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Commit 86357b19 authored Oct 30, 2009 by Andy Grover Committed by David S. Miller Oct 30, 2009

RDS: Fix potential race around rds_i[bw]_allocation



"At rds_ib_recv_refill_one(), it first executes atomic_read(&rds_ib_allocation)
for if-condition checking,

and then executes atomic_inc(&rds_ib_allocation) if the condition was
not satisfied.

However, if any other code which updates rds_ib_allocation executes
between these two atomic operation executions,
it seems that it may result race condition. (especially when
rds_ib_allocation + 1 == rds_ib_sysctl_max_recv_allocation)"

This patch fixes this by using atomic_inc_unless to eliminate the
possibility of allocating more than rds_ib_sysctl_max_recv_allocation
and then decrementing the count if the allocation fails. It also
makes an identical change to the iwarp transport.

Reported-by: Shin Hong <hongshin@gmail.com>
Signed-off-by: Andy Grover <andy.grover@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 244546f0

net/rds/ib_recv.c

+4 −3

Original line number	Original line	Diff line number	Diff line
	@@ -143,15 +143,16 @@ static int rds_ib_recv_refill_one(struct rds_connection *conn,
	int ret = -ENOMEM;		int ret = -ENOMEM;

	if (recv->r_ibinc == NULL) {		if (recv->r_ibinc == NULL) {
	if (atomic_read(&rds_ib_allocation) >= rds_ib_sysctl_max_recv_allocation) {		if (!atomic_add_unless(&rds_ib_allocation, 1, rds_ib_sysctl_max_recv_allocation)) {
	rds_ib_stats_inc(s_ib_rx_alloc_limit);		rds_ib_stats_inc(s_ib_rx_alloc_limit);
	goto out;		goto out;
	}		}
	recv->r_ibinc = kmem_cache_alloc(rds_ib_incoming_slab,		recv->r_ibinc = kmem_cache_alloc(rds_ib_incoming_slab,
	kptr_gfp);		kptr_gfp);
	if (recv->r_ibinc == NULL)		if (recv->r_ibinc == NULL) {
			atomic_dec(&rds_ib_allocation);
	goto out;		goto out;
	atomic_inc(&rds_ib_allocation);		}
	INIT_LIST_HEAD(&recv->r_ibinc->ii_frags);		INIT_LIST_HEAD(&recv->r_ibinc->ii_frags);
	rds_inc_init(&recv->r_ibinc->ii_inc, conn, conn->c_faddr);		rds_inc_init(&recv->r_ibinc->ii_inc, conn, conn->c_faddr);
	}		}

net/rds/iw_recv.c

+4 −3

Original line number	Original line	Diff line number	Diff line
	@@ -143,15 +143,16 @@ static int rds_iw_recv_refill_one(struct rds_connection *conn,
	int ret = -ENOMEM;		int ret = -ENOMEM;

	if (recv->r_iwinc == NULL) {		if (recv->r_iwinc == NULL) {
	if (atomic_read(&rds_iw_allocation) >= rds_iw_sysctl_max_recv_allocation) {		if (!atomic_add_unless(&rds_iw_allocation, 1, rds_iw_sysctl_max_recv_allocation)) {
	rds_iw_stats_inc(s_iw_rx_alloc_limit);		rds_iw_stats_inc(s_iw_rx_alloc_limit);
	goto out;		goto out;
	}		}
	recv->r_iwinc = kmem_cache_alloc(rds_iw_incoming_slab,		recv->r_iwinc = kmem_cache_alloc(rds_iw_incoming_slab,
	kptr_gfp);		kptr_gfp);
	if (recv->r_iwinc == NULL)		if (recv->r_iwinc == NULL) {
			atomic_dec(&rds_iw_allocation);
	goto out;		goto out;
	atomic_inc(&rds_iw_allocation);		}
	INIT_LIST_HEAD(&recv->r_iwinc->ii_frags);		INIT_LIST_HEAD(&recv->r_iwinc->ii_frags);
	rds_inc_init(&recv->r_iwinc->ii_inc, conn, conn->c_faddr);		rds_inc_init(&recv->r_iwinc->ii_inc, conn, conn->c_faddr);
	}		}