Re: Locking down a socket, milestone 1

On Wed, 24 Apr 2002 10:18:01 -0400 (EDT),
  John Baldwin <[e-mail]> said:

jhb> On 24-Apr-2002 Seigo Tanimura wrote:
>> I am now working on locking down a socket.  (I have heard that Jeffrey
>> Hsu is also doing that, but I have never seen his patch.  Has anyone
>> seen that?) My first milestone patch is now available at:
>> 
>> 
>> http://people.FreeBSD.org/~tanimura/patches/socket_milestone1.diff.gz
>> 
>> 
>> The works I have done so far are:
>> 
>> 
>> - Determine the lock required to protect each of the members in struct
>> socket.
>> 
>> - Add mutexes to each of the sockbufs in a socket as BSD/OS does.
>> 
>> - Lock down so_count, so_options, so_linger and so_state.
>> 
>> - Add a global mutex socq_lock to protect the connection queues of a
>> listening socket.  Lock socq_lock to lock two sockets at once,
>> followed by enqueuing or dequeuing a socket, or moving a socket across
>> queues.  socq_lock is not an sx lock because we usually have to lock
>> two sockets to modify them.

jhb> Do you actually lock two sockets at once or do you lock one at a time while
jhb> holding socq_lock.  If you do lock two at once, what is the defined locking
jhb> order?

At the moment, I lock two sockets at once.  This is required, eg in
soisconnected() to move an accepting socket across the connection
queues of a listening socket.  The lock order is:

1. socq_lock
2. an accepting socket
3. a listening socket (in so_head of the accepting socket)

-- 
Seigo Tanimura <[e-mail]> <[e-mail]>

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