On 27/8/25 10:23, Alexei Starovoitov wrote: > On Tue, Aug 26, 2025 at 7:13 PM Leon Hwang <leon.hwang@xxxxxxxxx> wrote: >> >> Hi, >> >> I’ve encountered a reproducible deadlock while developing the funcgraph >> feature for bpfsnoop [0]. > > debug it pls. It’s quite difficult for me. I’ve tried debugging it but didn’t succeed. > Sounds like you're implying that the root cause is in bpf, > but why do you think so? > > You're attaching to things that shouldn't be attached to. > Like rcu_lockdep_current_cpu_online() > so effectively you're recursing in that lockdep code. > See big lock there. It will dead lock for sure. If a function that acquires a lock can be traced by a tracing program, bpfsnoop’s funcgraph will attempt to trace it as well. In such cases, a deadlock is highly likely to occur. With bpfsnoop I try my best to avoid such deadlock issues. But what about other bpf tracing tools? If they don’t handle this properly, the kernel is very likely to crash. Thanks, Leon
