Re: RCU callback and scheduling while atomic!

[Herbert Poetzl <herbert@13thfloor.at>]

On Tue, Aug 31, 2004 at 09:51:40PM +0530, Dipankar Sarma wrote:
> On Tue, Aug 31, 2004 at 06:17:10PM +0200, Herbert Poetzl wrote:
> > 
> > it seems that the RCU callback is not allowed 
> > to (re-)schedule, as it is done occasionally by 
> > put_namespace() for example, as I keep getting 
> > "bad: scheduling while atomic!", when I do so ...
> > 
> > now the question: what is the 'correct' way to
> > drop a reference to a namespace when freeing up 
> > a structure from an RCU callback?
> 
> You are right about not allowing schedule from callbacks. The callbacks
> are called from softirq context.
> 
> Without your current code, it is difficult to say how to do this but here are
> some guesses - 
> 
> 1. You could mark the freed up structure deleted on update, do
>    put_namspace() and do only the freeing in the rcu callback.
>    dentries do this.
> 
> 2. If not performance critical, you could use a workqueue to
>    do the actual freeing including put_namespace(). Just wake up
>    from the rcu callback.

ah, okay, I see, although it isn't time critical,
it seems to me that the first is the best choice
in my case, thanks for the hints ...

> These may or may not be applicable to your case. More details will
> help.

thanks,
Herbert

> Thanks
> Dipankar
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