linux-kernel - Re: [PATCH 3/4] time,acct: drop irq save & restore from __acct_update

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Message-ID: <20160201092856.GM6357@twins.programming.kicks-ass.net>
Date:	Mon, 1 Feb 2016 10:28:56 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	riel@...hat.com
Cc:	linux-kernel@...r.kernel.org, fweisbec@...il.com,
	tglx@...utronix.de, mingo@...nel.org, luto@...capital.net,
	clark@...hat.com
Subject: Re: [PATCH 3/4] time,acct: drop irq save & restore from
 __acct_update_integrals

On Sun, Jan 31, 2016 at 09:12:30PM -0500, riel@...hat.com wrote:
>  kernel/tsacct.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/kernel/tsacct.c b/kernel/tsacct.c
> index 9c23584c76c4..31fb6c9746d4 100644
> --- a/kernel/tsacct.c
> +++ b/kernel/tsacct.c
> @@ -124,20 +124,18 @@ static void __acct_update_integrals(struct task_struct *tsk,
>  				    cputime_t utime, cputime_t stime)
>  {
>  	cputime_t time, dtime;
> -	unsigned long flags;
>  	u64 delta;
>  
>  	if (!likely(tsk->mm))
>  		return;
>  
> -	local_irq_save(flags);
>  	time = stime + utime;
>  	dtime = time - tsk->acct_timexpd;
>  	/* Avoid division: cputime_t is often in nanoseconds already. */
>  	delta = cputime_to_nsecs(dtime);
>  
>  	if (delta < TICK_NSEC)
> -		goto out;
> +		return;
>  
>  	tsk->acct_timexpd = time;
>  	/*
> @@ -147,8 +145,6 @@ static void __acct_update_integrals(struct task_struct *tsk,
>  	 */
>  	tsk->acct_rss_mem1 += delta * get_mm_rss(tsk->mm) >> 10;
>  	tsk->acct_vm_mem1 += delta * tsk->mm->total_vm >> 10;
> -out:
> -	local_irq_restore(flags);
>  }

Like Frederic said on your last posting, at the very least
do_exit()->acct_update_integrals() will not have IRQs disabled.

Its just the acct_account_cputime() callers that I suspect will all have
IRQs disabled, but it would still be goot to verify that with a
WARN_ON(!irqs_disabled()) test in there for at least one test run, and
then include that you did this in the Changelog.