linux-kernel - Re: [PATCH -mm 4/4] irq_work, Use llist in irq

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Message-ID: <20110906105750.GD21602@Krystal>
Date:	Tue, 6 Sep 2011 06:57:50 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Huang Ying <ying.huang@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH -mm 4/4] irq_work, Use llist in irq_work

* Huang Ying (ying.huang@...el.com) wrote:
> Use llist in irq_work instead of the lock-less linked list
> implementation in irq_work to avoid the code duplication.
> 
> Signed-off-by: Huang Ying <ying.huang@...el.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> ---
>  include/linux/irq_work.h |   15 ++++---
>  kernel/irq_work.c        |   92 ++++++++++++++++-------------------------------
>  2 files changed, 41 insertions(+), 66 deletions(-)
> 
[...]
> -static void __irq_work_queue(struct irq_work *entry)
> +static void __irq_work_queue(struct irq_work *work)
>  {
> -	struct irq_work *next;
> -
>  	preempt_disable();
>  
> -	do {
> -		next = __this_cpu_read(irq_work_list);
> -		/* Can assign non-atomic because we keep the flags set. */
> -		entry->next = next_flags(next, IRQ_WORK_FLAGS);
> -	} while (this_cpu_cmpxchg(irq_work_list, next, entry) != next);
> -
> +	llist_add(&work->llnode, &__get_cpu_var(irq_work_list));
>  	/* The list was empty, raise self-interrupt to start processing. */
> -	if (!irq_work_next(entry))
> +	if (!work->llnode.next)


Hrm. What happens if this function gets delayed between llist_add and
"if (!work->llnode.next)" ? It seems like the threads performing
llist_del_all would be within its right to free the memory pointed to by
work in the meantime.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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