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

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Date:	Thu, 10 Dec 2009 11:09:08 +0100
From:	Pavel Machek <pavel@....cz>
To:	Xiaotian Feng <dfeng@...hat.com>
Cc:	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

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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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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