linux-kernel - Re: sys_sched_yield keeps locked irq before call of schedule()

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Message-ID: <20081105130113.GB29548@elte.hu>
Date:	Wed, 5 Nov 2008 14:01:13 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Zdenek Kabelac <zdenek.kabelac@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: sys_sched_yield keeps locked irq before call of schedule()


* Zdenek Kabelac <zdenek.kabelac@...il.com> wrote:

> Hi
> 
> With recent 2.6.28-rc3 kernel I've noticed that schedule() is 
> sometime being called with locked IRQ
> 
> Call Trace:
>  [<ffffffff81334592>] _spin_lock_irq+0x92/0xa0
>  [<ffffffff8133126b>] schedule+0x13b/0x4cb
>  [<ffffffff81013c10>] ? native_sched_clock+0x70/0xa0
>  [<ffffffff81040930>] ? sys_sched_yield+0x0/0x80
>  [<ffffffff810409a5>] sys_sched_yield+0x75/0x80
>  [<ffffffff8100c6bb>] system_call_fastpath+0x16/0x1b

is this some special warning you added? The stock kernel certainly 
does not emit this warning.

> Which is a result of the function sys_sched_yield() that calls 
> schedule() while it keeps irq.
> 
> Is it correct to call the function schedule() which 'usually' 
> expects irq being unlocked and do some 'lenghty' operations (i.e. 
> debug statistics) which do not need to keep irq locked for such a 
> long time?

the debug statistics are all fast and we disable interrupts straight 
away when entering the schedule().

	Ingo
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