Another question on locking...

Robert Watson rwatson at
Sun Jun 29 17:56:41 PDT 2003

The locking in the -CURRENT tree for the socket stack is currently
incomplete; something we hope greatly to remedy on the way to 5.2-RELEASE. 
So currently all this code runs under the Giant lock, which is why it's

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert at      Network Associates Laboratories

On Sun, 29 Jun 2003, George V. Neville-Neil wrote:

> Hi,
> 	Looking at the code in uipc_socket.c and udp_usrreq.c I am a
> 	bit confused as to how the locking mechanism works between the
> 	sockets and the protocols.  The socket calls all occur under
> 	Giant, which the protocols do not deal with, and the protocols
> 	all lock on the inp mutex, which the socket calls do not deal
> 	with.  Furthermore the sblock/sbunlock calls are only use by
> 	the socket layer.  I'm reading udp_input() as it's simpler to
> 	follow.  Have I missed something?  What prevents a protocol
> 	from writing to a socket buffer at the wrong time or the
> 	socket code from tweaking it at the wrong time?  Is this
> 	handled simply because of the priority of the threads doing
> 	the work?
> Thanks,
> George
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