Commit e623a48e authored Jul 20, 2017 by Håkon Bugge Committed by David S. Miller Jul 20, 2017

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: Håkon Bugge <haakon.bugge@oracle.com>
Reviewed-by: Knut Omang <knut.omang@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 070f9c65

net/rds/send.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -170,8 +170,8 @@ restart:
		* The acquire_in_xmit() check above ensures that only one
		* caller can increment c_send_gen at any time.
		*/
		cp->cp_send_gen++;
		send_gen = cp->cp_send_gen;
		send_gen = READ_ONCE(cp->cp_send_gen) + 1;
		WRITE_ONCE(cp->cp_send_gen, send_gen);

		/*
		* rds_conn_shutdown() sets the conn state and then tests RDS_IN_XMIT,
		@@ -431,7 +431,7 @@ over_batch:
		smp_mb();
		if ((test_bit(0, &conn->c_map_queued) \|\|
		!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);
		if (batch_count < send_batch_count)
		goto restart;

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