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Commit f9a2c80b authored by Ying Xue's avatar Ying Xue Committed by David S. Miller
Browse files

tipc: introduce new spinlock to protect struct link_req 



Currently, only 'bearer_lock' is used to protect struct link_req in
the function disc_timeout(). This is unsafe, since the member fields
'num_nodes' and 'timer_intv' might be accessed by below three different
threads simultaneously, none of them grabbing bearer_lock in the
critical region:

link_activate()
  tipc_bearer_add_dest()
    tipc_disc_add_dest()
      req->num_nodes++;

tipc_link_reset()
  tipc_bearer_remove_dest()
    tipc_disc_remove_dest()
      req->num_nodes--
      disc_update()
        read req->num_nodes
	write req->timer_intv

disc_timeout()
  read req->num_nodes
  read/write req->timer_intv

Without lock protection, the only symptom of a race is that discovery
messages occasionally may not be sent out. This is not fatal, since such
messages are best-effort anyway. On the other hand, since discovery
messages are not time critical, adding a protecting lock brings no
serious overhead either. So we add a new, dedicated spinlock in
order to guarantee absolute data consistency in link_req objects.
This also helps reduce the overall role of the bearer_lock, which
we want to remove completely in a later commit series.

Signed-off-by: default avatarYing Xue <ying.xue@windriver.com>
Reviewed-by: default avatarPaul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: default avatarJon Maloy <jon.maloy@ericsson.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent b9d4c339

net/tipc/discover.c

+9 −2
Original line number Diff line number Diff line
@@ -50,6 +50,7 @@ 
 * @dest: destination address for request messages

 * @domain: network domain to which links can be established

 * @num_nodes: number of nodes currently discovered (i.e. with an active link)

 * @lock: spinlock for controlling access to requests

 * @buf: request message to be (repeatedly) sent

 * @timer: timer governing period between requests

 * @timer_intv: current interval between requests (in ms)
@@ -59,6 +60,7 @@ struct tipc_link_req { 
	struct tipc_media_addr dest;

	u32 domain;

	int num_nodes;

	spinlock_t lock;

	struct sk_buff *buf;

	struct timer_list timer;

	unsigned int timer_intv;
@@ -274,7 +276,9 @@ static void disc_update(struct tipc_link_req *req) 
 */

void tipc_disc_add_dest(struct tipc_link_req *req)

{

	spin_lock_bh(&req->lock);

	req->num_nodes++;

	spin_unlock_bh(&req->lock);

}



/**
@@ -283,8 +287,10 @@ void tipc_disc_add_dest(struct tipc_link_req *req) 
 */

void tipc_disc_remove_dest(struct tipc_link_req *req)

{

	spin_lock_bh(&req->lock);

	req->num_nodes--;

	disc_update(req);

	spin_unlock_bh(&req->lock);

}



/**
@@ -297,7 +303,7 @@ static void disc_timeout(struct tipc_link_req *req) 
{

	int max_delay;



	spin_lock_bh(&req->bearer->lock);

	spin_lock_bh(&req->lock);



	/* Stop searching if only desired node has been found */

	if (tipc_node(req->domain) && req->num_nodes) {
@@ -325,7 +331,7 @@ static void disc_timeout(struct tipc_link_req *req) 


	k_start_timer(&req->timer, req->timer_intv);

exit:

	spin_unlock_bh(&req->bearer->lock);

	spin_unlock_bh(&req->lock);

}



/**
@@ -356,6 +362,7 @@ int tipc_disc_create(struct tipc_bearer *b_ptr, struct tipc_media_addr *dest, 
	req->domain = dest_domain;

	req->num_nodes = 0;

	req->timer_intv = TIPC_LINK_REQ_INIT;

	spin_lock_init(&req->lock);

	k_init_timer(&req->timer, (Handler)disc_timeout, (unsigned long)req);

	k_start_timer(&req->timer, req->timer_intv);

	b_ptr->link_req = req;