From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 389FE3B95F9; Sun, 27 Sep 2026 06:14:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790489693; cv=none; b=i8H8Wypfud5pXUCob/fe0TuU1DgJ1FbOZ3k0i7fqr2Z8TgBG/fMkA0J+LgeCD6zExXm3hvkMX8NdPQrbqjnBGP/KIXmnWkuvelw7cY00hRi4YEYYK2P7B/oUmQ9VR5F08JLvK5UUgfcbQBdB+KMfK0/41SoWO2U+ce0B2/Z/0kE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790489693; c=relaxed/simple; bh=AqjAzHuloTbPu6A++zLbzKDGHFwYJeppDoNN20LsS5E=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=huc+p8LVdG+wbs3wyK6BpN7/yay7WcAigIiIhwHQVC3A13pRQpibXWeFKS515g7F57PlYqvYmPf02+b1PXjaIj5UDSVhm0Kf0V2INBwZb5SYq9PMIQcCG86wF7IfiIxhgnYRaKBxL2YNj916p25JUbbr3sILi9HEIXmO/K0yRpA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Lx0DaA8v; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Lx0DaA8v" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BB5311F0089A; Sun, 27 Sep 2026 06:14:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790489692; bh=DbrMloob0rMFNE1dby1PH+/b8rGYTqVadBb2Jjxo+U0=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Lx0DaA8vjH/NCMN6nES0DY+uf4nyq8hYxXblYE2y64fyVCoUNOHI/+kISIMq4F+fE c5I8qr5J5FDfQdMAr7fl7t9+t0m7VwxMSdQciZCZiYOOWOIP9GNf5o//oZVehQ3XxU WSRIriWTb2hvEAaSraNiJR/ivSY949K8OJCSOpZ7ZaPAs84Xpng0oiWzZc0MIv6oyi 54XgQmvLSsfn88Qki8lIIndkSDGaQ8guSQshC8OxMy7U2lcT2Bk9V0IEVA8PbJM6E1 iZEz0HKNl1NQaB0AE3lfnIf+HccWXjHck9IU6D7A6o328AcL8mz2tBIhS/FHti9F1P bd5RcNslCcBag== From: Allison Henderson To: netdev@vger.kernel.org, linux-rdma@vger.kernel.org, pabeni@redhat.com, edumazet@google.com, kuba@kernel.org, horms@kernel.org Cc: achender@kernel.org Subject: [PATCH net-next v7 05/12] net/rds: split connection destroy into quiesce and kref-governed free Date: Sat, 26 Sep 2026 23:14:41 -0700 Message-Id: <20260927061448.167862-6-achender@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20260927061448.167862-1-achender@kernel.org> References: <20260927061448.167862-1-achender@kernel.org> Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Sharath Srinivasan rds_conn_destroy() tears down the transport state and immediately frees the connection, along with its paths and its workqueues. This relies on the assumption (documented in the rds_conn_destroy() comments) that "no one else is referencing the connection", which "we can only ensure ... in the rmmod path". However, the callers stopped honoring that long ago. Today, connections are also destroyed on network namespace teardown (rds_tcp_kill_sock() and rds_loop_kill_conns()), and the following patches deliberately let a connection outlive the call. This leaves loose ends since references to these destroyed connections still exist. Sockets cache their connections in rs_conn, and congestion updates will walk the maps' m_conn_list. The CM callbacks and workers may also still hold the pointer. Prepare to close those holes by making the connection refcounted: - kref_init() the connection in __rds_conn_create(); the initial reference belongs to whoever is responsible for destroying the connection. - rds_conn_destroy() still quiesces synchronously exactly as before (workers cancelled, paths dropped and shut down, queued messages purged, congestion list removal), but the frees - the transport's conn_free, the path workqueues, the c_path array and the connection slab object - move to rds_conn_destroy_fini(), which runs when the last reference is dropped via rds_conn_put(). - Export rds_conn_get()/rds_conn_put(), plus an inline rds_conn_get_unless_zero() for holders that may find a connection already on its way out, for the reference holders introduced in the following patches. rds_conn_destroy() also gains a first-caller-wins guard on the new c_destroy_in_prog flag, so that a connection handed to it a second time - which the IB unload re-sweep added later in the series does - is not quiesced twice: the later caller returns at once, without quiescing anything and without waiting for the first caller to finish, which is what the re-sweep wants. With the initial reference the only one, no second call can happen yet, so the guard is inert here. With no additional reference holders yet, this only sets up the refcounting framework and is functionally equivalent to the current code (the initial reference is the only one), so every free still completes inside rds_conn_destroy(). The next two patches make a deferred free safe - the transport unload wait and the unlinking of the transport nodes ahead of the destroy - and only then do the patches that follow take references at the places that today rely on bare pointers. Based on the Oracle UEK commit "net/rds: Add krefs to struct rds_connection". Signed-off-by: Sharath Srinivasan [achender: substantial reimplementation for net-next: UEK's rds_conn_destroy_init()/_fini() split redone against upstream's rds_conn_destroy()/rds_conn_path_destroy() (no heartbeat/reap/trace infrastructure, no rds_net, single conn hash); destroy keeps its one-call external interface; holder coverage split out into follow-up patches; rewrite commit message] Assisted-by: Claude-Code:claude-fable-5 Signed-off-by: Allison Henderson --- net/rds/connection.c | 102 +++++++++++++++++++++++++++++++++++-------- net/rds/rds.h | 19 +++++++- 2 files changed, 101 insertions(+), 20 deletions(-) diff --git a/net/rds/connection.c b/net/rds/connection.c index cbc49426ba08..638e9f3140e2 100644 --- a/net/rds/connection.c +++ b/net/rds/connection.c @@ -231,6 +231,7 @@ static struct rds_connection *__rds_conn_create(struct net *net, goto out; } + kref_init(&conn->c_refcount); INIT_HLIST_NODE(&conn->c_hash_node); conn->c_laddr = *laddr; conn->c_isv6 = !ipv6_addr_v4mapped(laddr); @@ -477,9 +478,10 @@ void rds_conn_shutdown(struct rds_conn_path *cp) * Quiesce the reconnect timer before bailing * out, though. When a pending destroy did * suppress the queue, no later pass runs, and - * rds_conn_path_destroy() is about to flush - * cp_down_w and free the path: it must not - * find cp_conn_w still armed. A successor + * rds_conn_path_quiesce() is about to flush + * cp_down_w, ahead of the path's deferred + * free: it must not find cp_conn_w still + * armed. A successor * pass, when there is one, re-arms the * reconnect from its own tail. */ @@ -526,10 +528,12 @@ void rds_conn_shutdown(struct rds_conn_path *cp) conn->c_trans->conn_slots_available(conn, false); } -/* destroy a single rds_conn_path. rds_conn_destroy() iterates over - * all paths using rds_conn_path_destroy() +/* quiesce a single rds_conn_path: shut it down and tear down any + * queued messages. rds_conn_destroy() iterates over all paths using + * rds_conn_path_quiesce(); the transport state and the workqueue are + * freed later, from rds_conn_path_free(). */ -static void rds_conn_path_destroy(struct rds_conn_path *cp) +static void rds_conn_path_quiesce(struct rds_conn_path *cp) { struct rds_message *rm, *rtmp; @@ -558,6 +562,16 @@ static void rds_conn_path_destroy(struct rds_conn_path *cp) WARN_ON(delayed_work_pending(&cp->cp_recv_w)); WARN_ON(delayed_work_pending(&cp->cp_conn_w)); WARN_ON(work_pending(&cp->cp_down_w)); +} + +/* free a quiesced rds_conn_path's transport state and workqueue; runs + * from rds_conn_destroy_fini() once the last connection reference is + * dropped. + */ +static void rds_conn_path_free(struct rds_conn_path *cp) +{ + if (!cp->cp_transport_data) + return; if (cp->cp_wq != rds_wq) { destroy_workqueue(cp->cp_wq); @@ -567,16 +581,55 @@ static void rds_conn_path_destroy(struct rds_conn_path *cp) cp->cp_conn->c_trans->conn_free(cp->cp_transport_data); } +/* Free a connection. This runs from rds_conn_put() when the last + * reference is dropped, after rds_conn_destroy() has quiesced the + * connection and dropped the initial reference. + */ +static void rds_conn_destroy_fini(struct kref *kref) +{ + struct rds_connection *conn = container_of(kref, struct rds_connection, + c_refcount); + int npaths = (conn->c_trans->t_mp_capable ? RDS_MPATH_WORKERS : 1); + unsigned long flags; + int i; + + for (i = 0; i < npaths; i++) + rds_conn_path_free(&conn->c_path[i]); + + kfree(conn->c_path); + kmem_cache_free(rds_conn_slab, conn); + + spin_lock_irqsave(&rds_conn_lock, flags); + rds_conn_count--; + spin_unlock_irqrestore(&rds_conn_lock, flags); +} + +void rds_conn_get(struct rds_connection *conn) +{ + kref_get(&conn->c_refcount); +} +EXPORT_SYMBOL_GPL(rds_conn_get); + +void rds_conn_put(struct rds_connection *conn) +{ + kref_put(&conn->c_refcount, rds_conn_destroy_fini); +} +EXPORT_SYMBOL_GPL(rds_conn_put); + /* * Stop and free a connection. * - * This can only be used in very limited circumstances. It assumes that once - * the conn has been shutdown that no one else is referencing the connection. - * We can only ensure this in the rmmod path in the current code. + * Quiesces the connection synchronously (workers cancelled, transport + * connections shut down, queued messages dropped) and drops the + * initial reference. Only the first call for a connection does any + * of that: a later one finds c_destroy_in_prog already set and + * returns at once, without waiting for the first. The memory - + * including the transport's per-connection state and the path + * workqueues - is freed once the last rds_conn_put() runs, which may + * be after this returns. */ void rds_conn_destroy(struct rds_connection *conn) { - unsigned long flags; int i; struct rds_conn_path *cp; int npaths = (conn->c_trans->t_mp_capable ? RDS_MPATH_WORKERS : 1); @@ -590,11 +643,26 @@ void rds_conn_destroy(struct rds_connection *conn) * sites (which all test rds_destroy_pending() under * rcu_read_lock()) from queueing new work on the path * workqueues once we start cancelling and destroying them. + * + * Now that the transport state stays discoverable (e.g. on the + * transports' connection lists) until the final rds_conn_put(), + * a conn can be handed to rds_conn_destroy() more than once - + * the IB unload path re-sweeps its connection list until every + * connection is gone. Only the first caller proceeds; the + * unhash also happens under rds_conn_lock, so a looked-up conn + * can never be quiesced twice. (With the initial reference the + * only one, as it is at this point in the series, nothing can + * reach a second call yet; this is the contract the following + * patches rely on.) */ + spin_lock_irq(&rds_conn_lock); + if (conn->c_destroy_in_prog) { + spin_unlock_irq(&rds_conn_lock); + return; + } WRITE_ONCE(conn->c_destroy_in_prog, true); /* Ensure conn will not be scheduled for reconnect */ - spin_lock_irq(&rds_conn_lock); hlist_del_init_rcu(&conn->c_hash_node); spin_unlock_irq(&rds_conn_lock); synchronize_rcu(); @@ -602,7 +670,7 @@ void rds_conn_destroy(struct rds_connection *conn) /* shut the connection down */ for (i = 0; i < npaths; i++) { cp = &conn->c_path[i]; - rds_conn_path_destroy(cp); + rds_conn_path_quiesce(cp); BUG_ON(!list_empty(&cp->cp_retrans)); } @@ -613,12 +681,10 @@ void rds_conn_destroy(struct rds_connection *conn) */ rds_cong_remove_conn(conn); - kfree(conn->c_path); - kmem_cache_free(rds_conn_slab, conn); - - spin_lock_irqsave(&rds_conn_lock, flags); - rds_conn_count--; - spin_unlock_irqrestore(&rds_conn_lock, flags); + /* drop the initial reference; the connection is freed from + * rds_conn_destroy_fini() once every holder has dropped theirs + */ + rds_conn_put(conn); } EXPORT_SYMBOL_GPL(rds_conn_destroy); diff --git a/net/rds/rds.h b/net/rds/rds.h index d595fb78c61f..01ac6f1507b1 100644 --- a/net/rds/rds.h +++ b/net/rds/rds.h @@ -137,6 +137,12 @@ struct rds_conn_path { /* One rds_connection per RDS address pair */ struct rds_connection { struct hlist_node c_hash_node; + /* rds_conn_destroy() quiesces the connection synchronously; + * freeing it - the connection memory, the path workqueues and + * the transport's per-connection state - is deferred until the + * last reference is dropped via rds_conn_put(). + */ + struct kref c_refcount; struct in6_addr c_laddr; struct in6_addr c_faddr; int c_dev_if; /* ifindex used for this conn */ @@ -147,8 +153,10 @@ struct rds_connection { c_pad_to_32:29; int c_npaths; bool c_with_sport_idx; - /* Set once, by rds_conn_destroy(), before it cancels the path - * works; read through rds_destroy_pending(). A site that arms + /* Set once, by rds_conn_destroy() under rds_conn_lock - a + * test-and-set, so a second destroy of the same connection + * returns at once - before it cancels the path works. Read + * through rds_destroy_pending(). A site that arms * a path work must test the predicate and queue the work inside * one rcu_read_lock() section: the synchronize_rcu() that * follows the store is what keeps a queue issued after the @@ -830,6 +838,13 @@ struct rds_connection *rds_conn_create_outgoing(struct net *net, u8 tos, gfp_t gfp, int dev_if); void rds_conn_shutdown(struct rds_conn_path *cpath); void rds_conn_destroy(struct rds_connection *conn); +void rds_conn_get(struct rds_connection *conn); +void rds_conn_put(struct rds_connection *conn); +/* take a reference unless the connection is already being freed */ +static inline bool rds_conn_get_unless_zero(struct rds_connection *conn) +{ + return kref_get_unless_zero(&conn->c_refcount); +} void rds_conn_drop(struct rds_connection *conn); void rds_conn_path_drop(struct rds_conn_path *cpath, bool destroy); void rds_conn_connect_if_down(struct rds_connection *conn); -- 2.25.1