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Date:   Wed, 23 Sep 2020 09:42:51 -0400
From:   Rafael Aquini <aquini@redhat.com>
To:     Andrew Morton <akpm@linux-foundation.org>
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: <20200923134251.GN795820@optiplex-lnx>
References: <20200922184838.978540-1-aquini@redhat.com>
 <20200922124750.67a20d9764ec098b17705407@linux-foundation.org>
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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?