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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 11 Jun 2018 11:44:05 -0700
Message-ID: <CA+55aFz4uBHaWnBarVUEG90s2ucyVtoLmwYpYVwDV+XQESNRqw@mail.gmail.com>
Subject: Re: [PULL] vhost: cleanups and fixes
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     KVM list <kvm@vger.kernel.org>,
        virtualization <virtualization@lists.linux-foundation.org>,
        Network Development <netdev@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        wei.w.wang@intel.com
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On Mon, Jun 11, 2018 at 11:32 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> So now we apparently do a GFP_KERNEL allocation insider the mm zone
> lock, which is broken on just _so_ many levels.

Oh, I see the comment about how it doesn't actually do an allocation
at all because it's a single-entry.

Still too damn ugly to live, and much too fragile. No way in hell do
we even _hint_ at a GFP_KERNEL when we're inside a context that can't
do any memory allocation at all.

Plus I'm not convinced it's a "no allocation" path even despite that
comment, because it also does a "dma_map_page()" etc, which can cause
allocations to do the dma mapping thing afaik. No?

Maybe there's some reason why that doesn't happen either, but
basically this whole callchain looks *way* to complicated to be used
under a core VM spinlock.

                Linus