Re: [PATCH] refcount: introduce refcount_is_one() helper function

[yajun . deng]

November 18, 2021 3:42 PM, "Peter Zijlstra" <peterz@xxxxxxxxxxxxx> wrote:

> On Thu, Nov 18, 2021 at 11:53:28AM +0800, Yajun Deng wrote:
> 
>> There are many cases where it is necessary to determine if refcount is one,
>> introduce refcount_is_one() helper function for these cases.
> 
> Give me one that is not racy?

The following determine refcount is one, 35 count.
linux (next-20211117) $ grep "refcount_read.*== 1"  ./  -RnI
./tools/lib/perf/mmap.c:              101:	    if (refcount_read(&map->refcnt) == 1 && perf_mmap__empty(map))
./tools/perf/tests/cpumap.c:           72:      TEST_ASSERT_VAL("wrong refcnt", refcount_read(&map->refcnt) == 1);
./tools/perf/tests/thread-map.c:       42:		refcount_read(&map->refcnt) == 1);
./tools/perf/tests/thread-map.c:       57:		refcount_read(&map->refcnt) == 1);
./tools/perf/tests/thread-map.c:       84:	    refcount_read(&threads->refcnt) == 1);
./tools/perf/tests/maps.c:             28:		TEST_ASSERT_VAL("wrong map refcnt", refcount_read(&map->refcnt) == 1);
./include/linux/skbuff.h:            1078:	    if (likely(refcount_read(&skb->users) == 1))
./include/net/sock.h:                 726:		WARN_ON(refcount_read(&sk->sk_refcnt) == 1);
./include/net/sock.h:                 748:		WARN_ON(refcount_read(&sk->sk_refcnt) == 1);
./net/core/neighbour.c:               214:	    if (refcount_read(&n->refcnt) == 1) {
./net/core/neighbour.c:               264:		if (refcount_read(&n->refcnt) == 1) {
./net/core/neighbour.c:               965:		if (refcount_read(&n->refcnt) == 1 &&
./net/core/dev.c:                    3017:	    if (likely(refcount_read(&skb->users) == 1)) {
./net/core/skbuff.c:                  710:		if (refcount_read(&fclones->fclone_ref) == 1)
./net/core/skbuff.c:                 1514:	    refcount_read(&fclones->fclone_ref) == 1) {
./net/core/skbuff.c:                 6278:	    if (refcount_read(&old->refcnt) == 1)
./net/core/skbuff.c:                 6402:		refcount_read(&ext->refcnt) == 1) {
./net/core/skbuff.c:                 6417:	    if (refcount_read(&ext->refcnt) == 1)
./net/netlink/af_netlink.c:           614:		WARN_ON(refcount_read(&sk->sk_refcnt) == 1);
./net/tipc/socket.c:                 3032:		WARN_ON(refcount_read(&sk->sk_refcnt) == 1);
./net/netfilter/ipvs/ip_vs_conn.c:    480:	    (refcount_read(&cp->refcnt) == 1) &&
./net/sctp/auth.c:998:	    refcount_read(&key->refcnt) == 1) {
./drivers/tty/serial/sb1250-duart.c:  698:	    if (refcount_read(&duart->map_guard) == 1) {
./drivers/infiniband/core/cm.c:      1048:	    WARN_ON(refcount_read(&cm_id_priv->refcount) == 1);
./drivers/infiniband/hw/irdma/utils.c:513:		refcount_read(&cqp_request->refcnt) == 1, 1000);
./drivers/crypto/caam/qi.c:           306:		if (refcount_read(&drv_ctx->refcnt) == 1)
./drivers/net/ethernet/mellanox/mlx5/core/fs_core.c:1633:		if (refcount_read(&handle->rule[i]->node.refcount) == 1) {
./drivers/net/vxlan.c:               1537:	    if (family == AF_INET && sock4 && refcount_read(&sock4->refcnt) == 1)
./drivers/net/vxlan.c:               1541:	    if (family == AF_INET6 && sock6 && refcount_read(&sock6->refcnt) == 1)
./kernel/events/core.c:             12861:		wait_var_event(&ctx->refcount, refcount_read(&ctx->refcount) == 1);
./fs/nfs/nfs4proc.c:                 9127:		if (refcount_read(&clp->cl_count) == 1)
./fs/lockd/mon.c:                     195:	    if (refcount_read(&nsm->sm_count) == 1
./fs/btrfs/transaction.c:            2061:	    ASSERT(refcount_read(&trans->use_count) == 1);
./fs/btrfs/block-group.c:            3960:		ASSERT(refcount_read(&block_group->refs) == 1);
./fs/afs/write.c:                     921:	    if (refcount_read(&wbk->usage) == 1)

The following determine refcount isn't one, 19 count.
linux (next-20211117) $ grep "refcount_read.*!= 1"  ./  -RnI
./include/linux/skbuff.h:                                1762:	return refcount_read(&skb->users) != 1;
./include/net/sock.h:                                    1297:	if (refcount_read(&sk->sk_refcnt) != 1)
./crypto/algapi.c:                                        461:	BUG_ON(refcount_read(&alg->cra_refcnt) != 1);
./crypto/algapi.c:                                        560:	BUG_ON(refcount_read(&inst->alg.cra_refcnt) != 1);
./net/sunrpc/auth.c:                                      690:	if (refcount_read(&cred->cr_count) != 1 ||
./net/llc/llc_conn.c:                                     977:	if (refcount_read(&sk->sk_refcnt) != 1) {
./net/ceph/osd_client.c:                                 5297:	WARN_ON(refcount_read(&osdc->homeless_osd.o_ref) != 1);
./net/ipv6/ip6_fib.c:                                    1037:	if (refcount_read(&rt->fib6_ref) != 1) {
./net/core/neighbour.c:                                   349:	if (refcount_read(&n->refcnt) != 1) {
./net/core/pktgen.c:                                     3430:	while (refcount_read(&(pkt_dev->skb->users)) != 1) {
./drivers/crypto/marvell/octeontx/otx_cptvf_algs.c:      1584:	if (refcount_read(&otx_cpt_skciphers[i].base.cra_refcnt) != 1)
./drivers/crypto/marvell/octeontx/otx_cptvf_algs.c:      1587:	if (refcount_read(&otx_cpt_aeads[i].base.cra_refcnt) != 1)
./drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_atcam.c:406:		refcount_read(&lkey_id->refcnt) != 1, lkey_id->id,
./drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_atcam.c:435:			     refcount_read(&lkey_id->refcnt) != 1,
./drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_atcam.c:464:			     refcount_read(&lkey_id->refcnt) != 1, lkey_id->id,
./drivers/block/nbd.c:                                    2541:		if (refcount_read(&nbd->refs) != 1)
./fs/exec.c:                                              1182:	if (refcount_read(&oldsighand->count) != 1) {
./fs/btrfs/tests/extent-map-tests.c:                        24:		if (refcount_read(&em->refs) != 1) {
./arch/s390/mm/extmem.c:                                   472:	if (refcount_read(&seg->ref_count) != 1) {