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 > 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 >
