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Commit e623a48e authored by Håkon Bugge's avatar Håkon Bugge Committed by David S. Miller
Browse files

rds: Make sure updates to cp_send_gen can be observed 



cp->cp_send_gen is treated as a normal variable, although it may be
used by different threads.

This is fixed by using {READ,WRITE}_ONCE when it is incremented and
READ_ONCE when it is read outside the {acquire,release}_in_xmit
protection.

Normative reference from the Linux-Kernel Memory Model:

    Loads from and stores to shared (but non-atomic) variables should
    be protected with the READ_ONCE(), WRITE_ONCE(), and
    ACCESS_ONCE().

Clause 5.1.2.4/25 in the C standard is also relevant.

Signed-off-by: default avatarHåkon Bugge <haakon.bugge@oracle.com>
Reviewed-by: default avatarKnut Omang <knut.omang@oracle.com>
Acked-by: default avatarSantosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 070f9c65

net/rds/send.c

+3 −3
Original line number Original line Diff line number Diff line
@@ -170,8 +170,8 @@ int rds_send_xmit(struct rds_conn_path *cp) 
	 * The acquire_in_xmit() check above ensures that only one

	 * The acquire_in_xmit() check above ensures that only one

	 * caller can increment c_send_gen at any time.

	 * caller can increment c_send_gen at any time.

	 */

	 */

	cp->cp_send_gen++;

	send_gen = READ_ONCE(cp->cp_send_gen) + 1;

	send_gen = cp->cp_send_gen;

	WRITE_ONCE(cp->cp_send_gen, send_gen);





	/*

	/*

	 * rds_conn_shutdown() sets the conn state and then tests RDS_IN_XMIT,

	 * rds_conn_shutdown() sets the conn state and then tests RDS_IN_XMIT,
@@ -431,7 +431,7 @@ int rds_send_xmit(struct rds_conn_path *cp) 
		smp_mb();

		smp_mb();

		if ((test_bit(0, &conn->c_map_queued) ||

		if ((test_bit(0, &conn->c_map_queued) ||

		     !list_empty(&cp->cp_send_queue)) &&

		     !list_empty(&cp->cp_send_queue)) &&

		    send_gen == cp->cp_send_gen) {

			send_gen == READ_ONCE(cp->cp_send_gen)) {

			rds_stats_inc(s_send_lock_queue_raced);

			rds_stats_inc(s_send_lock_queue_raced);

			if (batch_count < send_batch_count)

			if (batch_count < send_batch_count)

				goto restart;

				goto restart;