On Sun, 21 May 2023 10:08:46 +0200 Jiri Olsa <olsajiri@xxxxxxxxx> wrote: > On Sat, May 20, 2023 at 05:47:24PM +0800, Ze Gao wrote: > > > > Hi Jiri, > > > > Would you like to consider to add rcu_is_watching check in > > to solve this from the viewpoint of kprobe_multi_link_prog_run > > I think this was discussed in here: > https://lore.kernel.org/bpf/20230321020103.13494-1-laoar.shao@xxxxxxxxx/ > > and was considered a bug, there's fix mentioned later in the thread > > there's also this recent patchset: > https://lore.kernel.org/bpf/20230517034510.15639-3-zegao@xxxxxxxxxxx/ > > that solves related problems I think this rcu_is_watching() is a bit different issue. This rcu_is_watching() check is required if the kprobe_multi_link_prog_run() uses any RCU API. E.g. rethook_try_get() is also checks rcu_is_watching() because it uses call_rcu(). Thank you, > > > itself? And accounting of missed runs can be added as well > > to imporve observability. > > right, we count fprobe->nmissed but it's not exposed, we should allow > to get 'missed' stats from both fprobe and kprobe_multi later, which > is missing now, will check > > thanks, > jirka > > > > > Regards, > > Ze > > > > > > ----------------- > > From 29fd3cd713e65461325c2703cf5246a6fae5d4fe Mon Sep 17 00:00:00 2001 > > From: Ze Gao <zegao@xxxxxxxxxxx> > > Date: Sat, 20 May 2023 17:32:05 +0800 > > Subject: [PATCH] bpf: kprobe_multi runs bpf progs only when rcu_is_watching > > > > From the perspective of kprobe_multi_link_prog_run, any traceable > > functions can be attached while bpf progs need specical care and > > ought to be under rcu protection. To solve the likely rcu lockdep > > warns once for good, when (future) functions in idle path were > > attached accidentally, we better paying some cost to check at least > > in kernel-side, and return when rcu is not watching, which helps > > to avoid any unpredictable results. > > > > Signed-off-by: Ze Gao <zegao@xxxxxxxxxxx> > > --- > > kernel/trace/bpf_trace.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > > index 9a050e36dc6c..3e6ea7274765 100644 > > --- a/kernel/trace/bpf_trace.c > > +++ b/kernel/trace/bpf_trace.c > > @@ -2622,7 +2622,7 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link, > > struct bpf_run_ctx *old_run_ctx; > > int err; > > > > - if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1)) { > > + if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1 || !rcu_is_watching())) { > > err = 0; > > goto out; > > } > > -- > > 2.40.1 > > -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
