linux-kernel - Re: [PATCH] ACPICA: don't cond_resched() when irq_disabled or in

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Date:	Thu, 10 Dec 2009 20:58:45 +0300
From:	Alexey Starikovskiy <aystarik@...il.com>
To:	Pavel Machek <pavel@....cz>
CC:	Xiaotian Feng <dfeng@...hat.com>, lenb@...nel.org,
	ming.m.lin@...el.com, robert.moore@...el.com,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ACPICA: don't cond_resched() when irq_disabled or in_atomic

Hi Pavel,

Please elaborate... Your comments "ugly as hell" are too often to be
specific...
There is only one use of ACPI_PREEMPTION_POINT(), and it is in the
ACPICA code,
which we all agreed to keep OS independent, thus the need for #define.
Do you see any other way to add preemption point without introducing
Linux-specific
code into ACPICA?

Thanks,
Alex.


Pavel Machek пишет:
> On Fri 2009-12-04 12:26:00, Xiaotian Feng wrote:
>   
>> commit 8bd108d adds preemption point after each opcode parse, then
>> a sleeping function called from invalid context bug was founded
>> during suspend/resume stage. this was fixed in commit abe1dfa by
>> don't cond_resched when irq_disabled. But recent commit 138d156 changes
>> the behaviour to don't cond_resched when in_atomic. This makes the
>> sleeping function called from invalid context bug happen again, which
>> is reported in http://lkml.org/lkml/2009/12/1/371.
>>
>> The fix is to cond_sched() only when preemptible, which means not in
>> irq_disabled or in_atomic.
>>
>> @@ -152,7 +152,7 @@ static inline void *acpi_os_acquire_object(acpi_cache_t * cache)
>>  #include <linux/hardirq.h>
>>  #define ACPI_PREEMPTION_POINT() \
>>  	do { \
>> -		if (!in_atomic_preempt_off()) \
>> +		if (preemptible()) \
>>  			cond_resched(); \
>>  	} while (0)
>>     
>
> Note that this is ugly as hell. It means we have two acpi
> interpretters in kernel, one for preemptible, one for non-preemptible,
> with very different behaviour.
>
> It would be slightly nicer to pass the "preemptible" info explicitely,
> as function parameters.
>
> It would be even better not to need that difference.
>
> 									Pavel
>   

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