linux-kernel - Re: [tip:x86/urgent] x86-32: Restore irq stacks NUMA-aware allocations

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Date:	Fri, 29 Oct 2010 22:53:07 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
	hpa@...or.com, linux-kernel@...r.kernel.org, brgerst@...il.com,
	tglx@...utronix.de, mingo@...e.hu,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/urgent] x86-32: Restore irq stacks NUMA-aware
 allocations

Le samedi 30 octobre 2010 à 00:28 +0400, Cyrill Gorcunov a écrit :
> On Fri, Oct 29, 2010 at 08:32:26PM +0200, Peter Zijlstra wrote:
> > On Fri, 2010-10-29 at 06:43 +0000, tip-bot for Eric Dumazet wrote:
> > > +       irqctx = page_address(alloc_pages_node(cpu_to_node(cpu),
> > > +                                              THREAD_FLAGS,
> > > +                                              THREAD_ORDER)); 
> > 
> > Shouldn't we be checking for a NULL return from alloc_pages_node()
> > before calling page_address() on it?
> > --
> 

I didnt check for NULL because original code was not either.

If you cannot allocate memory for the IRQ stack, only choice is to crash
anyway.

Adding BUG_ON() is not that helpful in this respect.

>  Something like below I guess, but probably we could try to allocate
> on appropriate NUMA node first and if it fails -- via old alloc_pages
> and if it fail in turn -- then we panic.
> 
>   Cyrill
> ---
>  arch/x86/kernel/irq_32.c |   17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> Index: linux-2.6.git/arch/x86/kernel/irq_32.c
> =====================================================================
> --- linux-2.6.git.orig/arch/x86/kernel/irq_32.c
> +++ linux-2.6.git/arch/x86/kernel/irq_32.c
> @@ -122,13 +122,16 @@ execute_on_irq_stack(int overflow, struc
>  void __cpuinit irq_ctx_init(int cpu)
>  {
>  	union irq_ctx *irqctx;
> +	struct page *page;
>  
>  	if (per_cpu(hardirq_ctx, cpu))
>  		return;
>  
> -	irqctx = page_address(alloc_pages_node(cpu_to_node(cpu),
> -					       THREAD_FLAGS,
> -					       THREAD_ORDER));
> +	page = alloc_pages_node(cpu_to_node(cpu),
> +				THREAD_FLAGS, THREAD_ORDER);
> +	BUG_ON(!page);
> +
> +	irqctx				= page_address(page);
>  	irqctx->tinfo.task		= NULL;
>  	irqctx->tinfo.exec_domain	= NULL;
>  	irqctx->tinfo.cpu		= cpu;
> @@ -137,9 +140,11 @@ void __cpuinit irq_ctx_init(int cpu)
>  
>  	per_cpu(hardirq_ctx, cpu) = irqctx;
>  
> -	irqctx = page_address(alloc_pages_node(cpu_to_node(cpu),
> -					       THREAD_FLAGS,
> -					       THREAD_ORDER));
> +	page = alloc_pages_node(cpu_to_node(cpu),
> +				THREAD_FLAGS, THREAD_ORDER);
> +	BUG_ON(!page);
> +
> +	irqctx				= page_address(page);
>  	irqctx->tinfo.task		= NULL;
>  	irqctx->tinfo.exec_domain	= NULL;
>  	irqctx->tinfo.cpu		= cpu;


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