linux-kernel - xarray reserve/release?

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Date:   Tue, 19 Feb 2019 16:53:49 -0700
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org
Subject: xarray reserve/release?

Hey Matt,

Did you intend that xa_release doesn't work on allocating arrays:

	xa_init_flags(&xa, XA_FLAGS_ALLOC);
	xa_reserve(&xa, 0, GFP_KERNEL);
	WARN_ON(xa_empty(&xa));
	xa_release(&xa, 0);
	WARN_ON(!xa_empty(&xa));

Triggers the second WARN_ON. 

If FLAGS_ALLOC is removed this passes

This creates kind of a confusing / super unexpected situation where 

   xa_for_each (xa, id)
       xa_erase(xa, id);
   WARN_ON(!xa_empty(&xa))

Is not safe with XA_FLAGS_ALLOC??

Seems like at least deserves a documentation note.. Or maybe ALLOC
xa_empty should do something different?

Thanks,
Jason