Re: ~90s shutdown delay with v6.19 and PREEMPT_RT

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 24 Feb 2026 00:36:27 +0100
Bert Karwatzki <spasswolf@web.de> wrote:

> As the bisection in suggested that commit9311e6c29b34 ("cgroup: Fix sleeping from invalid context warning on PREEMPT_RT")
> is somehow causing the problem I put some printk()s in the code changed by this
> commit and captured the output via netconsole (I tried using trace_printk() to
> use the persistent ringbuffer but got no output).

It's described in the document I posted:

   https://docs.kernel.org/trace/debugging.html

    Using trace_printk() in the boot instance

    By default, the content of trace_printk() goes into the top level
    tracing instance. But this instance is never preserved across
    boots. To have the trace_printk() content, and some other internal
    tracing go to the preserved buffer (like dump stacks), either set
    the instance to be the trace_printk() destination from the kernel
    command line, or set it after boot up via the trace_printk_dest
    option.

    After boot up:

    echo 1 > /sys/kernel/tracing/instances/boot_map/options/trace_printk_dest

    From the kernel command line:

    reserve_mem=12M:4096:trace trace_instance=boot_map^traceprintk^traceoff@trace

    If setting it from the kernel command line, it is recommended to
    also disable tracing with the “traceoff” flag, and enable tracing
    after boot up. Otherwise the trace from the most recent boot will
    be mixed with the trace from the previous boot, and may make it
    confusing to read.

-- Steve