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From: Christoph Hellwig <hch@infradead.org>
To: Eric Dumazet <edumazet@google.com>
Cc: "David S . Miller" <davem@davemloft.net>,
	netdev <netdev@vger.kernel.org>,
	Andy Lutomirski <luto@kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	Soheil Hassas Yeganeh <soheil@google.com>,
	Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH net-next 1/2] tcp: add TCP_ZEROCOPY_RECEIVE support for zerocopy receive
Date: Tue, 24 Apr 2018 23:28:59 -0700	[thread overview]
Message-ID: <20180425062859.GA23914@infradead.org> (raw)
In-Reply-To: <20180425052722.73022-2-edumazet@google.com>

On Tue, Apr 24, 2018 at 10:27:21PM -0700, 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.
> 
> This new implementation was suggested by Andy Lutomirski with great details.

Thanks, this looks much more sensible to me.

  reply	other threads:[~2018-04-25  6:29 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-25  5:27 [PATCH net-next 0/2] tcp: mmap: rework zerocopy receive Eric Dumazet
2018-04-25  5:27 ` [PATCH net-next 1/2] tcp: add TCP_ZEROCOPY_RECEIVE support for " Eric Dumazet
2018-04-25  6:28   ` Christoph Hellwig [this message]
2018-04-25 13:01     ` Eric Dumazet
2018-04-25 15:24       ` Christoph Hellwig
2018-04-25 16:04       ` Matthew Wilcox
2018-04-25 16:20         ` Eric Dumazet
2018-04-25 16:30           ` Matthew Wilcox
2018-04-25 16:22         ` Andy Lutomirski
2018-04-25 16:35           ` Eric Dumazet
2018-04-25 16:44             ` Eric Dumazet
2018-04-25 13:42   ` Eric Dumazet
2018-04-25  5:27 ` [PATCH net-next 2/2] selftests: net: tcp_mmap must use TCP_ZEROCOPY_RECEIVE Eric Dumazet

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