On Wed, Jul 19, 2023 at 11:45:26AM -0700, Alexei Starovoitov wrote: > On Wed, Jul 19, 2023 at 7:08 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote: > > > > now task-1 and task-2 share same bpf_trace_nest_level value and same > > 'struct perf_sample_data' buffer on top of &sds->sds[1] > > > > I did not figure out yet the actual exact scenario/cause of the crash yet, > > I suspect one of the tasks copies data over some boundary, but all the > > ideas I had so far did not match the instructions from the crash > > > > anyway I thought that having 2 tasks sharing the same perf_sample_data > > is bad enough to send the patch > > It makes sense now. We forgot to update this part during > transition from preempt_disable to migrate_disable. > > But do you have PREEMPT_RCU in your kernel? yes, I have that enabled and it's also enabled in the kernel that originally hit this > If not then the above race shouldn't be possible. > Worth fixing anyway, of course. > Can you repro with a crafted test? > Multiple uprobes doing bpf_perf_event_output should be enough, right? > For kprobes we're "lucky" due to bpf_prog_active. right, I can reproduce it just with uprobe I realized the changes are on top of bpf-next/master.. I'll rebase it on top of bpf/master and send without RFC tag thanks, jirka
