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alistair23-linux/net/rxrpc/conn_service.c

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rxrpc: Split service connection code out into its own file Split the service-specific connection code out into into its own file. The client-specific code has already been split out. This will leave just the common code in the original file. Signed-off-by: David Howells <dhowells@redhat.com>
2016-04-04 07:00:40 -06:00
/* Service connection management
*
* Copyright (C) 2016 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#include <linux/slab.h>
#include "ar-internal.h"
rxrpc: Use RCU to access a peer's service connection tree Move to using RCU access to a peer's service connection tree when routing an incoming packet. This is done using a seqlock to trigger retrying of the tree walk if a change happened. Further, we no longer get a ref on the connection looked up in the data_ready handler unless we queue the connection's work item - and then only if the refcount > 0. Note that I'm avoiding the use of a hash table for service connections because each service connection is addressed by a 62-bit number (constructed from epoch and connection ID >> 2) that would allow the client to engage in bucket stuffing, given knowledge of the hash algorithm. Peers, however, are hashed as the network address is less controllable by the client. The total number of peers will also be limited in a future commit. Signed-off-by: David Howells <dhowells@redhat.com>
2016-07-01 00:51:50 -06:00
/*
* Find a service connection under RCU conditions.
*
* We could use a hash table, but that is subject to bucket stuffing by an
* attacker as the client gets to pick the epoch and cid values and would know
* the hash function. So, instead, we use a hash table for the peer and from
* that an rbtree to find the service connection. Under ordinary circumstances
* it might be slower than a large hash table, but it is at least limited in
* depth.
*/
struct rxrpc_connection *rxrpc_find_service_conn_rcu(struct rxrpc_peer *peer,
struct sk_buff *skb)
{
struct rxrpc_connection *conn = NULL;
struct rxrpc_conn_proto k;
struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
struct rb_node *p;
unsigned int seq = 0;
k.epoch = sp->hdr.epoch;
k.cid = sp->hdr.cid & RXRPC_CIDMASK;
do {
/* Unfortunately, rbtree walking doesn't give reliable results
* under just the RCU read lock, so we have to check for
* changes.
*/
read_seqbegin_or_lock(&peer->service_conn_lock, &seq);
p = rcu_dereference_raw(peer->service_conns.rb_node);
while (p) {
conn = rb_entry(p, struct rxrpc_connection, service_node);
if (conn->proto.index_key < k.index_key)
p = rcu_dereference_raw(p->rb_left);
else if (conn->proto.index_key > k.index_key)
p = rcu_dereference_raw(p->rb_right);
else
goto done;
conn = NULL;
}
} while (need_seqretry(&peer->service_conn_lock, seq));
done:
done_seqretry(&peer->service_conn_lock, seq);
_leave(" = %d", conn ? conn->debug_id : -1);
return conn;
}
/*
* Insert a service connection into a peer's tree, thereby making it a target
* for incoming packets.
*/
static struct rxrpc_connection *
rxrpc_publish_service_conn(struct rxrpc_peer *peer,
struct rxrpc_connection *conn)
{
struct rxrpc_connection *cursor = NULL;
struct rxrpc_conn_proto k = conn->proto;
struct rb_node **pp, *parent;
write_seqlock_bh(&peer->service_conn_lock);
pp = &peer->service_conns.rb_node;
parent = NULL;
while (*pp) {
parent = *pp;
cursor = rb_entry(parent,
struct rxrpc_connection, service_node);
if (cursor->proto.index_key < k.index_key)
pp = &(*pp)->rb_left;
else if (cursor->proto.index_key > k.index_key)
pp = &(*pp)->rb_right;
else
goto found_extant_conn;
}
rb_link_node_rcu(&conn->service_node, parent, pp);
rb_insert_color(&conn->service_node, &peer->service_conns);
conn_published:
set_bit(RXRPC_CONN_IN_SERVICE_CONNS, &conn->flags);
write_sequnlock_bh(&peer->service_conn_lock);
_leave(" = %d [new]", conn->debug_id);
return conn;
found_extant_conn:
if (atomic_read(&cursor->usage) == 0)
goto replace_old_connection;
write_sequnlock_bh(&peer->service_conn_lock);
/* We should not be able to get here. rxrpc_incoming_connection() is
* called in a non-reentrant context, so there can't be a race to
* insert a new connection.
*/
BUG();
replace_old_connection:
/* The old connection is from an outdated epoch. */
_debug("replace conn");
rb_replace_node_rcu(&cursor->service_node,
&conn->service_node,
&peer->service_conns);
clear_bit(RXRPC_CONN_IN_SERVICE_CONNS, &cursor->flags);
goto conn_published;
}
rxrpc: Split service connection code out into its own file Split the service-specific connection code out into into its own file. The client-specific code has already been split out. This will leave just the common code in the original file. Signed-off-by: David Howells <dhowells@redhat.com>
2016-04-04 07:00:40 -06:00
/*
* get a record of an incoming connection
*/
struct rxrpc_connection *rxrpc_incoming_connection(struct rxrpc_local *local,
rxrpc: Move peer lookup from call-accept to new-incoming-conn Move the lookup of a peer from a call that's being accepted into the function that creates a new incoming connection. This will allow us to avoid incrementing the peer's usage count in some cases in future. Note that I haven't bother to integrate rxrpc_get_addr_from_skb() with rxrpc_extract_addr_from_skb() as I'm going to delete the former in the very near future. Signed-off-by: David Howells <dhowells@redhat.com>
2016-06-29 07:40:39 -06:00
struct sockaddr_rxrpc *srx,
rxrpc: Split service connection code out into its own file Split the service-specific connection code out into into its own file. The client-specific code has already been split out. This will leave just the common code in the original file. Signed-off-by: David Howells <dhowells@redhat.com>
2016-04-04 07:00:40 -06:00
struct sk_buff *skb)
{
rxrpc: Use RCU to access a peer's service connection tree Move to using RCU access to a peer's service connection tree when routing an incoming packet. This is done using a seqlock to trigger retrying of the tree walk if a change happened. Further, we no longer get a ref on the connection looked up in the data_ready handler unless we queue the connection's work item - and then only if the refcount > 0. Note that I'm avoiding the use of a hash table for service connections because each service connection is addressed by a 62-bit number (constructed from epoch and connection ID >> 2) that would allow the client to engage in bucket stuffing, given knowledge of the hash algorithm. Peers, however, are hashed as the network address is less controllable by the client. The total number of peers will also be limited in a future commit. Signed-off-by: David Howells <dhowells@redhat.com>
2016-07-01 00:51:50 -06:00
struct rxrpc_connection *conn;
rxrpc: Split service connection code out into its own file Split the service-specific connection code out into into its own file. The client-specific code has already been split out. This will leave just the common code in the original file. Signed-off-by: David Howells <dhowells@redhat.com>
2016-04-04 07:00:40 -06:00
struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
rxrpc: Move peer lookup from call-accept to new-incoming-conn Move the lookup of a peer from a call that's being accepted into the function that creates a new incoming connection. This will allow us to avoid incrementing the peer's usage count in some cases in future. Note that I haven't bother to integrate rxrpc_get_addr_from_skb() with rxrpc_extract_addr_from_skb() as I'm going to delete the former in the very near future. Signed-off-by: David Howells <dhowells@redhat.com>
2016-06-29 07:40:39 -06:00
struct rxrpc_peer *peer;
rxrpc: Split service connection code out into its own file Split the service-specific connection code out into into its own file. The client-specific code has already been split out. This will leave just the common code in the original file. Signed-off-by: David Howells <dhowells@redhat.com>
2016-04-04 07:00:40 -06:00
const char *new = "old";
_enter("");
rxrpc: Move peer lookup from call-accept to new-incoming-conn Move the lookup of a peer from a call that's being accepted into the function that creates a new incoming connection. This will allow us to avoid incrementing the peer's usage count in some cases in future. Note that I haven't bother to integrate rxrpc_get_addr_from_skb() with rxrpc_extract_addr_from_skb() as I'm going to delete the former in the very near future. Signed-off-by: David Howells <dhowells@redhat.com>
2016-06-29 07:40:39 -06:00
peer = rxrpc_lookup_peer(local, srx, GFP_NOIO);
if (!peer) {
_debug("no peer");
return ERR_PTR(-EBUSY);
}
rxrpc: Split service connection code out into its own file Split the service-specific connection code out into into its own file. The client-specific code has already been split out. This will leave just the common code in the original file. Signed-off-by: David Howells <dhowells@redhat.com>
2016-04-04 07:00:40 -06:00
ASSERT(sp->hdr.flags & RXRPC_CLIENT_INITIATED);
rxrpc: Use RCU to access a peer's service connection tree Move to using RCU access to a peer's service connection tree when routing an incoming packet. This is done using a seqlock to trigger retrying of the tree walk if a change happened. Further, we no longer get a ref on the connection looked up in the data_ready handler unless we queue the connection's work item - and then only if the refcount > 0. Note that I'm avoiding the use of a hash table for service connections because each service connection is addressed by a 62-bit number (constructed from epoch and connection ID >> 2) that would allow the client to engage in bucket stuffing, given knowledge of the hash algorithm. Peers, however, are hashed as the network address is less controllable by the client. The total number of peers will also be limited in a future commit. Signed-off-by: David Howells <dhowells@redhat.com>
2016-07-01 00:51:50 -06:00
rcu_read_lock();
peer = rxrpc_lookup_peer_rcu(local, srx);
if (peer) {
conn = rxrpc_find_service_conn_rcu(peer, skb);
if (conn) {
if (sp->hdr.securityIndex != conn->security_ix)
goto security_mismatch_rcu;
if (rxrpc_get_connection_maybe(conn))
goto found_extant_connection_rcu;
/* The conn has expired but we can't remove it without
* the appropriate lock, so we attempt to replace it
* when we have a new candidate.
*/
}
if (!rxrpc_get_peer_maybe(peer))
peer = NULL;
rxrpc: Split service connection code out into its own file Split the service-specific connection code out into into its own file. The client-specific code has already been split out. This will leave just the common code in the original file. Signed-off-by: David Howells <dhowells@redhat.com>
2016-04-04 07:00:40 -06:00
}
rxrpc: Use RCU to access a peer's service connection tree Move to using RCU access to a peer's service connection tree when routing an incoming packet. This is done using a seqlock to trigger retrying of the tree walk if a change happened. Further, we no longer get a ref on the connection looked up in the data_ready handler unless we queue the connection's work item - and then only if the refcount > 0. Note that I'm avoiding the use of a hash table for service connections because each service connection is addressed by a 62-bit number (constructed from epoch and connection ID >> 2) that would allow the client to engage in bucket stuffing, given knowledge of the hash algorithm. Peers, however, are hashed as the network address is less controllable by the client. The total number of peers will also be limited in a future commit. Signed-off-by: David Howells <dhowells@redhat.com>
2016-07-01 00:51:50 -06:00
rcu_read_unlock();
rxrpc: Split service connection code out into its own file Split the service-specific connection code out into into its own file. The client-specific code has already been split out. This will leave just the common code in the original file. Signed-off-by: David Howells <dhowells@redhat.com>
2016-04-04 07:00:40 -06:00
rxrpc: Use RCU to access a peer's service connection tree Move to using RCU access to a peer's service connection tree when routing an incoming packet. This is done using a seqlock to trigger retrying of the tree walk if a change happened. Further, we no longer get a ref on the connection looked up in the data_ready handler unless we queue the connection's work item - and then only if the refcount > 0. Note that I'm avoiding the use of a hash table for service connections because each service connection is addressed by a 62-bit number (constructed from epoch and connection ID >> 2) that would allow the client to engage in bucket stuffing, given knowledge of the hash algorithm. Peers, however, are hashed as the network address is less controllable by the client. The total number of peers will also be limited in a future commit. Signed-off-by: David Howells <dhowells@redhat.com>
2016-07-01 00:51:50 -06:00
if (!peer) {
peer = rxrpc_lookup_peer(local, srx, GFP_NOIO);
if (IS_ERR(peer))
goto enomem;
rxrpc: Split service connection code out into its own file Split the service-specific connection code out into into its own file. The client-specific code has already been split out. This will leave just the common code in the original file. Signed-off-by: David Howells <dhowells@redhat.com>
2016-04-04 07:00:40 -06:00
}
rxrpc: Use RCU to access a peer's service connection tree Move to using RCU access to a peer's service connection tree when routing an incoming packet. This is done using a seqlock to trigger retrying of the tree walk if a change happened. Further, we no longer get a ref on the connection looked up in the data_ready handler unless we queue the connection's work item - and then only if the refcount > 0. Note that I'm avoiding the use of a hash table for service connections because each service connection is addressed by a 62-bit number (constructed from epoch and connection ID >> 2) that would allow the client to engage in bucket stuffing, given knowledge of the hash algorithm. Peers, however, are hashed as the network address is less controllable by the client. The total number of peers will also be limited in a future commit. Signed-off-by: David Howells <dhowells@redhat.com>
2016-07-01 00:51:50 -06:00
/* We don't have a matching record yet. */
conn = rxrpc_alloc_connection(GFP_NOIO);
if (!conn)
goto enomem_peer;
conn->proto.epoch = sp->hdr.epoch;
conn->proto.cid = sp->hdr.cid & RXRPC_CIDMASK;
conn->params.local = local;
conn->params.peer = peer;
conn->params.service_id = sp->hdr.serviceId;
conn->security_ix = sp->hdr.securityIndex;
conn->out_clientflag = 0;
conn->state = RXRPC_CONN_SERVICE;
if (conn->params.service_id)
conn->state = RXRPC_CONN_SERVICE_UNSECURED;
rxrpc: Split service connection code out into its own file Split the service-specific connection code out into into its own file. The client-specific code has already been split out. This will leave just the common code in the original file. Signed-off-by: David Howells <dhowells@redhat.com>
2016-04-04 07:00:40 -06:00
rxrpc: Use RCU to access a peer's service connection tree Move to using RCU access to a peer's service connection tree when routing an incoming packet. This is done using a seqlock to trigger retrying of the tree walk if a change happened. Further, we no longer get a ref on the connection looked up in the data_ready handler unless we queue the connection's work item - and then only if the refcount > 0. Note that I'm avoiding the use of a hash table for service connections because each service connection is addressed by a 62-bit number (constructed from epoch and connection ID >> 2) that would allow the client to engage in bucket stuffing, given knowledge of the hash algorithm. Peers, however, are hashed as the network address is less controllable by the client. The total number of peers will also be limited in a future commit. Signed-off-by: David Howells <dhowells@redhat.com>
2016-07-01 00:51:50 -06:00
rxrpc_get_local(local);
rxrpc: Split service connection code out into its own file Split the service-specific connection code out into into its own file. The client-specific code has already been split out. This will leave just the common code in the original file. Signed-off-by: David Howells <dhowells@redhat.com>
2016-04-04 07:00:40 -06:00
write_lock(&rxrpc_connection_lock);
list_add_tail(&conn->link, &rxrpc_connections);
write_unlock(&rxrpc_connection_lock);
rxrpc: Use RCU to access a peer's service connection tree Move to using RCU access to a peer's service connection tree when routing an incoming packet. This is done using a seqlock to trigger retrying of the tree walk if a change happened. Further, we no longer get a ref on the connection looked up in the data_ready handler unless we queue the connection's work item - and then only if the refcount > 0. Note that I'm avoiding the use of a hash table for service connections because each service connection is addressed by a 62-bit number (constructed from epoch and connection ID >> 2) that would allow the client to engage in bucket stuffing, given knowledge of the hash algorithm. Peers, however, are hashed as the network address is less controllable by the client. The total number of peers will also be limited in a future commit. Signed-off-by: David Howells <dhowells@redhat.com>
2016-07-01 00:51:50 -06:00
/* Make the connection a target for incoming packets. */
rxrpc_publish_service_conn(peer, conn);
rxrpc: Split service connection code out into its own file Split the service-specific connection code out into into its own file. The client-specific code has already been split out. This will leave just the common code in the original file. Signed-off-by: David Howells <dhowells@redhat.com>
2016-04-04 07:00:40 -06:00
new = "new";
success:
_net("CONNECTION %s %d {%x}", new, conn->debug_id, conn->proto.cid);
_leave(" = %p {u=%d}", conn, atomic_read(&conn->usage));
return conn;
rxrpc: Use RCU to access a peer's service connection tree Move to using RCU access to a peer's service connection tree when routing an incoming packet. This is done using a seqlock to trigger retrying of the tree walk if a change happened. Further, we no longer get a ref on the connection looked up in the data_ready handler unless we queue the connection's work item - and then only if the refcount > 0. Note that I'm avoiding the use of a hash table for service connections because each service connection is addressed by a 62-bit number (constructed from epoch and connection ID >> 2) that would allow the client to engage in bucket stuffing, given knowledge of the hash algorithm. Peers, however, are hashed as the network address is less controllable by the client. The total number of peers will also be limited in a future commit. Signed-off-by: David Howells <dhowells@redhat.com>
2016-07-01 00:51:50 -06:00
found_extant_connection_rcu:
rcu_read_unlock();
rxrpc: Split service connection code out into its own file Split the service-specific connection code out into into its own file. The client-specific code has already been split out. This will leave just the common code in the original file. Signed-off-by: David Howells <dhowells@redhat.com>
2016-04-04 07:00:40 -06:00
goto success;
rxrpc: Use RCU to access a peer's service connection tree Move to using RCU access to a peer's service connection tree when routing an incoming packet. This is done using a seqlock to trigger retrying of the tree walk if a change happened. Further, we no longer get a ref on the connection looked up in the data_ready handler unless we queue the connection's work item - and then only if the refcount > 0. Note that I'm avoiding the use of a hash table for service connections because each service connection is addressed by a 62-bit number (constructed from epoch and connection ID >> 2) that would allow the client to engage in bucket stuffing, given knowledge of the hash algorithm. Peers, however, are hashed as the network address is less controllable by the client. The total number of peers will also be limited in a future commit. Signed-off-by: David Howells <dhowells@redhat.com>
2016-07-01 00:51:50 -06:00
security_mismatch_rcu:
rcu_read_unlock();
rxrpc: Split service connection code out into its own file Split the service-specific connection code out into into its own file. The client-specific code has already been split out. This will leave just the common code in the original file. Signed-off-by: David Howells <dhowells@redhat.com>
2016-04-04 07:00:40 -06:00
_leave(" = -EKEYREJECTED");
return ERR_PTR(-EKEYREJECTED);
rxrpc: Use RCU to access a peer's service connection tree Move to using RCU access to a peer's service connection tree when routing an incoming packet. This is done using a seqlock to trigger retrying of the tree walk if a change happened. Further, we no longer get a ref on the connection looked up in the data_ready handler unless we queue the connection's work item - and then only if the refcount > 0. Note that I'm avoiding the use of a hash table for service connections because each service connection is addressed by a 62-bit number (constructed from epoch and connection ID >> 2) that would allow the client to engage in bucket stuffing, given knowledge of the hash algorithm. Peers, however, are hashed as the network address is less controllable by the client. The total number of peers will also be limited in a future commit. Signed-off-by: David Howells <dhowells@redhat.com>
2016-07-01 00:51:50 -06:00
enomem_peer:
rxrpc_put_peer(peer);
enomem:
_leave(" = -ENOMEM");
return ERR_PTR(-ENOMEM);
rxrpc: Split service connection code out into its own file Split the service-specific connection code out into into its own file. The client-specific code has already been split out. This will leave just the common code in the original file. Signed-off-by: David Howells <dhowells@redhat.com>
2016-04-04 07:00:40 -06:00
}
rxrpc: Maintain an extra ref on a conn for the cache list Overhaul the usage count accounting for the rxrpc_connection struct to make it easier to implement RCU access from the data_ready handler. The problem is that currently we're using a lock to prevent the garbage collector from trying to clean up a connection that we're contemplating unidling. We could just stick incoming packets on the connection we find, but we've then got a problem that we may race when dispatching a work item to process it as we need to give that a ref to prevent the rxrpc_connection struct from disappearing in the meantime. Further, incoming packets may get discarded if attached to an rxrpc_connection struct that is going away. Whilst this is not a total disaster - the client will presumably resend - it would delay processing of the call. This would affect the AFS client filesystem's service manager operation. To this end: (1) We now maintain an extra count on the connection usage count whilst it is on the connection list. This mean it is not in use when its refcount is 1. (2) When trying to reuse an old connection, we only increment the refcount if it is greater than 0. If it is 0, we replace it in the tree with a new candidate connection. (3) Two connection flags are added to indicate whether or not a connection is in the local's client connection tree (used by sendmsg) or the peer's service connection tree (used by data_ready). This makes sure that we don't try and remove a connection if it got replaced. The flags are tested under lock with the removal operation to prevent the reaper from killing the rxrpc_connection struct whilst someone else is trying to effect a replacement. This could probably be alleviated by using memory barriers between the flag set/test and the rb_tree ops. The rb_tree op would still need to be under the lock, however. (4) When trying to reap an old connection, we try to flip the usage count from 1 to 0. If it's not 1 at that point, then it must've come back to life temporarily and we ignore it. Signed-off-by: David Howells <dhowells@redhat.com>
2016-06-30 03:45:22 -06:00
/*
* Remove the service connection from the peer's tree, thereby removing it as a
* target for incoming packets.
*/
void rxrpc_unpublish_service_conn(struct rxrpc_connection *conn)
{
struct rxrpc_peer *peer = conn->params.peer;
rxrpc: Use RCU to access a peer's service connection tree Move to using RCU access to a peer's service connection tree when routing an incoming packet. This is done using a seqlock to trigger retrying of the tree walk if a change happened. Further, we no longer get a ref on the connection looked up in the data_ready handler unless we queue the connection's work item - and then only if the refcount > 0. Note that I'm avoiding the use of a hash table for service connections because each service connection is addressed by a 62-bit number (constructed from epoch and connection ID >> 2) that would allow the client to engage in bucket stuffing, given knowledge of the hash algorithm. Peers, however, are hashed as the network address is less controllable by the client. The total number of peers will also be limited in a future commit. Signed-off-by: David Howells <dhowells@redhat.com>
2016-07-01 00:51:50 -06:00
write_seqlock_bh(&peer->service_conn_lock);
rxrpc: Maintain an extra ref on a conn for the cache list Overhaul the usage count accounting for the rxrpc_connection struct to make it easier to implement RCU access from the data_ready handler. The problem is that currently we're using a lock to prevent the garbage collector from trying to clean up a connection that we're contemplating unidling. We could just stick incoming packets on the connection we find, but we've then got a problem that we may race when dispatching a work item to process it as we need to give that a ref to prevent the rxrpc_connection struct from disappearing in the meantime. Further, incoming packets may get discarded if attached to an rxrpc_connection struct that is going away. Whilst this is not a total disaster - the client will presumably resend - it would delay processing of the call. This would affect the AFS client filesystem's service manager operation. To this end: (1) We now maintain an extra count on the connection usage count whilst it is on the connection list. This mean it is not in use when its refcount is 1. (2) When trying to reuse an old connection, we only increment the refcount if it is greater than 0. If it is 0, we replace it in the tree with a new candidate connection. (3) Two connection flags are added to indicate whether or not a connection is in the local's client connection tree (used by sendmsg) or the peer's service connection tree (used by data_ready). This makes sure that we don't try and remove a connection if it got replaced. The flags are tested under lock with the removal operation to prevent the reaper from killing the rxrpc_connection struct whilst someone else is trying to effect a replacement. This could probably be alleviated by using memory barriers between the flag set/test and the rb_tree ops. The rb_tree op would still need to be under the lock, however. (4) When trying to reap an old connection, we try to flip the usage count from 1 to 0. If it's not 1 at that point, then it must've come back to life temporarily and we ignore it. Signed-off-by: David Howells <dhowells@redhat.com>
2016-06-30 03:45:22 -06:00
if (test_and_clear_bit(RXRPC_CONN_IN_SERVICE_CONNS, &conn->flags))
rb_erase(&conn->service_node, &peer->service_conns);
rxrpc: Use RCU to access a peer's service connection tree Move to using RCU access to a peer's service connection tree when routing an incoming packet. This is done using a seqlock to trigger retrying of the tree walk if a change happened. Further, we no longer get a ref on the connection looked up in the data_ready handler unless we queue the connection's work item - and then only if the refcount > 0. Note that I'm avoiding the use of a hash table for service connections because each service connection is addressed by a 62-bit number (constructed from epoch and connection ID >> 2) that would allow the client to engage in bucket stuffing, given knowledge of the hash algorithm. Peers, however, are hashed as the network address is less controllable by the client. The total number of peers will also be limited in a future commit. Signed-off-by: David Howells <dhowells@redhat.com>
2016-07-01 00:51:50 -06:00
write_sequnlock_bh(&peer->service_conn_lock);
rxrpc: Maintain an extra ref on a conn for the cache list Overhaul the usage count accounting for the rxrpc_connection struct to make it easier to implement RCU access from the data_ready handler. The problem is that currently we're using a lock to prevent the garbage collector from trying to clean up a connection that we're contemplating unidling. We could just stick incoming packets on the connection we find, but we've then got a problem that we may race when dispatching a work item to process it as we need to give that a ref to prevent the rxrpc_connection struct from disappearing in the meantime. Further, incoming packets may get discarded if attached to an rxrpc_connection struct that is going away. Whilst this is not a total disaster - the client will presumably resend - it would delay processing of the call. This would affect the AFS client filesystem's service manager operation. To this end: (1) We now maintain an extra count on the connection usage count whilst it is on the connection list. This mean it is not in use when its refcount is 1. (2) When trying to reuse an old connection, we only increment the refcount if it is greater than 0. If it is 0, we replace it in the tree with a new candidate connection. (3) Two connection flags are added to indicate whether or not a connection is in the local's client connection tree (used by sendmsg) or the peer's service connection tree (used by data_ready). This makes sure that we don't try and remove a connection if it got replaced. The flags are tested under lock with the removal operation to prevent the reaper from killing the rxrpc_connection struct whilst someone else is trying to effect a replacement. This could probably be alleviated by using memory barriers between the flag set/test and the rb_tree ops. The rb_tree op would still need to be under the lock, however. (4) When trying to reap an old connection, we try to flip the usage count from 1 to 0. If it's not 1 at that point, then it must've come back to life temporarily and we ignore it. Signed-off-by: David Howells <dhowells@redhat.com>
2016-06-30 03:45:22 -06:00
}
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