netdev - [PATCH net-next 2/4] net/tls: use RCU for the adder to the offload record list

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Date:   Fri,  6 Sep 2019 22:29:58 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, oss-drivers@...ronome.com,
        davejwatson@...com, borisp@...lanox.com, aviadye@...lanox.com,
        john.fastabend@...il.com, daniel@...earbox.net,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Dirk van der Merwe <dirk.vandermerwe@...ronome.com>
Subject: [PATCH net-next 2/4] net/tls: use RCU for the adder to the offload record list

All modifications to TLS record list happen under the socket
lock. Since records form an ordered queue readers are only
concerned about elements being removed, additions can happen
concurrently.

Use RCU primitives to ensure the correct access types
(READ_ONCE/WRITE_ONCE).

Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@...ronome.com>
---
 net/tls/tls_device.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/net/tls/tls_device.c b/net/tls/tls_device.c
index 285c9f9e94e4..b11355e00514 100644
--- a/net/tls/tls_device.c
+++ b/net/tls/tls_device.c
@@ -280,9 +280,7 @@ static int tls_push_record(struct sock *sk,
 
 	tls_append_frag(record, &dummy_tag_frag, prot->tag_size);
 	record->end_seq = tp->write_seq + record->len;
-	spin_lock_irq(&offload_ctx->lock);
-	list_add_tail(&record->list, &offload_ctx->records_list);
-	spin_unlock_irq(&offload_ctx->lock);
+	list_add_tail_rcu(&record->list, &offload_ctx->records_list);
 	offload_ctx->open_record = NULL;
 
 	if (test_bit(TLS_TX_SYNC_SCHED, &ctx->flags))
@@ -535,12 +533,16 @@ struct tls_record_info *tls_get_record(struct tls_offload_context_tx *context,
 		/* if retransmit_hint is irrelevant start
 		 * from the beggining of the list
 		 */
-		info = list_first_entry(&context->records_list,
-					struct tls_record_info, list);
+		info = list_first_entry_or_null(&context->records_list,
+						struct tls_record_info, list);
+		if (!info)
+			return NULL;
 		record_sn = context->unacked_record_sn;
 	}
 
-	list_for_each_entry_from(info, &context->records_list, list) {
+	/* We just need the _rcu for the READ_ONCE() */
+	rcu_read_lock();
+	list_for_each_entry_from_rcu(info, &context->records_list, list) {
 		if (before(seq, info->end_seq)) {
 			if (!context->retransmit_hint ||
 			    after(info->end_seq,
@@ -549,12 +551,15 @@ struct tls_record_info *tls_get_record(struct tls_offload_context_tx *context,
 				context->retransmit_hint = info;
 			}
 			*p_record_sn = record_sn;
-			return info;
+			goto exit_rcu_unlock;
 		}
 		record_sn++;
 	}
+	info = NULL;
 
-	return NULL;
+exit_rcu_unlock:
+	rcu_read_unlock();
+	return info;
 }
 EXPORT_SYMBOL(tls_get_record);
 
-- 
2.21.0