Date:   Sun, 23 Oct 2022 20:44:00 +0800
From:   "D.Wythe" <alibuda@...ux.alibaba.com>
To:     kgraul@...ux.ibm.com, wenjia@...ux.ibm.com, jaka@...ux.ibm.com
Cc:     kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: [PATCH net-next v4 08/10] net/smc: replace mutex rmbs_lock and sndbufs_lock with rw_semaphore

From: "D. Wythe" <alibuda@...ux.alibaba.com>

It's clear that rmbs_lock and sndbufs_lock are aims to protect the
rmbs list or the sndbufs list.

During connection establieshment, smc_buf_get_slot() will always
be invoked, and it only performs read semantics in rmbs list and
sndbufs list.

Based on the above considerations, we replace mutex with rw_semaphore.
Only smc_buf_get_slot() use down_read() to allow smc_buf_get_slot()
run concurrently, other part use down_write() to keep exclusive
semantics.

Signed-off-by: D. Wythe <alibuda@...ux.alibaba.com>
---
 net/smc/smc_core.c | 55 +++++++++++++++++++++++++++---------------------------
 net/smc/smc_core.h |  4 ++--
 net/smc/smc_llc.c  | 16 ++++++++--------
 3 files changed, 38 insertions(+), 37 deletions(-)

diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index 48ad76b..b09a3fd 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -1128,8 +1128,8 @@ static int smc_lgr_create(struct smc_sock *smc, struct smc_init_info *ini)
 	lgr->freeing = 0;
 	lgr->vlan_id = ini->vlan_id;
 	refcount_set(&lgr->refcnt, 1); /* set lgr refcnt to 1 */
-	mutex_init(&lgr->sndbufs_lock);
-	mutex_init(&lgr->rmbs_lock);
+	init_rwsem(&lgr->sndbufs_lock);
+	init_rwsem(&lgr->rmbs_lock);
 	rwlock_init(&lgr->conns_lock);
 	for (i = 0; i < SMC_RMBE_SIZES; i++) {
 		INIT_LIST_HEAD(&lgr->sndbufs[i]);
@@ -1375,7 +1375,7 @@ struct smc_link *smc_switch_conns(struct smc_link_group *lgr,
 static void smcr_buf_unuse(struct smc_buf_desc *buf_desc, bool is_rmb,
 			   struct smc_link_group *lgr)
 {
-	struct mutex *lock;	/* lock buffer list */
+	struct rw_semaphore *lock;	/* lock buffer list */
 	int rc;
 
 	if (is_rmb && buf_desc->is_conf_rkey && !list_empty(&lgr->list)) {
@@ -1395,9 +1395,9 @@ static void smcr_buf_unuse(struct smc_buf_desc *buf_desc, bool is_rmb,
 		/* buf registration failed, reuse not possible */
 		lock = is_rmb ? &lgr->rmbs_lock :
 				&lgr->sndbufs_lock;
-		mutex_lock(lock);
+		down_write(lock);
 		list_del(&buf_desc->list);
-		mutex_unlock(lock);
+		up_write(lock);
 
 		smc_buf_free(lgr, is_rmb, buf_desc);
 	} else {
@@ -1501,15 +1501,16 @@ static void smcr_buf_unmap_lgr(struct smc_link *lnk)
 	int i;
 
 	for (i = 0; i < SMC_RMBE_SIZES; i++) {
-		mutex_lock(&lgr->rmbs_lock);
+		down_write(&lgr->rmbs_lock);
 		list_for_each_entry_safe(buf_desc, bf, &lgr->rmbs[i], list)
 			smcr_buf_unmap_link(buf_desc, true, lnk);
-		mutex_unlock(&lgr->rmbs_lock);
-		mutex_lock(&lgr->sndbufs_lock);
+		up_write(&lgr->rmbs_lock);
+
+		down_write(&lgr->sndbufs_lock);
 		list_for_each_entry_safe(buf_desc, bf, &lgr->sndbufs[i],
 					 list)
 			smcr_buf_unmap_link(buf_desc, false, lnk);
-		mutex_unlock(&lgr->sndbufs_lock);
+		up_write(&lgr->sndbufs_lock);
 	}
 }
 
@@ -2328,19 +2329,19 @@ int smc_uncompress_bufsize(u8 compressed)
  * buffer size; if not available, return NULL
  */
 static struct smc_buf_desc *smc_buf_get_slot(int compressed_bufsize,
-					     struct mutex *lock,
+					     struct rw_semaphore *lock,
 					     struct list_head *buf_list)
 {
 	struct smc_buf_desc *buf_slot;
 
-	mutex_lock(lock);
+	down_read(lock);
 	list_for_each_entry(buf_slot, buf_list, list) {
 		if (cmpxchg(&buf_slot->used, 0, 1) == 0) {
-			mutex_unlock(lock);
+			up_read(lock);
 			return buf_slot;
 		}
 	}
-	mutex_unlock(lock);
+	up_read(lock);
 	return NULL;
 }
 
@@ -2449,13 +2450,13 @@ int smcr_link_reg_buf(struct smc_link *link, struct smc_buf_desc *buf_desc)
 	return 0;
 }
 
-static int _smcr_buf_map_lgr(struct smc_link *lnk, struct mutex *lock,
+static int _smcr_buf_map_lgr(struct smc_link *lnk, struct rw_semaphore *lock,
 			     struct list_head *lst, bool is_rmb)
 {
 	struct smc_buf_desc *buf_desc, *bf;
 	int rc = 0;
 
-	mutex_lock(lock);
+	down_write(lock);
 	list_for_each_entry_safe(buf_desc, bf, lst, list) {
 		if (!buf_desc->used)
 			continue;
@@ -2464,7 +2465,7 @@ static int _smcr_buf_map_lgr(struct smc_link *lnk, struct mutex *lock,
 			goto out;
 	}
 out:
-	mutex_unlock(lock);
+	up_write(lock);
 	return rc;
 }
 
@@ -2497,37 +2498,37 @@ int smcr_buf_reg_lgr(struct smc_link *lnk)
 	int i, rc = 0;
 
 	/* reg all RMBs for a new link */
-	mutex_lock(&lgr->rmbs_lock);
+	down_write(&lgr->rmbs_lock);
 	for (i = 0; i < SMC_RMBE_SIZES; i++) {
 		list_for_each_entry_safe(buf_desc, bf, &lgr->rmbs[i], list) {
 			if (!buf_desc->used)
 				continue;
 			rc = smcr_link_reg_buf(lnk, buf_desc);
 			if (rc) {
-				mutex_unlock(&lgr->rmbs_lock);
+				up_write(&lgr->rmbs_lock);
 				return rc;
 			}
 		}
 	}
-	mutex_unlock(&lgr->rmbs_lock);
+	up_write(&lgr->rmbs_lock);
 
 	if (lgr->buf_type == SMCR_PHYS_CONT_BUFS)
 		return rc;
 
 	/* reg all vzalloced sndbufs for a new link */
-	mutex_lock(&lgr->sndbufs_lock);
+	down_write(&lgr->sndbufs_lock);
 	for (i = 0; i < SMC_RMBE_SIZES; i++) {
 		list_for_each_entry_safe(buf_desc, bf, &lgr->sndbufs[i], list) {
 			if (!buf_desc->used || !buf_desc->is_vm)
 				continue;
 			rc = smcr_link_reg_buf(lnk, buf_desc);
 			if (rc) {
-				mutex_unlock(&lgr->sndbufs_lock);
+				up_write(&lgr->sndbufs_lock);
 				return rc;
 			}
 		}
 	}
-	mutex_unlock(&lgr->sndbufs_lock);
+	up_write(&lgr->sndbufs_lock);
 	return rc;
 }
 
@@ -2648,7 +2649,7 @@ static int __smc_buf_create(struct smc_sock *smc, bool is_smcd, bool is_rmb)
 	struct list_head *buf_list;
 	int bufsize, bufsize_short;
 	bool is_dgraded = false;
-	struct mutex *lock;	/* lock buffer list */
+	struct rw_semaphore *lock;	/* lock buffer list */
 	int sk_buf_size;
 
 	if (is_rmb)
@@ -2696,9 +2697,9 @@ static int __smc_buf_create(struct smc_sock *smc, bool is_smcd, bool is_rmb)
 		SMC_STAT_RMB_ALLOC(smc, is_smcd, is_rmb);
 		SMC_STAT_RMB_SIZE(smc, is_smcd, is_rmb, bufsize);
 		buf_desc->used = 1;
-		mutex_lock(lock);
+		down_write(lock);
 		list_add(&buf_desc->list, buf_list);
-		mutex_unlock(lock);
+		up_write(lock);
 		break; /* found */
 	}
 
@@ -2772,9 +2773,9 @@ int smc_buf_create(struct smc_sock *smc, bool is_smcd)
 	/* create rmb */
 	rc = __smc_buf_create(smc, is_smcd, true);
 	if (rc) {
-		mutex_lock(&smc->conn.lgr->sndbufs_lock);
+		down_write(&smc->conn.lgr->sndbufs_lock);
 		list_del(&smc->conn.sndbuf_desc->list);
-		mutex_unlock(&smc->conn.lgr->sndbufs_lock);
+		up_write(&smc->conn.lgr->sndbufs_lock);
 		smc_buf_free(smc->conn.lgr, false, smc->conn.sndbuf_desc);
 		smc->conn.sndbuf_desc = NULL;
 	}
diff --git a/net/smc/smc_core.h b/net/smc/smc_core.h
index 2a5a51b..7771462 100644
--- a/net/smc/smc_core.h
+++ b/net/smc/smc_core.h
@@ -260,9 +260,9 @@ struct smc_link_group {
 	unsigned short		vlan_id;	/* vlan id of link group */
 
 	struct list_head	sndbufs[SMC_RMBE_SIZES];/* tx buffers */
-	struct mutex		sndbufs_lock;	/* protects tx buffers */
+	struct rw_semaphore	sndbufs_lock;	/* protects tx buffers */
 	struct list_head	rmbs[SMC_RMBE_SIZES];	/* rx buffers */
-	struct mutex		rmbs_lock;	/* protects rx buffers */
+	struct rw_semaphore	rmbs_lock;	/* protects rx buffers */
 
 	u8			id[SMC_LGR_ID_SIZE];	/* unique lgr id */
 	struct delayed_work	free_work;	/* delayed freeing of an lgr */
diff --git a/net/smc/smc_llc.c b/net/smc/smc_llc.c
index edb0cef..4a010eb 100644
--- a/net/smc/smc_llc.c
+++ b/net/smc/smc_llc.c
@@ -642,7 +642,7 @@ static int smc_llc_fill_ext_v2(struct smc_llc_msg_add_link_v2_ext *ext,
 
 	prim_lnk_idx = link->link_idx;
 	lnk_idx = link_new->link_idx;
-	mutex_lock(&lgr->rmbs_lock);
+	down_write(&lgr->rmbs_lock);
 	ext->num_rkeys = lgr->conns_num;
 	if (!ext->num_rkeys)
 		goto out;
@@ -662,7 +662,7 @@ static int smc_llc_fill_ext_v2(struct smc_llc_msg_add_link_v2_ext *ext,
 	}
 	len += i * sizeof(ext->rt[0]);
 out:
-	mutex_unlock(&lgr->rmbs_lock);
+	up_write(&lgr->rmbs_lock);
 	return len;
 }
 
@@ -923,7 +923,7 @@ static int smc_llc_cli_rkey_exchange(struct smc_link *link,
 	int rc = 0;
 	int i;
 
-	mutex_lock(&lgr->rmbs_lock);
+	down_write(&lgr->rmbs_lock);
 	num_rkeys_send = lgr->conns_num;
 	buf_pos = smc_llc_get_first_rmb(lgr, &buf_lst);
 	do {
@@ -950,7 +950,7 @@ static int smc_llc_cli_rkey_exchange(struct smc_link *link,
 			break;
 	} while (num_rkeys_send || num_rkeys_recv);
 
-	mutex_unlock(&lgr->rmbs_lock);
+	up_write(&lgr->rmbs_lock);
 	return rc;
 }
 
@@ -1033,14 +1033,14 @@ static void smc_llc_save_add_link_rkeys(struct smc_link *link,
 	ext = (struct smc_llc_msg_add_link_v2_ext *)((u8 *)lgr->wr_rx_buf_v2 +
 						     SMC_WR_TX_SIZE);
 	max = min_t(u8, ext->num_rkeys, SMC_LLC_RKEYS_PER_MSG_V2);
-	mutex_lock(&lgr->rmbs_lock);
+	down_write(&lgr->rmbs_lock);
 	for (i = 0; i < max; i++) {
 		smc_rtoken_set(lgr, link->link_idx, link_new->link_idx,
 			       ext->rt[i].rmb_key,
 			       ext->rt[i].rmb_vaddr_new,
 			       ext->rt[i].rmb_key_new);
 	}
-	mutex_unlock(&lgr->rmbs_lock);
+	up_write(&lgr->rmbs_lock);
 }
 
 static void smc_llc_save_add_link_info(struct smc_link *link,
@@ -1347,7 +1347,7 @@ static int smc_llc_srv_rkey_exchange(struct smc_link *link,
 	int rc = 0;
 	int i;
 
-	mutex_lock(&lgr->rmbs_lock);
+	down_write(&lgr->rmbs_lock);
 	num_rkeys_send = lgr->conns_num;
 	buf_pos = smc_llc_get_first_rmb(lgr, &buf_lst);
 	do {
@@ -1372,7 +1372,7 @@ static int smc_llc_srv_rkey_exchange(struct smc_link *link,
 		smc_llc_flow_qentry_del(&lgr->llc_flow_lcl);
 	} while (num_rkeys_send || num_rkeys_recv);
 out:
-	mutex_unlock(&lgr->rmbs_lock);
+	up_write(&lgr->rmbs_lock);
 	return rc;
 }
 
-- 
1.8.3.1

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