On 2024/2/23 12:06, Pu Lehui wrote: > > > On 2024/2/22 16:52, Leon Hwang wrote: [SNIP] >> } >> @@ -575,6 +574,54 @@ static void emit_return(u8 **pprog, u8 *ip) >> *pprog = prog; >> } >> +DEFINE_PER_CPU(u32, bpf_tail_call_cnt); > > Hi Leon, the solution is really simplifies complexity. If I understand > correctly, this TAIL_CALL_CNT becomes the system global wise, not the > prog global wise, but before it was limiting the TCC of entry prog. > Correct. It becomes a PERCPU global variable. But, I think this solution is not robust enough. For example, time prog1 prog1 ==================================> line prog2 this is a time-line on a CPU. If prog1 and prog2 have tailcalls to run, prog2 will reset the tail_call_cnt on current CPU, which is used by prog1. As a result, when the CPU schedules from prog2 to prog1, tail_call_cnt on current CPU has been reset to 0, no matter whether prog1 incremented it. The tail_call_cnt reset issue happens too, even if PERCPU tail_call_cnt moves to 'struct bpf_prog_aux', i.e. one kprobe bpf prog can be triggered on many functions e.g. cilium/pwru. However, this moving is better than this solution. I think, my previous POC of 'struct bpf_prog_run_ctx' would be better. I'll resend it later, with some improvements. Thanks, Leon
