From nobody Wed Sep 3 05:54:10 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C0885ECAAA1 for ; Mon, 24 Oct 2022 12:23:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233577AbiJXMXX (ORCPT ); Mon, 24 Oct 2022 08:23:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40712 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233410AbiJXMVk (ORCPT ); Mon, 24 Oct 2022 08:21:40 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6A62D7C1EA; Mon, 24 Oct 2022 04:59:16 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id EDD8F612A4; Mon, 24 Oct 2022 11:58:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0A428C433C1; Mon, 24 Oct 2022 11:58:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666612714; bh=/11Bn+/w1g2+97iqpB5rxj+jzSQ00chxTdkDUSp8RO0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jBB9Ov2sq6oBnmzRTiHBf99SlXGClNsrtwm1O9jjfQDxnPc7B/99lMtZVhdziRy5N w3jC7UJXAoutGM3g1xzFcCdvBdti0FueP4c4wl9B7MzSCiu5NGne6yDrA+yHnmvhPh sTPsGaiXKwgyjNGvvTlrsbDQNqkjELn29+a8VIS8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Christophe Leroy , Eric Dumazet , Willy Tarreau , "David S. Miller" , Sasha Levin Subject: [PATCH 4.19 092/229] once: add DO_ONCE_SLOW() for sleepable contexts Date: Mon, 24 Oct 2022 13:30:11 +0200 Message-Id: <20221024113002.025977656@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221024112959.085534368@linuxfoundation.org> References: <20221024112959.085534368@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Eric Dumazet [ Upstream commit 62c07983bef9d3e78e71189441e1a470f0d1e653 ] Christophe Leroy reported a ~80ms latency spike happening at first TCP connect() time. This is because __inet_hash_connect() uses get_random_once() to populate a perturbation table which became quite big after commit 4c2c8f03a5ab ("tcp: increase source port perturb table to 2^16= ") get_random_once() uses DO_ONCE(), which block hard irqs for the duration of the operation. This patch adds DO_ONCE_SLOW() which uses a mutex instead of a spinlock for operations where we prefer to stay in process context. Then __inet_hash_connect() can use get_random_slow_once() to populate its perturbation table. Fixes: 4c2c8f03a5ab ("tcp: increase source port perturb table to 2^16") Fixes: 190cc82489f4 ("tcp: change source port randomizarion at connect() ti= me") Reported-by: Christophe Leroy Link: https://lore.kernel.org/netdev/CANn89iLAEYBaoYajy0Y9UmGFff5GPxDUoG-Er= VB2jDdRNQ5Tug@mail.gmail.com/T/#t Signed-off-by: Eric Dumazet Cc: Willy Tarreau Tested-by: Christophe Leroy Signed-off-by: David S. Miller Signed-off-by: Sasha Levin --- include/linux/once.h | 28 ++++++++++++++++++++++++++++ lib/once.c | 30 ++++++++++++++++++++++++++++++ net/ipv4/inet_hashtables.c | 4 ++-- 3 files changed, 60 insertions(+), 2 deletions(-) diff --git a/include/linux/once.h b/include/linux/once.h index ae6f4eb41cbe..bb58e1c3aa03 100644 --- a/include/linux/once.h +++ b/include/linux/once.h @@ -5,10 +5,18 @@ #include #include =20 +/* Helpers used from arbitrary contexts. + * Hard irqs are blocked, be cautious. + */ bool __do_once_start(bool *done, unsigned long *flags); void __do_once_done(bool *done, struct static_key_true *once_key, unsigned long *flags, struct module *mod); =20 +/* Variant for process contexts only. */ +bool __do_once_slow_start(bool *done); +void __do_once_slow_done(bool *done, struct static_key_true *once_key, + struct module *mod); + /* Call a function exactly once. The idea of DO_ONCE() is to perform * a function call such as initialization of random seeds, etc, only * once, where DO_ONCE() can live in the fast-path. After @func has @@ -52,9 +60,29 @@ void __do_once_done(bool *done, struct static_key_true *= once_key, ___ret; \ }) =20 +/* Variant of DO_ONCE() for process/sleepable contexts. */ +#define DO_ONCE_SLOW(func, ...) \ + ({ \ + bool ___ret =3D false; \ + static bool __section(".data.once") ___done =3D false; \ + static DEFINE_STATIC_KEY_TRUE(___once_key); \ + if (static_branch_unlikely(&___once_key)) { \ + ___ret =3D __do_once_slow_start(&___done); \ + if (unlikely(___ret)) { \ + func(__VA_ARGS__); \ + __do_once_slow_done(&___done, &___once_key, \ + THIS_MODULE); \ + } \ + } \ + ___ret; \ + }) + #define get_random_once(buf, nbytes) \ DO_ONCE(get_random_bytes, (buf), (nbytes)) #define get_random_once_wait(buf, nbytes) = \ DO_ONCE(get_random_bytes_wait, (buf), (nbytes)) \ =20 +#define get_random_slow_once(buf, nbytes) \ + DO_ONCE_SLOW(get_random_bytes, (buf), (nbytes)) + #endif /* _LINUX_ONCE_H */ diff --git a/lib/once.c b/lib/once.c index 59149bf3bfb4..351f66aad310 100644 --- a/lib/once.c +++ b/lib/once.c @@ -66,3 +66,33 @@ void __do_once_done(bool *done, struct static_key_true *= once_key, once_disable_jump(once_key, mod); } EXPORT_SYMBOL(__do_once_done); + +static DEFINE_MUTEX(once_mutex); + +bool __do_once_slow_start(bool *done) + __acquires(once_mutex) +{ + mutex_lock(&once_mutex); + if (*done) { + mutex_unlock(&once_mutex); + /* Keep sparse happy by restoring an even lock count on + * this mutex. In case we return here, we don't call into + * __do_once_done but return early in the DO_ONCE_SLOW() macro. + */ + __acquire(once_mutex); + return false; + } + + return true; +} +EXPORT_SYMBOL(__do_once_slow_start); + +void __do_once_slow_done(bool *done, struct static_key_true *once_key, + struct module *mod) + __releases(once_mutex) +{ + *done =3D true; + mutex_unlock(&once_mutex); + once_disable_jump(once_key, mod); +} +EXPORT_SYMBOL(__do_once_slow_done); diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c index 5295a579ec82..70070f1003a0 100644 --- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c @@ -765,8 +765,8 @@ int __inet_hash_connect(struct inet_timewait_death_row = *death_row, if (likely(remaining > 1)) remaining &=3D ~1U; =20 - net_get_random_once(table_perturb, - INET_TABLE_PERTURB_SIZE * sizeof(*table_perturb)); + get_random_slow_once(table_perturb, + INET_TABLE_PERTURB_SIZE * sizeof(*table_perturb)); index =3D port_offset & (INET_TABLE_PERTURB_SIZE - 1); =20 offset =3D READ_ONCE(table_perturb[index]) + (port_offset >> 32); --=20 2.35.1