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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