linux-kernel - Re: [PATCH] mm: trace tlb flush after disabling preemption in try_to_unmap

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Date:	Tue, 21 Jul 2015 14:27:04 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	akpm@...ux-foundation.org, mgorman@...e.de, riel@...hat.com,
	mingo@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: trace tlb flush after disabling preemption in
 try_to_unmap_flush

On Thu 16-07-15 15:35:39, Sasha Levin wrote:
> Commit "mm: send one IPI per CPU to TLB flush all entries after unmapping
> pages" added a trace_tlb_flush() while preemption was still enabled. This
> means that we'll access smp_processor_id() which in turn will get us quite
> a few warnings.
> 
> Fix it by moving the trace to where the preemption is disabled, one line
> down.
> 
> Signed-off-by: Sasha Levin <sasha.levin@...cle.com>

Reviewed-by: Michal Hocko <mhocko@...e.com>

> ---
> 
> The diff is all lies: I've moved trace_tlb_flush() one line down rather
> than get_cpu() a line up ;)
> 
>  mm/rmap.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 30812e9..63ba46c 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -613,9 +613,10 @@ void try_to_unmap_flush(void)
>  	if (!tlb_ubc->flush_required)
>  		return;
>  
> +	cpu = get_cpu();
> +
>  	trace_tlb_flush(TLB_REMOTE_SHOOTDOWN, -1UL);
>  
> -	cpu = get_cpu();
>  	if (cpumask_test_cpu(cpu, &tlb_ubc->cpumask))
>  		percpu_flush_tlb_batch_pages(&tlb_ubc->cpumask);
>  
> -- 
> 1.7.10.4
> 
> --
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-- 
Michal Hocko
SUSE Labs
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