linux-kernel - Re: [PATCH v4 01/27] lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions

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Date:   Fri, 21 Feb 2020 10:08:55 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        mingo@...nel.org, joel@...lfernandes.org,
        gregkh@...uxfoundation.org, gustavo@...eddedor.com,
        tglx@...utronix.de, paulmck@...nel.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        luto@...nel.org, tony.luck@...el.com, frederic@...nel.org,
        dan.carpenter@...cle.com, mhiramat@...nel.org
Subject: Re: [PATCH v4 01/27] lockdep: Teach lockdep about "USED" <-
 "IN-NMI" inversions

On Fri, 21 Feb 2020 14:34:17 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -379,13 +379,13 @@ void lockdep_init_task(struct task_struc
>  
>  void lockdep_off(void)
>  {
> -	current->lockdep_recursion++;
> +	current->lockdep_recursion += BIT(16);
>  }
>  EXPORT_SYMBOL(lockdep_off);
>  
>  void lockdep_on(void)
>  {
> -	current->lockdep_recursion--;
> +	current->lockdep_recursion -= BIT(16);
>  }
>  EXPORT_SYMBOL(lockdep_on);
>  

> +
> +static bool lockdep_nmi(void)
> +{
> +	if (current->lockdep_recursion & 0xFFFF)

Nitpick, but the association with bit 16 and this mask really should be
defined as a macro somewhere and not have hard coded numbers.

-- Steve

> +		return false;
> +
> +	if (!in_nmi())
> +		return false;
> +
> +	return true;
> +}
> +