Re: [PATCH v13] vhost: Reintroduces support of kthread API and adds mode selection

[Simon Horman <horms@kernel.org>]

On Tue, Jul 15, 2025 at 08:43:45PM +0200, Markus Elfring wrote:
> > This patch reintroduces kthread mode for vhost workers and provides
> > configuration to select between kthread and task worker.
> …
> 
> Is there a need to reconsider the relevance once more for the presented
> cover letter?
> 
> 
> …
> > +++ b/drivers/vhost/vhost.c
> …
> > +static int vhost_attach_task_to_cgroups(struct vhost_worker *worker)
> > +{
> …
> > +	vhost_worker_queue(worker, &attach.work);
> > +
> > +	mutex_lock(&worker->mutex);
> …
> > +	worker->attachment_cnt = saved_cnt;
> > +
> > +	mutex_unlock(&worker->mutex);
> …
> 
> Under which circumstances would you become interested to apply a statement
> like “guard(mutex)(&worker->mutex);”?
> https://elixir.bootlin.com/linux/v6.16-rc6/source/include/linux/mutex.h#L225

Quoting the documentation, I'd suggest these circumstances:

  1.6.5. Using device-managed and cleanup.h constructs

  Netdev remains skeptical about promises of all “auto-cleanup” APIs,
  including even devm_ helpers, historically. They are not the preferred
  style of implementation, merely an acceptable one.

  Use of guard() is discouraged within any function longer than 20 lines,
  scoped_guard() is considered more readable. Using normal lock/unlock is
  still (weakly) preferred.

  Low level cleanup constructs (such as __free()) can be used when building
  APIs and helpers, especially scoped iterators. However, direct use of
  __free() within networking core and drivers is discouraged. Similar
  guidance applies to declaring variables mid-function.

https://docs.kernel.org/6.16-rc6/process/maintainer-netdev.html#using-device-managed-and-cleanup-h-constructs

IOW, the code is fine as-is.