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Date:   Fri, 8 Jul 2022 01:24:47 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     dsterba@suse.cz, fdmanana@kernel.org, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 0/3] btrfs: fix a couple sleeps while holding a spinlock
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References: <cover.1657097693.git.fdmanana@suse.com>
 <20220707163144.GG15169@twin.jikos.cz>
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On Thu, Jul 07, 2022 at 06:31:44PM +0200, David Sterba wrote:
> Adding Matthew to CC
> 
> On Wed, Jul 06, 2022 at 10:09:44AM +0100, fdmanana@kernel.org wrote:
> > From: Filipe Manana <fdmanana@suse.com>
> > 
> > After the recent conversions of a couple radix trees to XArrays, we now
> > can end up attempting to sleep while holding a spinlock.
> 
> Ouch, I worked on the asumption that the old preload API is
> transparently provided by xarray and that sleeping under spinlock won't
> happen, otherwise the conversion from radix to xarray is not just an API
> rename. Note that for some time the radix_tree structure was just an
> alias for xarray, so this is not a new behaviour.

Umm ... the *structure* is identical, but the *API* is not.  Or the
conversion would have happened long ago.  There is no preload API
for the XArray because it's one of the worst features of the radix
tree API.