| Hello everyone, I am currently working on my bachelor thesis and I have a question regarding PIDs/TGIDs in the sunrpc layer of the kernel. I was wondering if I can obtain the PID/TGID of the userland process that originally caused a RPC request to be transmitted, from within the RPC request itself. Here is what I did: With a BPF program I collect the following metrics from a tracepoint inside “xprt_request_transmit()” function defined in /net/sunrpc/xprt.c: 1. current task name 2. current PID/TGID as a return value of bpf_get_current_pid_tgid() 3. The TGID assigned in the tk_owner field of struct rpc_task. (Using: BPF_CORE_READ(rpc_rqst, rq_task, tk_owner)) From the sources I have learned that TGID from 3. is assigned in “rpc_init_task() function” defined in /net/sunrpc/sched.c: task->tk_owner = current->tgid; In the output of the BPF program I see records with the following entries for the above metrics: 1. "kworker/u389:3” 2. "PID": 455045, "TGID": 455045 3. "rpc_tk_owner_tgid": 3989219 Here, evidently, the thread that executes the "xprt_request_transmit()” differs from the one that assigned the rpc_tk_owner_tgid in “rpc_init_task()”. The latter was executed by the userland process. But there are also records like this: 1. "kworker/u128:4" 2. "PID": 1457360, "TGID": 1457360 3. "rpc_tk_owner_tgid": 1457360 Here, the kworker did both the jobs. Now to my questions: 1. What determines which thread executes rpc_init_task()? 2. How can I, with certainty, obtain the userland process’ PID/TGID from inside rpc_init_task() ? Thank you for your answers. Best regards, Sandro |
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