On Tue, Jun 21, 2022 at 10:58:27PM +0206, John Ogness wrote:
> 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.
Fair points!
The main value to me is to avoid me having to pile through code to relearn
the incantation pr_flush(1000, true). Which, now that you mention it,
could be dealt with by adding a comment:
// pr_flush(1000, true); // If needed to flush printk() buffers.
This definitely will not go into the upcoming merge window, so there is
plenty of time to give it some thought.
> > 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>
Thank you!
Thanx, Paul
