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

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Date:	Wed, 5 Nov 2008 14:09:36 +0100
From:	"Zdenek Kabelac" <zdenek.kabelac@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
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()

2008/11/5 Ingo Molnar <mingo@...e.hu>:
>
> * 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.

Yes - it's my personal debug checker that tries to watch wether irq &
irqsafe are running in pair.
So it shows a warning if there is a call of spin_lock_irq and irq is
already dissabled.

>
>> 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().

IRQ is disabled with spin_lock_irc() inside schedule() and it looks
like there is quite a few lines above which receive 'extra' bonus with
being run without enabled irq, but as I said - I'm just checking
whether this is intentional or not.

Zdenek
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