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From:   Willem de Bruijn <willemb@google.com>
Date:   Thu, 7 Jan 2021 16:07:54 -0500
Message-ID: <CA+FuTSdsTFHY5Yx8y5UHGYqsz=FGevjYn_Kzy-p3kwx-vUxdDw@mail.gmail.com>
Subject: Re: [BUG] from x86: Support kmap_local() forced debugging
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Jakub Kicinski <kuba@kernel.org>,
        David Miller <davem@davemloft.net>,
        Jonathan Lemon <jonathan.lemon@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Matthew Wilcox <willy@infradead.org>,
        Daniel Vetter <daniel@ffwll.ch>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Netdev <netdev@vger.kernel.org>
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On Thu, Jan 7, 2021 at 3:53 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Thu, 7 Jan 2021 11:47:02 -0800
> Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
> > On Wed, Jan 6, 2021 at 8:45 PM Willem de Bruijn <willemb@google.com> wrote:
> > >
> > > But there are three other kmap_atomic callers under net/ that do not
> > > loop at all, so assume non-compound pages. In esp_output_head,
> > > esp6_output_head and skb_seq_read. The first two directly use
> > > skb_page_frag_refill, which can allocate compound (but not
> > > __GFP_HIGHMEM) pages, and the third can be inserted with
> > > netfilter xt_string in the path of tcp transmit skbs, which can also
> > > have compound pages. I think that these could similarly access
> > > data beyond the end of the kmap_atomic mapped page. I'll take
> > > a closer look.
> >
> > Thanks.
> >
> > Note that I have flushed my random one-liner patch from my system, and
> > expect to get a proper fix through the normal networking pulls.
> >
> > And _if_ the networking people feel that my one-liner was the proper
> > fix, you can use it and add my sign-off if you want to, but it really
> > was more of a "this is the quick ugly fix for testing" rather than
> > anything else.

I do think it is the proper fix as is. If no one else has comments, I
can submit it through the net tree.

It won't address the other issues that became apparent only as a
result of this. I'm preparing separate patches for those.

> Please add:
>
>   Link: https://lore.kernel.org/linux-mm/20210106180132.41dc249d@gandalf.local.home/
>   Reported-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
>
> And if you take Linus's patch, please add my:
>
>   Tested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
>
> and if you come up with another patch, please send it to me for testing.
>
> Thanks!

Will do, thanks.