LTTng

We start the tracing with:

lttng create xxx_trace --snapshot --no-output
lttng enable-channel xxx_ktrace -s xxx_trace -k --subbuf-size=256k --num-subbuf=16
lttng enable-event -s xxx_trace -c xxx_ktrace -k sched_switch,irq_handler_entry,irq_handler_exit,softirq_entry,softirq_exit,softirq_raise
lttng enable-event -s xxx_trace -c xxx_ktrace -k --syscall restart_syscall,exit,read,write,open,close,execve,ioctl,fcntl,ptrace,mmap,munmap,fs
lttng start xxx_trace

Then we do reboot application, without rebooting the kernel, we start tracing again with same commands as above, without using lttng-stop, or lttng-destroy.

We always get the following output:

2023-09-21T11:39:49.534934+00:00 Error: Session name already exists
2023-09-21T11:39:49.538108+00:00 Error: Channel xxx_ktrace: Tracing has already been started once (session xxx_trace)
2023-09-21T11:39:49.540223+00:00 Error: Event sched_switch: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.540388+00:00 Error: Event irq_handler_entry: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.545139+00:00 Error: Event irq_handler_exit: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.545881+00:00 Error: Event softirq_entry: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.546041+00:00 Error: Event softirq_exit: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.546161+00:00 Error: Event softirq_raise: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.548267+00:00 Error: Event restart_syscall: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.548357+00:00 Error: Event exit: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.548458+00:00 Error: Event read: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.548549+00:00 Error: Event write: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.548634+00:00 Error: Event open: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.548720+00:00 Error: Event close: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.548804+00:00 Error: Event execve: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.548930+00:00 Error: Event ioctl: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.549027+00:00 Error: Event fcntl: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.549118+00:00 Error: Event ptrace: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.549204+00:00 Error: Event mmap: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.549289+00:00 Error: Event munmap: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)
2023-09-21T11:39:49.549374+00:00 Error: Event fs: The command tried to enable an event in a new domain for a session that has already been started once. (channel xxx_ktrace, session xxx_trace)

This is expected.

But the problem is that sometime, not always, above errors are followed by this assert error:

2023-09-21T11:39:49.592244+00:00 lttng-sessiond: ../../../../git/src/bin/lttng-sessiond/client.c:2678: thread_manage_clients: Assertion `cmd_ctx.reply_payload.buffer.size >= sizeof(*llm)' failed.
2023-09-21T11:39:49.592258+00:00 Tracing started for session xxx_trace

and consequently lttng-sessiond process aborts.

What is causing assert error at lttng-sessiond/client.c:2678? Can starting same session name without stop, or destroy, lead to this assert error? We did not experience `cmd_ctx.reply_payload.buffer.size >= sizeof(*llm)' asserts with previous versions of lttng.

version info:

lttng-tools 2.13.9
lttng-ust 2.13.5
lttng-ust212 2.12.6

architecture:
x86, Intel Atom 12 cores

OS version:
Linux version 5.10.176