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RDS: Rewrite rds_send_drop_to() for clarity 

This function has been the source of numerous bugs; it's just
too complicated. Simplified to nest spinlocks cleanly within
the second loop body, and kick out early if there are no
rms to drop.

This will be a little slower because conn lock is grabbed for
each entry instead of "caching" the lock across rms, but this
should be entirely irrelevant to fastpath performance.

Signed-off-by: Andy Grover <andy.grover@oracle.com>
This commit is contained in:
Andy Grover 2010-02-19 18:01:41 -08:00
parent 35b52c7053
commit 7c82eaf00e
1 changed files with 31 additions and 37 deletions
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68
net/rds/send.c
View File

@ -619,9 +619,8 @@ void rds_send_drop_to(struct rds_sock *rs, struct sockaddr_in *dest)
{
struct rds_message *rm, *tmp;
struct rds_connection *conn;
unsigned long flags, flags2;
unsigned long flags;
LIST_HEAD(list);
int wake = 0;
/* get all the messages we're dropping under the rs lock */
spin_lock_irqsave(&rs->rs_lock, flags);
@ -631,59 +630,54 @@ void rds_send_drop_to(struct rds_sock *rs, struct sockaddr_in *dest)
dest->sin_port != rm->m_inc.i_hdr.h_dport))
continue;
wake = 1;
list_move(&rm->m_sock_item, &list);
rds_send_sndbuf_remove(rs, rm);
clear_bit(RDS_MSG_ON_SOCK, &rm->m_flags);
}
/* order flag updates with the rs lock */
if (wake)
smp_mb__after_clear_bit();
smp_mb__after_clear_bit();
spin_unlock_irqrestore(&rs->rs_lock, flags);
conn = NULL;
if (list_empty(&list))
return;
/* now remove the messages from the conn list as needed */
/* Remove the messages from the conn */
list_for_each_entry(rm, &list, m_sock_item) {
/* We do this here rather than in the loop above, so that
* we don't have to nest m_rs_lock under rs->rs_lock */
spin_lock_irqsave(&rm->m_rs_lock, flags2);
/* If this is a RDMA operation, notify the app. */
conn = rm->m_inc.i_conn;
spin_lock_irqsave(&conn->c_lock, flags);
/*
* Maybe someone else beat us to removing rm from the conn.
* If we race with their flag update we'll get the lock and
* then really see that the flag has been cleared.
*/
if (!test_and_clear_bit(RDS_MSG_ON_CONN, &rm->m_flags)) {
spin_unlock_irqrestore(&conn->c_lock, flags);
continue;
}
/*
* Couldn't grab m_rs_lock in top loop (lock ordering),
* but we can now.
*/
spin_lock(&rm->m_rs_lock);
spin_lock(&rs->rs_lock);
__rds_rdma_send_complete(rs, rm, RDS_RDMA_CANCELED);
spin_unlock(&rs->rs_lock);
rm->m_rs = NULL;
spin_unlock_irqrestore(&rm->m_rs_lock, flags2);
spin_unlock(&rm->m_rs_lock);
/*
* If we see this flag cleared then we're *sure* that someone
* else beat us to removing it from the conn. If we race
* with their flag update we'll get the lock and then really
* see that the flag has been cleared.
*/
if (!test_bit(RDS_MSG_ON_CONN, &rm->m_flags))
continue;
if (conn != rm->m_inc.i_conn) {
if (conn)
spin_unlock_irqrestore(&conn->c_lock, flags);
conn = rm->m_inc.i_conn;
spin_lock_irqsave(&conn->c_lock, flags);
}
if (test_and_clear_bit(RDS_MSG_ON_CONN, &rm->m_flags)) {
list_del_init(&rm->m_conn_item);
rds_message_put(rm);
}
list_del_init(&rm->m_conn_item);
rds_message_put(rm);
spin_unlock_irqrestore(&conn->c_lock, flags);
}
if (conn)
spin_unlock_irqrestore(&conn->c_lock, flags);
if (wake)
rds_wake_sk_sleep(rs);
rds_wake_sk_sleep(rs);
while (!list_empty(&list)) {
rm = list_entry(list.next, struct rds_message, m_sock_item);