linux-kernel - Re: [PATCH 1/5] vfork: don't freezer_count() for in-kernel users of CLONE

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Message-ID: <20130216170545.GB4910@redhat.com>
Date:	Sat, 16 Feb 2013 18:05:45 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Mandeep Singh Baines <msb@...omium.org>
Cc:	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH 1/5] vfork: don't freezer_count() for in-kernel users
	of CLONE_VFORK

On 02/16, Mandeep Singh Baines wrote:
>
> We don't need to call freezer_do_not_count() for in-kernel users
> of CLONE_VFORK since exec will get called in bounded time.
>
> We don't want to call freezer_count() for in-kernel users because
> they may be holding locks. freezer_count() calls try_to_freeze().
> We don't want to freeze an in-kernel user because it may be
> holding locks.

I can only repeat my question ;)

	Who? We should not do this anyway. And __call_usermodehelper() doesn't
	afaics.

	OK, its caller (process_one_work) does lock_map_acquire() for debugging
	purposes, this can "confuse" print_held_locks_bug(). But this thread is
	PF_NOFREEZE ?

Previously this was needed to suppress the false positive. Now that 2/5
checks PF_NOFREEZE, why do we need this change?

> @@ -722,9 +722,11 @@ static int wait_for_vfork_done(struct task_struct *child,
>  {
>  	int killed;
>
> -	freezer_do_not_count();
> +	if (!(current->flags & PF_KTHREAD))
> +		freezer_do_not_count();

If I missed something and we really need this, imho this needs a comment.

Oleg.

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