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Merge tag 'rxrpc-rewrite-20160706' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs
David Howells says:
====================
rxrpc: Improve conn/call lookup and fix call number generation [ver #3]
I've fixed a couple of patch descriptions and excised the patch that
duplicated the connections list for reconsideration at a later date.
For reference, the excised patch is sitting on the rxrpc-experimental
branch of my git tree, based on top of the rxrpc-rewrite branch. Diffing
it against yesterday's tag shows no differences.
Would you prefer the patch set to be emailed afresh instead of a git-pull
request?
David
---
Here's the next part of the AF_RXRPC rewrite. The two main purposes of
this set are to fix the call number handling and to make use of RCU when
looking up the connection or call to pass a received packet to.
Important changes in this set include:
(1) Avoidance of placing stack data into SG lists in rxkad so that kernel
stacks can become vmalloc'd (Herbert Xu).
(2) Calls cease pinning the connection they used as soon as possible,
which allows the connection to be discarded sooner and allows the call
channel on that connection to be reused earlier.
(3) Make each call channel on a connection have a separate and independent
call number space rather than having a shared number space for the
connection. Call numbers should increment monotonically per channel
on the client, and the server should ignore a call with a lower call
number for that channel than the latest it has seen. The RESPONSE
packet sets the minimum values of each call ID counter on a
connection.
(4) Look up calls by indexing the channel array on a connection rather
than by keeping calls in an rbtree on that connection. Also look up
calls using the channel array rather than using a hashtable.
The call hashtable can then be removed.
(5) Call terminal statuses are cached in the channel array for the last
call. It is assumed that if we the server have seen call N, then the
client no longer cares about call N-1 on the same channel.
This will allow retransmission of the terminal status in future
without the need to keep the rxrpc_call struct around.
(6) Peer lookups are moved out of common connection handling code and into
service connection handling code as client connections (a) must point
to a peer before they can be used and (b) are looked up by a
machine-unique connection ID directly, so we only need to look up the
peer first if we're going to deal with a service call.
(7) The reference count on a connection is held elevated by 1 whilst it is
alive (ie. idle unused connections have a refcount of 1). The reaper
will attempt to change the refcount from 1->0 and skip if this cannot
be done, whilst look ups only increment the refcount if it's non-zero.
This makes the implementation of RCU lookups easier as we don't have
to get a ref on the connection or a lock on the connection list to
prevent a connection being reaped whilst we're contemplating queueing
a packet that initiates a new service call upon it.
If we need to get a connection, but there's a dead connection in the
tree, we use rb_replace_node() to replace the dead one with a new one.
(8) Use a seqlock to validate the walk over the service connection rbtree
attached to a peer when it's being walked in RCU mode.
(9) Make the incoming call/connection packet handling code use RCU mode
and locks and make it only take a reference if the call/connection
gets queued on a workqueue.
The intention is that the next set will introduce the connection lifetime
management and capacity limits to prevent clients from overloading the
server.
There are some fixes too:
(1) Verifying that a packet coming in to a client connection came from the
expected source.
(2) Fix handling of connection failure in client call creation where we
don't reinitialise the list linkage block and a second attempt to
unlink the failed connection oopses and also we don't set the state
correctly, which causes an assertion failure.
(3) New service calls were being added to the socket's accept queue under
the wrong lock.
Changes:
(V2) In rxrpc_find_service_conn_rcu() initialised the sequence number to 0.
Fixed the RCU handling in conn_service.c by introducing and using
rb_replace_node_rcu() as an RCU-safe alternative in
rxrpc_publish_service_conn().
Modified and used rcu_dereference_raw() to avoid RCU sparse warnings
in rxrpc_find_service_conn_rcu().
Added in some missing RCU dereference wrappers. It seems to be
necessary to turn on CONFIG_PROVE_RCU_REPEATEDLY as well as
CONFIG_SPARSE_RCU_POINTER to get the static __rcu annotation checking
to happen.
Fixed some other sparse warnings, including a missing ntohs() in
jumbo packet processing.
(V3) Fixed some commit descriptions.
Excised the patch that duplicated the connection list to separate out
the procfs list for reconsideration at a later date.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>
cc3baecb21