[uml-devel] Re: "Sleeping in atomic section" with ubd aio patch

[Jeff Dike <jdike@addtoit.com>]

On Tue, Sep 13, 2005 at 08:01:40PM +0200, Blaisorblade wrote:
> It's just because things are called under spinlocks and GFP_KERNEL is used - 
> but if possible, it'd be better to use something better than GFP_ATOMIC 
> (since this is performance critical).

This would be ubd_io_lock, which is taken for us by the block layer before 
entering do_ubd_request.  We could make that a GFP_ATOMIC allocation, except
that we have already dequeued the request, so would need to do
something with it if the allocation failed.

I'm wondering if we can drop the lock before do_io and pick it up
afterwards.  The bitmap argument is a global, which is a problem.  Two
racing requests could result in one writing out a bitmap which is
either too old or too new.

So, I'm not sure how to handle this.  We could requeue what's left of
the request if an allocation failure happens.  We could drop the lock
and pick it up later, but we have to be careful to write out the
current bitmap, not one which we saved earlier or one which has been
updated to reflect a racing request which is coming through later.

				Jeff




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