Subject: [PATCH net v2] rds: introduce acquire/release ordering in acquire/release_in_xmit()

From: Yewon Choi <[email-masked]>
Date: Fri, 15 Mar 2024 18:28:38 +0900

acquire/release_in_xmit() work as bit lock in rds_send_xmit(), so they
are expected to ensure acquire/release memory ordering semantics.
However, test_and_set_bit/clear_bit() don't imply such semantics, on
top of this, following smp_mb__after_atomic() does not guarantee release
ordering (memory barrier actually should be placed before clear_bit()).

Instead, we use clear_bit_unlock/test_and_set_bit_lock() here.

Fixes: 0f4b1c7e89e6 ("rds: fix rds_send_xmit() serialization")
Fixes: 1f9ecd7eacfd ("RDS: Pass rds_conn_path to rds_send_xmit()")
Signed-off-by: Yewon Choi <[email-masked]>
---
Changes in v1 -> v2:
- Added missing Fixes tags

 net/rds/send.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/rds/send.c b/net/rds/send.c
index 5e57a1581dc6..8f38009721b7 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -103,13 +103,12 @@ EXPORT_SYMBOL_GPL(rds_send_path_reset);
 
 static int acquire_in_xmit(struct rds_conn_path *cp)
 {
-	return test_and_set_bit(RDS_IN_XMIT, &cp->cp_flags) == 0;
+	return test_and_set_bit_lock(RDS_IN_XMIT, &cp->cp_flags) == 0;
 }
 
 static void release_in_xmit(struct rds_conn_path *cp)
 {
-	clear_bit(RDS_IN_XMIT, &cp->cp_flags);
-	smp_mb__after_atomic();
+	clear_bit_unlock(RDS_IN_XMIT, &cp->cp_flags);
 	/*
 	 * We don't use wait_on_bit()/wake_up_bit() because our waking is in a
 	 * hot path and finding waiters is very rare.  We don't want to walk
-- 
2.43.0