printk()
supportprintk()
may be called by out-of-band code safely, without encurring
extra latency. The output is conveyed like NMI-originated output,
which involves some delay until the in-band code resumes, and the
console driver(s) can handle it.
Tracepoints can be traversed by out-of-band code safely. Dynamic tracing is available to a kernel running the pipelined interrupt model too.