The updated socket patch and axing sotryfree() (Re: Locking down a soc

On Wed, 24 Apr 2002 20:08:56 +0900,
  Seigo Tanimura <[e-mail]> said:

tanimura> I am now working on locking down a socket.  (I have heard that Jeffrey
tanimura> Hsu is also doing that, but I have never seen his patch.  Has anyone
tanimura> seen that?) My first milestone patch is now available at:

I updated the patch slightly, found at

http://people.FreeBSD.org/~tanimura/patches/socket_milestone1b.diff.gz

tanimura> The works I have done so far are:


tanimura> - Determine the lock required to protect each of the members in struct
tanimura>   socket.

tanimura> - Add mutexes to each of the sockbufs in a socket as BSD/OS does.

tanimura> - Lock down so_count, so_options, so_linger and so_state.

tanimura> - Add a global mutex socq_lock to protect the connection queues of a
tanimura>   listening socket.  Lock socq_lock to lock two sockets at once,
tanimura>   followed by enqueuing or dequeuing a socket, or moving a socket across
tanimura>   queues.  socq_lock is not an sx lock because we usually have to lock
tanimura>   two sockets to modify them.

This is reverted.  I cleaned up soisconnected() to avoid locking two
sockets at once.

*_locked() functions and macros no longer exist.  The following
functions and macros require a socket lock:

o soref(), sorele(), sotryfree()
o so[rw]wakeup()


I would like to commit this patch in one or two weeks to start working
on a possible race between a user process and a netisr kthread,
prevented by only the Giant lock at the moment.

When a user process calls sofree() for a listening socket, it attempts
to free the sockets in the connection queues by soabort().  If the
connection of an aborting socket gets dropped by a remote host (eg by
TCP RST), a netisr kthread also attempts to free the socket.  Since
the reference count of a socket in a connection queue is zero, this
would resust in doubly freeing a socket.

To solve that problem, I would like to axe sotryfree().  The PCB of a
socket and a connection queue should hold a reference to the
socket. This should make the reference count of an alive socket always
be >= 1, and ensure that there is only one referer to a socket to be
freed.

Comments?

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

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