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Date: Thu, 7 Sep 2017 13:39:09 -0700
From: Tejun Heo <tj@kernel.org>
To: Eric Biggers <ebiggers3@gmail.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Chris Wilson <chris@chris-wilson.co.uk>,
        Dmitry Vyukov <dvyukov@google.com>,
        Matthew Wilcox <mawilcox@microsoft.com>,
        dri-devel@lists.freedesktop.org, stable@vger.kernel.org
Subject: Re: [PATCH] idr: remove WARN_ON_ONCE() when trying to replace
 negative ID
Message-ID: <20170907203909.GV1774378@devbig577.frc2.facebook.com>
References: <20170906235306.20534-1-ebiggers3@gmail.com>
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On Wed, Sep 06, 2017 at 04:53:06PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> IDR only supports non-negative IDs.  There used to be a
> 'WARN_ON_ONCE(id < 0)' in idr_replace(), but it was intentionally
> removed by commit 2e1c9b286765 ("idr: remove WARN_ON_ONCE() on negative
> IDs").  Then it was added back by commit 0a835c4f090a ("Reimplement IDR
> and IDA using the radix tree").  However it seems that adding it back
> was a mistake, given that some users such as drm_gem_handle_delete()
> (DRM_IOCTL_GEM_CLOSE) pass in a value from userspace to idr_replace(),
> allowing the WARN_ON_ONCE to be triggered.  drm_gem_handle_delete()
> actually just wants idr_replace() to return an error code if the ID is
> not allocated, including in the case where the ID is invalid (negative).

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun