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Date: Sat, 29 Apr 2017 03:46:47 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Ding Tianhong <dingtianhong@huawei.com>
Cc: David Miller <davem@davemloft.net>, pabeni@redhat.com,
        edumazet@google.com, hannes@stressinduktion.org,
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        LinuxArm <linuxarm@huawei.com>,
        "weiyongjun (A)" <weiyongjun1@huawei.com>
Subject: Re: [PATCH v2] iov_iter: don't revert iov buffer if csum error
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On Sat, Apr 29, 2017 at 10:38:48AM +0800, Ding Tianhong wrote:
> The patch 327868212381 (make skb_copy_datagram_msg() et.al. preserve
> ->msg_iter on error) will revert the iov buffer if copy to iter
> failed, but it didn't copy any datagram if the skb_checksum_complete
> error, so no need to revert any data at this place.

The bug is real, but I would suggest a simpler fix:
                if (__skb_checksum_complete(skb))
                        return -EINVAL;
leaving the rest as-is.