Hi, On 7/21/2023 8:44 PM, Jiri Olsa wrote: > On Fri, Jul 21, 2023 at 08:12:41PM +0800, Hou Tao wrote: >> >> On 7/20/2023 4:57 PM, Jiri Olsa wrote: >>> hi, >>> we got report of kernel crash [1][3] within bpf_event_output helper. >>> >>> The reason is the nesting protection code in bpf_event_output that expects >>> disabled preemption, which is not guaranteed for programs executed by >>> bpf_prog_run_array_cg. >>> >>> I managed to reproduce on tracing side where we have the same problem >>> in bpf_perf_event_output. The reproducer [2] just creates busy uprobe >>> and call bpf_perf_event_output helper a lot. >> It is a little strange that I can not reproduce the same problem on my >> local VM by using the same reproducer from [2]. I have already enabled >> both CONFIG_PREEMPT=y and CONFIG_PREEMPT_RCU=y. > I have 4 cpu VM and I run '# ./test_progs -t krava -v' together with test > instance for each of cpu, like: > > # ./test & ./test & ./test & ./test & > > and it's hit within 15 minutes > > attaching my config so you can compare, but can't think of another > option you need By using my .config, the reproduce just cost about 2 hours. I will try your .config to see whether or not there is any difference. > > >>> v2 changes: >>> - I changed 'Fixes' commits to where I saw we switched from preempt_disable >>> to migrate_disable, but I'm not completely sure about the patch 2, because >>> it was tricky to find, would be nice if somebody could check on that >> After digging into the change log, I think the fix tag is correct. In >> commit 2a916f2f546c, preempt_disable() is changed to migrate_disable() >> in the macro BPF_PROG_RUN_ARRAY(), and in commit 772412176fb9, >> BPF_PROG_RUN_ARRAY_FLAGS() was added for >> __cgroup_bpf_run_filter_sock_addr() and the implementation of >> BPF_PROG_RUN_ARRAY_FLAGS() was basically copied from >> BPF_PROG_RUN_ARRAY(). And afterwards, BPF_PROG_RUN_ARRAY_FLAGS was >> rename to BPF_PROG_RUN_ARRAY_CG_FLAGS, then >> bpf_prog_run_array_cg_flags(), and was renamed to >> bpf_prog_run_array_cg() in the final. > thanks for checking on that You are welcome. Hope it is helpful. Regards, Hou > > jirka >
