From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
John Fastabend <john.fastabend@gmail.com>,
David Miller <davem@davemloft.net>
Subject: Re: [PATCH net-next 05/12] ptr_ring: disallow lockless __ptr_ring_full
Date: Mon, 29 Jan 2018 06:41:18 +0200 [thread overview]
Message-ID: <20180129064001-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <2c1b1348-08b3-a8b3-5d59-37db6257cda9@redhat.com>
On Mon, Jan 29, 2018 at 11:36:09AM +0800, Jason Wang wrote:
>
>
> On 2018年01月26日 10:46, Michael S. Tsirkin wrote:
> > > On 2018年01月26日 07:36, Michael S. Tsirkin wrote:
> > > > Similar to bcecb4bbf88a ("net: ptr_ring: otherwise safe empty checks can
> > > > overrun array bounds") a lockless use of __ptr_ring_full might
> > > > cause an out of bounds access.
> > > >
> > > > We can fix this, but it's easier to just disallow lockless
> > > > __ptr_ring_full for now.
> > > It looks to me that just fix this is better than disallow through doc (which
> > > is easily to be ignored ...).
> > >
> > > Thanks
> > lockless is tricky, and I'd rather not sprinkle READ/WRITE_ONCE where
> > they aren't necessary.
> >
>
> The problem is then API looks a little bit strange. Lockless were only
> allowed to be done at __ptr_ring_empty() but not __ptr_ring_full().
>
> Thanks
So __ptr_ring_empty doesn't really work lockless. It merely does not crash.
I don't believe we can do anything to remove the need to read the
docs unless people use the safe non __ variants.
--
MST
next prev parent reply other threads:[~2018-01-29 4:41 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-25 23:36 [PATCH net-next 00/12] ptr_ring fixes Michael S. Tsirkin
2018-01-25 23:36 ` [PATCH net-next 01/12] ptr_ring: keep consumer_head valid at all times Michael S. Tsirkin
2018-01-26 0:11 ` John Fastabend
2018-01-25 23:36 ` [PATCH net-next 02/12] ptr_ring: clean up documentation Michael S. Tsirkin
2018-01-25 23:36 ` [PATCH net-next 03/12] ptr_ring: READ/WRITE_ONCE for __ptr_ring_empty Michael S. Tsirkin
2018-01-26 2:37 ` Jason Wang
2018-01-26 2:44 ` Michael S. Tsirkin
2018-01-26 3:19 ` Jason Wang
2018-01-26 13:44 ` Michael S. Tsirkin
2018-01-25 23:36 ` [PATCH net-next 04/12] tap: fix use-after-free Michael S. Tsirkin
2018-01-25 23:36 ` [PATCH net-next 05/12] ptr_ring: disallow lockless __ptr_ring_full Michael S. Tsirkin
2018-01-26 2:38 ` Jason Wang
2018-01-26 2:46 ` Michael S. Tsirkin
2018-01-29 3:36 ` Jason Wang
2018-01-29 4:41 ` Michael S. Tsirkin [this message]
2018-01-29 7:09 ` Jason Wang
2018-01-25 23:36 ` [PATCH net-next 06/12] Revert "net: ptr_ring: otherwise safe empty checks can overrun array bounds" Michael S. Tsirkin
2018-01-26 0:12 ` John Fastabend
2018-01-25 23:36 ` [PATCH net-next 07/12] skb_array: use __ptr_ring_empty Michael S. Tsirkin
2018-01-25 23:36 ` [PATCH net-next 08/12] ptr_ring: prevent queue load/store tearing Michael S. Tsirkin
2018-01-26 2:38 ` Jason Wang
2018-01-26 2:49 ` Michael S. Tsirkin
2018-01-25 23:36 ` [PATCH net-next 09/12] tools/virtio: switch to __ptr_ring_empty Michael S. Tsirkin
2018-01-25 23:36 ` [PATCH net-next 10/12] tools/virtio: more stubs to fix tools build Michael S. Tsirkin
2018-01-25 23:36 ` [PATCH net-next 11/12] tools/virtio: copy READ/WRITE_ONCE Michael S. Tsirkin
2018-01-25 23:36 ` [PATCH net-next 12/12] tools/virtio: fix smp_mb on x86 Michael S. Tsirkin
2018-01-26 3:56 ` Jason Wang
2018-01-26 13:45 ` Michael S. Tsirkin
2018-01-26 3:20 ` [PATCH net-next 00/12] ptr_ring fixes Jason Wang
2018-01-29 7:10 ` Jason Wang
2018-01-29 17:03 ` David Miller
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