From patchwork Tue Jun 13 18:24:31 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 13279150 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 0E509EB64DC for ; Tue, 13 Jun 2023 18:24:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239343AbjFMSYm (ORCPT ); Tue, 13 Jun 2023 14:24:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58496 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238881AbjFMSYl (ORCPT ); Tue, 13 Jun 2023 14:24:41 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B60421709; Tue, 13 Jun 2023 11:24:40 -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 CF1526340C; Tue, 13 Jun 2023 18:24:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A0319C433F2; Tue, 13 Jun 2023 18:24:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686680679; bh=Edls777YKMqINxfhwzexWbmVYJbfX6Dotujbh1uSNaI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=g8HivGphNlKC/BBPzZXi/F+QEtdGXeSaIEMGlnYZPhGe9/MX/ReZv2APD1N5QxYSY quMgGsWg1BjNQi/KfpR1o0rSbkzzU7yR8bfYVC59aGPBDmgdKMfgmyhiQwv7vABsW0 8zReTYbeOO/RRLR7mUEbeFeZ2EGmtB6+KyaiiIVT+ZSQzCGQXKPkShwB6hv1FKClY9 vg0DGwD5FPmm4ttLlXiIcVo6FCxCkeMAIhytJi1qVlDMtpYueIf2AoByOdp9qJwyPo G+Y9mRMdxeEdhXWmB72Ex7DFQXJrIj8tLkus/j7fE9i4fXyb4uISDS/g+zMjilyIII OecBzWPuCyTIA== From: SeongJae Park To: paulmck@kernel.org Cc: SeongJae Park , joel@joelfernandes.org, mmpgouride@gmail.com, corbet@lwn.net, rcu@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 1/4] Docs/RCU/rculist_nulls: Fix trivial coding style Date: Tue, 13 Jun 2023 18:24:31 +0000 Message-Id: <20230613182434.88317-2-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230613182434.88317-1-sj@kernel.org> References: <20230613182434.88317-1-sj@kernel.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Lookup example of non-hlist_nulls management is missing a semicolon, and having inconsistent indentation (one line is using single space indentation while others are using two spaces indentation). Fix the trivial issues. Signed-off-by: SeongJae Park Reviewed-by: Joel Fernandes (Google) --- Documentation/RCU/rculist_nulls.rst | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/Documentation/RCU/rculist_nulls.rst b/Documentation/RCU/rculist_nulls.rst index 9a734bf54b76..253ecd869fc2 100644 --- a/Documentation/RCU/rculist_nulls.rst +++ b/Documentation/RCU/rculist_nulls.rst @@ -26,7 +26,7 @@ algorithms: :: begin: - rcu_read_lock() + rcu_read_lock(); obj = lockless_lookup(key); if (obj) { if (!try_get_ref(obj)) // might fail for free objects @@ -68,8 +68,8 @@ And note the traditional hlist_for_each_entry_rcu() misses this smp_rmb():: pos && ({ prefetch(pos->next); 1; }) && ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; }); pos = rcu_dereference(pos->next)) - if (obj->key == key) - return obj; + if (obj->key == key) + return obj; return NULL; Quoting Corey Minyard:: From patchwork Tue Jun 13 18:24:32 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 13279151 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 EEA88EB64DA for ; Tue, 13 Jun 2023 18:25:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239278AbjFMSYn (ORCPT ); Tue, 13 Jun 2023 14:24:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58500 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239242AbjFMSYm (ORCPT ); Tue, 13 Jun 2023 14:24:42 -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 17F30E41; Tue, 13 Jun 2023 11:24:41 -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 9D23C62F59; Tue, 13 Jun 2023 18:24:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 78518C43331; Tue, 13 Jun 2023 18:24:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686680680; bh=8QtwSYO8fDJCyX3Iukfsqd/4jzpKwmY5DKHH76v+mD8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=NLe1oDvvlDNZZOS+fcGdvyQGzbtGAu6o52EhnNihiyzLUr40EX0ESaFKJ+C8VUGm7 3B2ao510PdqLceIpEBAQHFLcjZDj+ibxFG7xGS2v0dddzUw3h9BDOlOh2aekouM0Nu 8nsaioUIkdfb8YTTx0QtWEsnKUwW++YXrqthph+T0P/yjJ2eynVkbejNRgItTykowt zbA5omcQSINpvyzkw4GpVzcHGp7DyKDrdU0DHhG+EsP9vghbx5JdekUGLUkIMmTQxY CzLuNzhTNlmKdzbqMJA2pAABmPikZJ6HKDqArYJF1d8BIAl7ySLIT4H3rHAUxInWDp 9J5JMtL7eFIzQ== From: SeongJae Park To: paulmck@kernel.org Cc: SeongJae Park , joel@joelfernandes.org, mmpgouride@gmail.com, corbet@lwn.net, rcu@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 2/4] Docs/RCU/rculist_nulls: Assign 'obj' before use from the examples Date: Tue, 13 Jun 2023 18:24:32 +0000 Message-Id: <20230613182434.88317-3-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230613182434.88317-1-sj@kernel.org> References: <20230613182434.88317-1-sj@kernel.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Lookup example code snippets in rculist_nulls.rst are using 'obj' without assignment. Fix the code to assign it properly. Signed-off-by: SeongJae Park Reviewed-by: Joel Fernandes (Google) --- Documentation/RCU/rculist_nulls.rst | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/Documentation/RCU/rculist_nulls.rst b/Documentation/RCU/rculist_nulls.rst index 253ecd869fc2..94a8bfe9f560 100644 --- a/Documentation/RCU/rculist_nulls.rst +++ b/Documentation/RCU/rculist_nulls.rst @@ -54,7 +54,7 @@ but a version with an additional memory barrier (smp_rmb()) struct hlist_node *node, *next; for (pos = rcu_dereference((head)->first); pos && ({ next = pos->next; smp_rmb(); prefetch(next); 1; }) && - ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; }); + ({ obj = hlist_entry(pos, typeof(*obj), member); 1; }); pos = rcu_dereference(next)) if (obj->key == key) return obj; @@ -66,7 +66,7 @@ And note the traditional hlist_for_each_entry_rcu() misses this smp_rmb():: struct hlist_node *node; for (pos = rcu_dereference((head)->first); pos && ({ prefetch(pos->next); 1; }) && - ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; }); + ({ obj = hlist_entry(pos, typeof(*obj), member); 1; }); pos = rcu_dereference(pos->next)) if (obj->key == key) return obj; From patchwork Tue Jun 13 18:24:33 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 13279153 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 7A88CEB64D7 for ; Tue, 13 Jun 2023 18:25:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240554AbjFMSZ1 (ORCPT ); Tue, 13 Jun 2023 14:25:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58546 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239464AbjFMSYo (ORCPT ); Tue, 13 Jun 2023 14:24:44 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 09A761709; Tue, 13 Jun 2023 11:24:43 -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 6530E62F60; Tue, 13 Jun 2023 18:24:41 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4C47EC433D9; Tue, 13 Jun 2023 18:24:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686680680; bh=WK1M1XZ0REtusB+Bs/9PHEmAd7saEbfCwi8rA6lQtaw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MqD8aL5xO0CWMpkkeYW/yEn/4+ZWMtrDpJOPYc0AU818+2mltncssD4pRjLE2v/YE ul1fEqAlvphMYolgDGG9dNXMwTwv+yb6uyT1Jpv7xjDUnrbI3hMNu7NGhviBtdiQl8 eiWkvTmmoNciGcnP3TqkTDEujMewqkeFRiVq+yVsPLkHT7DCokzG9BA8GNHMjIwNH0 SE93O2hrvohcQJ499bLwlKsUGX6e/bFGvSJqT8kXNWjMJNS6rFJrrraKh+Z9noaoPD P4+JcxyVTpuuiTC4hdmAoXL9K4eJOSQt17S27ncIO6i6z1VPi/hIsT8QPEtN5H5o5c aqWzq9WFhO91g== From: SeongJae Park To: paulmck@kernel.org Cc: SeongJae Park , joel@joelfernandes.org, mmpgouride@gmail.com, corbet@lwn.net, rcu@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 3/4] Docs/RCU/rculist_nulls: Fix hlist_head field name of 'obj' Date: Tue, 13 Jun 2023 18:24:33 +0000 Message-Id: <20230613182434.88317-4-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230613182434.88317-1-sj@kernel.org> References: <20230613182434.88317-1-sj@kernel.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org The example code snippets on rculist_nulls.rst are assuming 'obj' to have the 'hlist_head' field named 'obj_node', but a sentence is wrongly mentioning 'obj->obj_node.next' as 'obj->obj_next'. Fix it. Signed-off-by: SeongJae Park Reviewed-by: Joel Fernandes (Google) --- Documentation/RCU/rculist_nulls.rst | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/Documentation/RCU/rculist_nulls.rst b/Documentation/RCU/rculist_nulls.rst index 94a8bfe9f560..5cd6f3f8810f 100644 --- a/Documentation/RCU/rculist_nulls.rst +++ b/Documentation/RCU/rculist_nulls.rst @@ -86,7 +86,7 @@ Quoting Corey Minyard:: 2) Insertion algorithm ---------------------- -We need to make sure a reader cannot read the new 'obj->obj_next' value +We need to make sure a reader cannot read the new 'obj->obj_node.next' value and previous value of 'obj->key'. Otherwise, an item could be deleted from a chain, and inserted into another chain. If new chain was empty before the move, 'next' pointer is NULL, and lockless reader can not From patchwork Tue Jun 13 18:24:34 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 13279152 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 A7B09EB64D8 for ; Tue, 13 Jun 2023 18:25:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240423AbjFMSZQ (ORCPT ); Tue, 13 Jun 2023 14:25:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58518 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239370AbjFMSYn (ORCPT ); Tue, 13 Jun 2023 14:24:43 -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 9A54DE41; Tue, 13 Jun 2023 11:24:42 -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 2F36063365; Tue, 13 Jun 2023 18:24:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 125D1C433F1; Tue, 13 Jun 2023 18:24:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686680681; bh=tKaE0feCA4Misffydrf5UR6uG+RXTeYv2hshyi6erLw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=BhJ2cluNI4psNgHorBPau3CpVT1R9LA6maOtkq4Jg7r+eOP1b9SBvIOw2gL4U1U+p sJTDHRyT0xThUGQQ3SLFPV51kBaQry3fG6EpHHmfpVx6TLUEBMwzHlrlcuav0vhQaV BtJbiA9mYF3TaUyVgC1XDtp32cQR+GRJ5jE5SXiqkHGYF9M9LCMyC1VBaVAdeE8YB6 rbd54j5/RMZflfPPq/WfFhiV2g7HBVbkOaX4veNpewafKHPPILbiiNeVGRg4OX1rSp 24wcRcOPE9R4POUba/uQafK1PW/ggSSCEq1vPrrhTKW4g84QbMBGLbMau12YYQpZpk ouVO+GoDJhOzg== From: SeongJae Park To: paulmck@kernel.org Cc: SeongJae Park , joel@joelfernandes.org, mmpgouride@gmail.com, corbet@lwn.net, rcu@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 4/4] Docs/RCU/rculist_nulls: Fix wrong text about atomic_set_release() Date: Tue, 13 Jun 2023 18:24:34 +0000 Message-Id: <20230613182434.88317-5-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230613182434.88317-1-sj@kernel.org> References: <20230613182434.88317-1-sj@kernel.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org The document says we can avoid extra _release() in insert function when hlist_nulls is used, but that's not true[1]. Drop it. [1] https://lore.kernel.org/rcu/46440869-644a-4982-b790-b71b43976c66@paulmck-laptop/ Signed-off-by: SeongJae Park --- Documentation/RCU/rculist_nulls.rst | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/Documentation/RCU/rculist_nulls.rst b/Documentation/RCU/rculist_nulls.rst index 5cd6f3f8810f..018cc100d19b 100644 --- a/Documentation/RCU/rculist_nulls.rst +++ b/Documentation/RCU/rculist_nulls.rst @@ -129,8 +129,7 @@ very very fast (before the end of RCU grace period) Avoiding extra smp_rmb() ======================== -With hlist_nulls we can avoid extra smp_rmb() in lockless_lookup() -and extra _release() in insert function. +With hlist_nulls we can avoid extra smp_rmb() in lockless_lookup(). For example, if we choose to store the slot number as the 'nulls' end-of-list marker for each slot of the hash table, we can detect @@ -182,6 +181,9 @@ scan the list again without harm. 2) Insert algorithm ------------------- +Same to the above one, but uses hlist_nulls_add_head_rcu() instead of +hlist_add_head_rcu(). + :: /*