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Date:   Thu, 24 Sep 2020 19:59:14 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Rafael Aquini <aquini@redhat.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        ying.huang@intel.com
Subject: Re: [PATCH] mm: swapfile: avoid split_swap_cluster() NULL pointer
 dereference
Message-Id: <20200924195914.d240877a10e22b457bd9b45d@linux-foundation.org>
In-Reply-To: <20200923134251.GN795820@optiplex-lnx>
References: <20200922184838.978540-1-aquini@redhat.com>
        <20200922124750.67a20d9764ec098b17705407@linux-foundation.org>
        <20200923134251.GN795820@optiplex-lnx>
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On Wed, 23 Sep 2020 09:42:51 -0400 Rafael Aquini <aquini@redhat.com> wrote:

> On Tue, Sep 22, 2020 at 12:47:50PM -0700, Andrew Morton wrote:
> > On Tue, 22 Sep 2020 14:48:38 -0400 Rafael Aquini <aquini@redhat.com> wrote:
> > 
> > > The swap area descriptor only gets struct swap_cluster_info *cluster_info
> > > allocated if the swapfile is backed by non-rotational storage.
> > > When the swap area is laid on top of ordinary disk spindles, lock_cluster()
> > > will naturally return NULL.
> > > 
> > > CONFIG_THP_SWAP exposes cluster_info infrastructure to a broader number of
> > > use cases, and split_swap_cluster(), which is the counterpart of split_huge_page()
> > > for the THPs in the swapcache, misses checking the return of lock_cluster before
> > > operating on the cluster_info pointer.
> > > 
> > > This patch addresses that issue by adding a proper check for the pointer
> > > not being NULL in the wrappers cluster_{is,clear}_huge(), in order to avoid
> > > crashes similar to the one below:
> > > 
> > > ...
> > >
> > > Fixes: 59807685a7e77 ("mm, THP, swap: support splitting THP for THP swap out")
> > > Signed-off-by: Rafael Aquini <aquini@redhat.com>
> > 
> > Did you consider cc:stable?
> >
> 
> UGH! I missed adding it to my cc list. Shall I just forward it, now, or
> do you prefer a fresh repost?

I added the cc:stable to my copy.