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From: Ka-Cheong Poon <ka-cheong.poon@oracle.com>
To: Eric Dumazet <edumazet@google.com>,
	"David S . Miller" <davem@davemloft.net>
Cc: netdev <netdev@vger.kernel.org>,
	Andy Lutomirski <luto@kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	Soheil Hassas Yeganeh <soheil@google.com>
Subject: Re: [PATCH v2 net-next 1/2] tcp: add TCP_ZEROCOPY_RECEIVE support for zerocopy receive
Date: Thu, 26 Apr 2018 21:40:14 +0800	[thread overview]
Message-ID: <d3ad6970-4139-76a9-2417-3df077753aa9@oracle.com> (raw)
In-Reply-To: <20180425214307.159264-2-edumazet@google.com>

On 04/26/2018 05:43 AM, Eric Dumazet wrote:
> When adding tcp mmap() implementation, I forgot that socket lock
> had to be taken before current->mm->mmap_sem. syzbot eventually caught
> the bug.
> 
> Since we can not lock the socket in tcp mmap() handler we have to
> split the operation in two phases.
> 
> 1) mmap() on a tcp socket simply reserves VMA space, and nothing else.
>    This operation does not involve any TCP locking.
> 
> 2) setsockopt(fd, IPPROTO_TCP, TCP_ZEROCOPY_RECEIVE, ...) implements
>   the transfert of pages from skbs to one VMA.
>    This operation only uses down_read(&current->mm->mmap_sem) after
>    holding TCP lock, thus solving the lockdep issue.


A quick question.  Is it a normal practice to return a result
in setsockopt() given that the optval parameter is supposed to
be a const void *?




-- 
K. Poon
ka-cheong.poon@oracle.com

  reply	other threads:[~2018-04-26 13:40 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-25 21:43 [PATCH v2 net-next 0/2] tcp: mmap: rework " Eric Dumazet
2018-04-25 21:43 ` [PATCH v2 net-next 1/2] tcp: add TCP_ZEROCOPY_RECEIVE support for " Eric Dumazet
2018-04-26 13:40   ` Ka-Cheong Poon [this message]
2018-04-26 13:47     ` Eric Dumazet
2018-04-27  8:44   ` kbuild test robot
2018-04-27 13:03     ` Eric Dumazet
2018-04-25 21:43 ` [PATCH v2 net-next 2/2] selftests: net: tcp_mmap must use TCP_ZEROCOPY_RECEIVE Eric Dumazet
2018-04-26  1:20 ` [PATCH v2 net-next 0/2] tcp: mmap: rework zerocopy receive Soheil Hassas Yeganeh
2018-04-26 14:56   ` Eric Dumazet
2018-04-26 21:16     ` Andy Lutomirski
2018-04-26 21:40       ` Eric Dumazet

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