linux-kernel - Re: [PATCH 40/45] powerpc, irq: Use GFP_ATOMIC allocations in atomic context

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Message-ID: <20130625020842.GD14051@concordia>
Date:	Tue, 25 Jun 2013 12:08:42 +1000
From:	Michael Ellerman <michael@...erman.id.au>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	tglx@...utronix.de, peterz@...radead.org, tj@...nel.org,
	oleg@...hat.com, paulmck@...ux.vnet.ibm.com, rusty@...tcorp.com.au,
	mingo@...nel.org, akpm@...ux-foundation.org, namhyung@...nel.org,
	walken@...gle.com, vincent.guittot@...aro.org,
	laijs@...fujitsu.com, rostedt@...dmis.org,
	wangyun@...ux.vnet.ibm.com, xiaoguangrong@...ux.vnet.ibm.com,
	sbw@....edu, fweisbec@...il.com, zhong@...ux.vnet.ibm.com,
	nikunj@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-arch@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Ian Munsie <imunsie@....ibm.com>
Subject: Re: [PATCH 40/45] powerpc, irq: Use GFP_ATOMIC allocations in atomic
 context

On Sun, Jun 23, 2013 at 07:17:00PM +0530, Srivatsa S. Bhat wrote:
> The function migrate_irqs() is called with interrupts disabled
> and hence its not safe to do GFP_KERNEL allocations inside it,
> because they can sleep. So change the gfp mask to GFP_ATOMIC.

OK so it gets there via:
  __stop_machine()
    take_cpu_down()
      __cpu_disable()
        smp_ops->cpu_disable()
          generic_cpu_disable()
            migrate_irqs()

> diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
> index ea185e0..ca39bac 100644
> --- a/arch/powerpc/kernel/irq.c
> +++ b/arch/powerpc/kernel/irq.c
> @@ -412,7 +412,7 @@ void migrate_irqs(void)
>  	cpumask_var_t mask;
>  	const struct cpumask *map = cpu_online_mask;
>  
> -	alloc_cpumask_var(&mask, GFP_KERNEL);
> +	alloc_cpumask_var(&mask, GFP_ATOMIC);

We're not checking for allocation failure, which we should be.

But this code is only used on powermac and 85xx, so it should probably
just be a TODO to fix this up to handle the failure.

cheers
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