Re: [PATCH] Register atomic_notifiers in atomic context

[Andrew Morton <akpm@osdl.org>]

Alan Stern <stern@rowland.harvard.edu> wrote:
>
>  The calls to register_cpu_notifier are harder.  That chain really does 
>  need to be blocking

Why?

> which means we can't avoid calling down_write.  The 
>  only solution I can think of is to use down_write_trylock in the 
>  blocking_notifier_chain_register and unregister routines, even though 
>  doing that is a crock.
> 
>  Or else change __down_read and __down_write to use spin_lock_irqsave 
>  instead of spin_lock_irq.  What do you think would be best?

Nothing's pretty.  Perhaps look at system_state and not do any locking at all
in early boot?

>  > I'd suggest that in further development, you enable might_sleep() in early
>  > boot - that would have caught such things..
> 
>  Not a bad idea.  I presume that removing the "system_state == 
>  SYSTEM_RUNNING" test in __might_sleep will have that effect?

Yup.
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