From: John Fastabend <john.fastabend@gmail.com>
To: David Miller <davem@davemloft.net>
Cc: jasowang@redhat.com, mst@redhat.com, john.r.fastabend@intel.com,
netdev@vger.kernel.org, alexei.starovoitov@gmail.com,
daniel@iogearbox.net
Subject: Re: [net PATCH v4 2/6] virtio_net: wrap rtnl_lock in test for calling with lock already held
Date: Tue, 17 Jan 2017 11:03:20 -0800 [thread overview]
Message-ID: <587E6A78.6020901@gmail.com> (raw)
In-Reply-To: <20170117.115733.428297564258724055.davem@davemloft.net>
On 17-01-17 08:57 AM, David Miller wrote:
> From: John Fastabend <john.fastabend@gmail.com>
> Date: Sun, 15 Jan 2017 15:59:47 -0800
>
>> @@ -2358,7 +2371,10 @@ static void remove_vq_common(struct virtnet_info *vi)
>> /* Free unused buffers in both send and recv, if any. */
>> free_unused_bufs(vi);
>>
>> - free_receive_bufs(vi);
>> + if (rtnl_is_locked())
>> + _free_receive_bufs(vi);
>> + else
>> + free_receive_bufs(vi);
>>
>> free_receive_page_frags(vi);
>>
>
> This doesn't work. rtnl_is_locked() doesn't tell if _you_ own the mutex, it
> just says that someone does.
>
> So if we now execute this code without taking the RTNL lock just because some
> other thread of control holds it, we introduce a race.
>
yeah this bit is junk. dang. Trying to get this locking right without duplicate
code or pushing around lock_me variables is getting tricky.
.John
next prev parent reply other threads:[~2017-01-17 19:03 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-15 23:59 [net PATCH v4 0/6] virtio_net XDP fixes and adjust_header support John Fastabend
2017-01-15 23:59 ` [net PATCH v4 1/6] virtio_net: use dev_kfree_skb for small buffer XDP receive John Fastabend
2017-01-15 23:59 ` [net PATCH v4 2/6] virtio_net: wrap rtnl_lock in test for calling with lock already held John Fastabend
2017-01-17 16:57 ` David Miller
2017-01-17 19:03 ` John Fastabend [this message]
2017-01-16 0:00 ` [net PATCH v4 3/6] virtio_net: factor out xdp handler for readability John Fastabend
2017-01-16 0:00 ` [net PATCH v4 4/6] virtio_net: remove duplicate queue pair binding in XDP John Fastabend
2017-01-16 0:01 ` [net PATCH v4 5/6] virtio: add pci_down/pci_up configuration John Fastabend
2017-01-16 3:57 ` Jason Wang
2017-01-16 4:04 ` John Fastabend
2017-01-17 18:45 ` John Fastabend
2017-01-16 0:01 ` [net PATCH v4 6/6] virtio_net: XDP support for adjust_head John Fastabend
2017-01-16 5:48 ` Jason Wang
2017-01-16 5:51 ` [net PATCH v4 0/6] virtio_net XDP fixes and adjust_header support Jason Wang
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