linux-kernel - Re: [PATCH 2/6] irq_work: Implement remote queueing

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Date:	Wed, 25 Jun 2014 12:07:05 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Stephen Warren <swarren@...dotorg.org>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Kevin Hilman <khilman@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>
Subject: Re: [PATCH 2/6] irq_work: Implement remote queueing

On 06/25/2014 10:47 AM, Peter Zijlstra wrote:
> On Wed, Jun 25, 2014 at 07:12:34AM +0200, Peter Zijlstra wrote:
>> On Tue, Jun 24, 2014 at 02:33:41PM -0600, Stephen Warren wrote:
>>> On 06/10/2014 09:15 AM, Frederic Weisbecker wrote:
>>>> irq work currently only supports local callbacks. However its code
>>>> is mostly ready to run remote callbacks and we have some potential user.

[...]

>> Right you are.. I think I'll just remove the BUG_ON(), Frederic?
> 
> Something a little so like:
> 
> ---
> Subject: irq_work: Remove BUG_ON in irq_work_run_list()

I think this should be irq_work_run(), see below...

> From: Peter Zijlstra <peterz@...radead.org>
> Date: Wed Jun 25 07:13:07 CEST 2014
> 
> Because of a collision with 8d056c48e486 ("CPU hotplug, smp: flush any
> pending IPI callbacks before CPU offline"), which ends up calling
> hotplug_cfd()->flush_smp_call_function_queue()->run_irq_work(), which


s/run_irq_work/irq_work_run


> is not from IRQ context.
> 
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Reported-by: Stephen Warren <swarren@...dotorg.org>
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> ---
>  kernel/irq_work.c |    2 --
>  1 file changed, 2 deletions(-)
> 
> --- a/kernel/irq_work.c
> +++ b/kernel/irq_work.c
> @@ -130,8 +130,6 @@ static void irq_work_run_list(struct lli
>  	struct irq_work *work;
>  	struct llist_node *llnode;
>  
> -	BUG_ON(!irqs_disabled());
> -

I don't think irqs_disabled() is the problematic condition, since
hotplug_cfg() invokes irq_work_run() from CPU_DYING context (which has
irqs disabled). I guess you meant to remove the in_irq() check inside
irq_work_run() instead?

Regards,
Srivatsa S. Bhat

>  	if (llist_empty(list))
>  		return;
>  
> 

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