Re: inappropriate use of in_atomic()

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Date:	Tue, 31 May 2005 02:20:27 +0200
To: Andrew Morton <akpm@osdl.org>

On Thu, Mar 10, 2005 at 08:40:06PM -0800, Andrew Morton wrote:
>
> in_atomic() is not a reliable indication of whether it is currently safe
> to call schedule().
>
> This is because the lockdepth beancounting which in_atomic() uses is only
> accumulated if CONFIG_PREEMPT=y. in_atomic() will return false inside
> spinlocks if CONFIG_PREEMPT=n.
>
> Consequently the use of in_atomic() in the below files is probably
> deadlocky if CONFIG_PREEMPT=n:

I haven't looked deeper into it, but as a FYI the following files from
your list still use in_atomic in 2.6.12-rc5-mm1:

>...
> drivers/net/irda/sir_kthread.c
> drivers/net/wireless/airo.c
> drivers/video/amba-clcd.c
> drivers/acpi/osl.c
> drivers/ieee1394/ieee1394_transactions.c
>...

> Note that the same beancounting is used for the "scheduling while atomic"
> warning, so if the code calls schedule with locks held, we won't get a
> warning. Both are tied to CONFIG_PREEMPT=y.
>
> The kernel provides no reliable runtime way of detecting whether or not it
> is safe to call schedule().
>
> Can we please find ways to change the above code to not use in_atomic()?
> Then we can whack #ifndef MODULE around its definition to reduce
> reoccurrences. Will probably rename it to something more scary as well.
>
> Thanks.

cu
Adrian

-- 
       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed
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• Previous message: Adrian Bunk: "[2.6 patch] Kconfig: rename "---help---" to "help" in Kconfig files (first part) (fwd)"
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