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Date:   Tue, 2 Apr 2019 04:26:56 -0700
From:   Matthew Wilcox <willy@infradead.org>
To:     Qiang Yu <yuq825@gmail.com>
Cc:     Stephen Rothwell <sfr@canb.auug.org.au>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Intel Graphics <intel-gfx@lists.freedesktop.org>,
        DRI <dri-devel@lists.freedesktop.org>,
        Linux Next Mailing List <linux-next@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Eric Anholt <eric@anholt.net>
Subject: Re: linux-next: build failure after merge of the drm-misc tree
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On Tue, Apr 02, 2019 at 01:55:03PM +0800, Qiang Yu wrote:
> Thanks, patch is:
> Reviewed-by: Qiang Yu <yuq825@gmail.com>

This looks like a fairly naive conversion from the old IDR API to the
XArray API.  You should be able to remove mgr->lock entirely, relying on
the xa_lock for synchronising free and get.  If you think it's worth it,
you could even use kfree_rcu() to free the ctx and kref_get_unless_zero()
and then your get path would be lock-free.