx> wrote: > > > Hi Alexei, > > > > > > Actually, I found this almost worked, except that the tracepoints > > > cgroup_mkdir and cgroup_rmdir are not sleepable. They are inside a > > > spinlock's critical section with irq off. I guess one solution is to > > > offload the sleepable part of the bpf prog into a thread context. We > > > may create a dedicated kernel thread or use workqueue for this. Do you > > > have any advice? > > > > Are you referring to spin_lock in TRACE_CGROUP_PATH > > that protects global trace_cgroup_path[] buffer? > > Yes, that's the spin_lock I am talking about. > > > That is fixable. > > Do you actually need the string path returned by cgroup_path() in bpf prog? > > Maybe prog can call cgroup_path() by itself when necessary. > > Parsing strings isn't great anyway. The bpf prog probably needs the last > > part of the dir only. So cgrp->kn->name would do it? > > The TRACE_CGROUP_PATH wasn't designed to be turned on 24/7. > > That global spin_lock is not great for production use. > > No need to delegate sleepable bpf to thread context. > > Let's refactor that tracepoint a bit. > > No, we don't need cgroup_path(). We are going to name the directories > by cgrp->kn->id. I can add a fast version for cgroup_xxx tracepoints, > which don't require the full path and can be turned on 24/7. Sounds good. We need a flag for tracepoints anyway to indicate which ones are sleepable. Probably similar to what we did for DEFINE_EVENT_WRITABLE.
