On Fri, Dec 09, 2022 at 02:50:55PM +0100, Jiri Olsa wrote: > On Fri, Dec 09, 2022 at 12:22:37PM +0100, Jiri Olsa wrote: > > SBIP > > > > > > > > > > > > > > > > > I'm trying to understand the severity of the issues and > > > > > > > > whether we need to revert that commit asap since the merge window > > > > > > > > is about to start. > > > > > > > > > > > > > > Jiri, Peter, > > > > > > > > > > > > > > ping. > > > > > > > > > > > > > > cc-ing Thorsten, since he's tracking it now. > > > > > > > > > > > > > > The config has CONFIG_X86_KERNEL_IBT=y. > > > > > > > Is it related? > > > > > > > > > > > > sorry for late reply.. I still did not find the reason, > > > > > > but I did not try with IBT yet, will test now > > > > > > > > > > no difference with IBT enabled, can't reproduce the issue > > > > > > > > > > > > > ok, scratch that.. the reproducer got stuck on wifi init :-\ > > > > > > > > after I fix that I can now reproduce on my local config with > > > > IBT enabled or disabled.. it's something else > > > > > > I'm getting the error also when reverting the static call change, > > > looking for good commit, bisecting > > > > > > I'm getting fail with: > > > f0c4d9fc9cc9 (tag: v6.1-rc4) Linux 6.1-rc4 > > > > > > v6.1-rc1 is ok > > > > so far I narrowed it down between rc1 and rc3.. bisect got me nowhere so far > > > > attaching some more logs > > looking at the code.. how do we ensure that code running through > bpf_prog_run_xdp will not get dispatcher image changed while > it's being exetuted > > we use 'the other half' of the image when we add/remove programs, > but could bpf_dispatcher_update race with bpf_prog_run_xdp like: > > > cpu 0: cpu 1: > > bpf_prog_run_xdp > ... > bpf_dispatcher_xdp_func > start exec image at offset 0x0 > > bpf_dispatcher_update > update image at offset 0x800 > bpf_dispatcher_update > update image at offset 0x0 > > still in image at offset 0x0 > > > that might explain why I wasn't able to trigger that on > bare metal just in qemu I tried patch below and it fixes the issue for me and seems to confirm the race above.. but not sure it's the best fix jirka --- diff --git a/kernel/bpf/dispatcher.c b/kernel/bpf/dispatcher.c index c19719f48ce0..6a2ced102fc7 100644 --- a/kernel/bpf/dispatcher.c +++ b/kernel/bpf/dispatcher.c @@ -124,6 +124,7 @@ static void bpf_dispatcher_update(struct bpf_dispatcher *d, int prev_num_progs) } __BPF_DISPATCHER_UPDATE(d, new ?: (void *)&bpf_dispatcher_nop_func); + synchronize_rcu_tasks(); if (new) d->image_off = noff;
