linux-kernel - Re: [patch v11 09/13] task isolation: add preempt notifier to sync per-CPU vmstat dirty info to thread info

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Date:   Mon, 7 Feb 2022 16:36:07 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Marcelo Tosatti <mtosatti@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Nitesh Lal <nilal@...hat.com>,
        Nicolas Saenz Julienne <nsaenzju@...hat.com>,
        Christoph Lameter <cl@...ux.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alex Belits <abelits@...its.com>, Peter Xu <peterx@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Oscar Shiang <oscar0225@...email.tw>
Subject: Re: [patch v11 09/13] task isolation: add preempt notifier to sync
 per-CPU vmstat dirty info to thread info

On Fri, Feb 04, 2022 at 02:35:46PM -0300, Marcelo Tosatti wrote:
> If a thread has task isolation activated, is preempted by thread B,
> which marks vmstat information dirty, and is preempted back in,
> one might return to userspace with vmstat dirty information on the 
> CPU in question.
> 
> To address this problem, add a preempt notifier that transfers vmstat dirty
> information to TIF_TASK_ISOL thread flag.

Ah ok that answers my previous question :)

> Index: linux-2.6/mm/vmstat.c
> ===================================================================
> --- linux-2.6.orig/mm/vmstat.c
> +++ linux-2.6/mm/vmstat.c
> @@ -353,6 +353,13 @@ void init_sync_vmstat(void)
>  	set_thread_flag(TIF_TASK_ISOL);
>  }
>  EXPORT_SYMBOL_GPL(vmstat_dirty);
> +
> +void vmstat_dirty_to_thread_flag(void)
> +{
> +	if (raw_cpu_read(vmstat_dirty) == true)

__this_cpu_read()?

> +		set_thread_flag(TIF_TASK_ISOL);
> +}
> +EXPORT_SYMBOL_GPL(vmstat_dirty_to_thread_flag);
>  #else
>  static inline void mark_vmstat_dirty(void)
>  {
> 
>