rds_cong_map_updated() runs after a peer's congestion map has been rewritten (by rds_tcp_cong_recv() and rds_ib_cong_recv(), or the clear-all in the loopback and IB send-completion paths). It bumps rds_cong_generation and then checks waitqueue_active() on map->m_waitq and on rds_poll_waitq to decide whether anyone needs waking. atomic_inc() carries no ordering and waitqueue_active() is a plain load, so nothing orders the map and generation stores before the wait queue reads. The waiters do the mirror image: rds_cong_wait() adds itself to m_waitq and then tests the port bit, and rds_poll() registers on rds_poll_waitq and then reads the generation. That is the store-buffering pattern described above waitqueue_active() in include/linux/wait.h - the updater can observe an empty wait queue while the waiter still observes the port as congested, and no wake-up is issued. rds_cong_wait() is an interruptible sleep with no timeout, so a sender blocked on a congested port stays blocked until the next congestion update from that peer arrives or a signal is delivered. A poll() waiter misses the map-updated notification the same way. Use wq_has_sleeper(), which is waitqueue_active() preceded by the required full barrier, as rds_tcp_state_change() already does for the same pattern. Fixes: 922cb17a5c81 ("RDS: Congestion-handling code") Assisted-by: Claude-Code:claude-fable-5 Signed-off-by: Allison Henderson --- Raised during review of "net/rds: own the fastpath locks across connection teardown", whose first patch fixes the same pattern in release_in_xmit(): https://lore.kernel.org/netdev/20260820133832.5384be37@kernel.org/ This patch is independent of that set and applies on its own. net/rds/cong.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/rds/cong.c b/net/rds/cong.c index 3133b91f9e69..f7634ce3ffc1 100644 --- a/net/rds/cong.c +++ b/net/rds/cong.c @@ -256,9 +256,9 @@ void rds_cong_map_updated(struct rds_cong_map *map, uint64_t portmask) map, &map->m_addr); rds_stats_inc(s_cong_update_received); atomic_inc(&rds_cong_generation); - if (waitqueue_active(&map->m_waitq)) + if (wq_has_sleeper(&map->m_waitq)) wake_up(&map->m_waitq); - if (waitqueue_active(&rds_poll_waitq)) + if (wq_has_sleeper(&rds_poll_waitq)) wake_up_all(&rds_poll_waitq); if (portmask && !list_empty(&rds_cong_monitor)) { base-commit: 4e15e89faac9f308baeb01f46c13a051814d2449 -- 2.25.1