On 2022-06-21, "Paul E. McKenney" <paulmck@xxxxxxxxxx> wrote:
> The patch below will cause rcutorture to implicitly test this
> functionality, unless told otherwise, for example, by using the
> --bootargs "torture.printk_shutdown_bug_workaround" kvm.sh
> argument.
>
> Thoughts?
I feel like this is dirtying the torture.* bootarg namespace a
bit. Also, I am not sure how useful it is as a dynamic option. I assume
that users would generally avoid using it, so its very existence might
just be more noise in the documentation and code. It is an unusual
feature:
"In case some bug shows up, here is a flag to avoid it."
I personally would just drop the patch and rely on a correctly
functional kernel. But I am also not an rcutorture user. If _you_ think
that such a flag is useful, feel free to include the patch.
> commit 204bf1e2a5a2fb68c15b4b64793ad0896db6f705
> Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Date: Tue Jun 21 11:02:25 2022 -0700
>
> torture: Optionally flush printk() buffers before powering off
>
> The rcutorture test suite produces quite a bit of console output at
> the end of a test. This means that the new-in-2022 printk() kthreads
> are likely to be in the process of flushing output at the time of the
> torture_shutdown() function's call to kernel_power_off(). Normally,
> rcutorture relies on printk() to flush any pending output upon shutdown,
> the better to detect bugs in this area, for example, the one introduced
> by 8e274732115f ("printk: extend console_lock for per-console locking").
> However, once such a bug is detected and reported, it is necessary to
> test the rest of the system, without noise from the already-reported bug.
>
> This commit therefore adds a torture.printk_shutdown_bug_workaround
> kernel parameter, which causes torture_shutdown() to invoke pr_flush(),
> and print an informative message on the console, immediately before
> invoking kernel_power_off(). When this kernel parameter is not specified,
> it is up to printk() to flush its own buffers.
>
> Suggested-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Reviewed-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
