linux-kernel - Re: [PATCH 3/3] irq: Comment on the use of inline stack for ksoftirq

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Message-ID: <20130905225649.GE20519@somewhere>
Date:	Fri, 6 Sep 2013 00:56:50 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@....ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	James Hogan <james.hogan@...tec.com>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Helge Deller <deller@....de>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 3/3] irq: Comment on the use of inline stack for ksoftirq

On Thu, Sep 05, 2013 at 05:33:24PM +0200, Frederic Weisbecker wrote:
> Ksoftirqd shouldn't need softirq stack since it's executing
> in a kernel thread with a callstack that is only beginning at
> this stage.
> 
> Lets comment about that for clarity.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@....ibm.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Paul Mackerras <paulus@....ibm.com>
> Cc: James Hogan <james.hogan@...tec.com>
> Cc: James E.J. Bottomley <jejb@...isc-linux.org>
> Cc: Helge Deller <deller@....de>
> Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
> Cc: Heiko Carstens <heiko.carstens@...ibm.com>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ---
>  kernel/softirq.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index 657e047..1de0322 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -759,6 +759,7 @@ static void run_ksoftirqd(unsigned int cpu)
>  {
>  	local_irq_disable();
>  	if (local_softirq_pending()) {
> +		/* No need to use softirq stack here */

Looking at that comment now, it probably deserve more details :)

>  		__do_softirq();
>  		rcu_note_context_switch(cpu);
>  		local_irq_enable();
> -- 
> 1.7.5.4
> 
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