From patchwork Thu Jun 15 18:10:02 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 13281645 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 26DB1EB64DC for ; Thu, 15 Jun 2023 18:10:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237797AbjFOSKU (ORCPT ); Thu, 15 Jun 2023 14:10:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32970 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239387AbjFOSKM (ORCPT ); Thu, 15 Jun 2023 14:10:12 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2A2792960; Thu, 15 Jun 2023 11:10:12 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 8905A6102A; Thu, 15 Jun 2023 18:10:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 586F0C433CB; Thu, 15 Jun 2023 18:10:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686852611; bh=U6h6ZVnX1R+TPZKq+FI4cbLfEjWQ4SmBj/oLpCWrvdk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=CEZlK7GCdb9WE0sL23de54xVIUpj9JSjgpgizcOcQf65VgF3Y9YHrYcfE36RoYDCO jlJ9aTzLeztjAvJXhDxv2B5P0KPrtyFgHMch9XmU0P8ntPEwAdbRZmCJSEA8QNgIl5 GHORoF4RnwMkZBg4R3XkoY/ZgR7plNGJPf/PgBmAg9ybrQJQACTyOc2Apw12Ncvzvg 60BncB3GqgSNcWwqxv0UD1+YM+7dpRCKg5ewIUK+kNz1+D/h/iittKEKVOM2hw8HvI s8tNTMRPDrAQav5j4OXBCCjIkEO1czVyUaVt7d9u1bSqj3WJS02mZcylu0xF5xAEAB KfXc6WUzD9QgQ== 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 v3 1/3] Docs/RCU/rculist_nulls: Specify type of the object in examples Date: Thu, 15 Jun 2023 18:10:02 +0000 Message-Id: <20230615181004.86850-2-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230615181004.86850-1-sj@kernel.org> References: <20230615181004.86850-1-sj@kernel.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org The type of 'obj' in example code of rculist_nulls.rst is implicit. Provide the specific type of it before the example code. Suggested-by: aul E. McKenney Link: https://lore.kernel.org/rcu/43943609-f80c-4b6a-9844-994eef800757@paulmck-laptop/ Signed-off-by: SeongJae Park --- Documentation/RCU/rculist_nulls.rst | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/Documentation/RCU/rculist_nulls.rst b/Documentation/RCU/rculist_nulls.rst index 94a8bfe9f560..4b66e2fd2fb5 100644 --- a/Documentation/RCU/rculist_nulls.rst +++ b/Documentation/RCU/rculist_nulls.rst @@ -18,7 +18,16 @@ to solve following problem. Without 'nulls', a typical RCU linked list managing objects which are allocated with SLAB_TYPESAFE_BY_RCU kmem_cache can use the following -algorithms: +algorithms. Following examples assume 'obj' is a pointer to such +objects, which is having below type. + +:: + + struct object { + struct hlist_node obj_node; + refcount_t refcnt; + unsigned int key; + }; 1) Lookup algorithm ------------------- @@ -142,6 +151,9 @@ the beginning. If the object was moved to the same chain, then the reader doesn't care: It might occasionally scan the list again without harm. +Note that using hlist_nulls means the type of 'obj_node' field of +'struct object' becomes 'struct hlist_nulls_node'. + 1) lookup algorithm ------------------- From patchwork Thu Jun 15 18:10:03 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 13281644 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 DC27EEB64DD for ; Thu, 15 Jun 2023 18:10:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238201AbjFOSKU (ORCPT ); Thu, 15 Jun 2023 14:10:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32976 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239403AbjFOSKN (ORCPT ); Thu, 15 Jun 2023 14:10:13 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B4CDD295B; Thu, 15 Jun 2023 11:10:12 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 51D8F61B53; Thu, 15 Jun 2023 18:10:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 31B7DC433CA; Thu, 15 Jun 2023 18:10:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686852611; bh=LmZp49bujap0FTIZFNAjgmpNWjLBvfyY95sutmfr3+o=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=I0z65ADiAyCKOR5m6JF1PbHdbNM4ZmghQ5OQ4yv+XKhkevdpcC/ZohV0VrPfJf9pS cpWNYWx/mCgQYAtQvH453C8EsIKCD812AlfSG06/IWxk83+ZcnkP6vOS3WKGxVXeny QQ6agvN4Mx5e05DClpoq2uACw7grNLMcKj+ubI1cVCrBOsZ/TF9hioKzc16IelEDws 1FLeKO+irNBu1zMl0dtL4Re4406jhXNOZrc6XvGx3jTOV1+KaDq3fiVoF67cYDPA+K BP9JVFHkq35qBwLCE0DRmkIdanrbxvb5oUkQubgmdnX1VrFzSXJNBbYTW7HGwNZVXQ vEcQ4o6XC8kQw== 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 v3 2/3] Docs/RCU/rculist_nulls: Fix hlist_[nulls]_head field names of 'obj' Date: Thu, 15 Jun 2023 18:10:03 +0000 Message-Id: <20230615181004.86850-3-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230615181004.86850-1-sj@kernel.org> References: <20230615181004.86850-1-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' or 'hlist_nulls_head' field named 'obj_node', but a sentence and some code snippets are wrongly calling 'obj->obj_node.next' as 'obj->obj_next', or 'obj->obj_node' as 'member'. Fix it. Signed-off-by: SeongJae Park --- Documentation/RCU/rculist_nulls.rst | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/Documentation/RCU/rculist_nulls.rst b/Documentation/RCU/rculist_nulls.rst index 4b66e2fd2fb5..a24783ebc5df 100644 --- a/Documentation/RCU/rculist_nulls.rst +++ b/Documentation/RCU/rculist_nulls.rst @@ -63,7 +63,7 @@ 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; }) && - ({ obj = hlist_entry(pos, typeof(*obj), member); 1; }); + ({ obj = hlist_entry(pos, typeof(*obj), obj_node); 1; }); pos = rcu_dereference(next)) if (obj->key == key) return obj; @@ -75,7 +75,7 @@ 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; }) && - ({ obj = hlist_entry(pos, typeof(*obj), member); 1; }); + ({ obj = hlist_entry(pos, typeof(*obj), obj_node); 1; }); pos = rcu_dereference(pos->next)) if (obj->key == key) return obj; @@ -95,7 +95,7 @@ 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 @@ -163,7 +163,7 @@ Note that using hlist_nulls means the type of 'obj_node' field of head = &table[slot]; begin: rcu_read_lock(); - hlist_nulls_for_each_entry_rcu(obj, node, head, member) { + hlist_nulls_for_each_entry_rcu(obj, node, head, obj_node) { if (obj->key == key) { if (!try_get_ref(obj)) { // might fail for free objects rcu_read_unlock(); From patchwork Thu Jun 15 18:10:04 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 13281643 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 73FD7EB64D9 for ; Thu, 15 Jun 2023 18:10:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236748AbjFOSKT (ORCPT ); Thu, 15 Jun 2023 14:10:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32984 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239424AbjFOSKO (ORCPT ); Thu, 15 Jun 2023 14:10:14 -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 87A5C295C; Thu, 15 Jun 2023 11:10:13 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 1CAFA6104D; Thu, 15 Jun 2023 18:10:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F2046C433C0; Thu, 15 Jun 2023 18:10:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686852612; bh=BGArqnN0cuqkluggRcsoV7lA0nFMtudLK2PV5oM2SLk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Dg7w2Q4eFBTgBpgKnDq/sZZYe9EfGxulIUr82J0bCnZopXm069n/34WAAy6cD1vwO dzVlmrSLFAD9Sd4IeMhdQzy/4UuFJHbwdfqYhJCzcymyt8womLR/A7PUUz0ysTA8rR oMM4HIaFoENgdA5jVNwq56H6Y4Vj6qw+ydz/xi1aL4OcVDhaozOjSqQdQTKLOekGY0 tXStzxRXsroFSKaIQLBd6aPC+ZuGJv/pK05PSu9p54+3pFkAAA6wNnzOSEd8g9wzio ARHwJ7MqtcKwaIk7vB00eLmLl2jS7UivS148GUWuxkwkfhx7+hKzgIRjo3ulzQWGGp Eml0K6jEmwbBg== 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 v3 3/3] Docs/RCU/rculist_nulls: Fix text about atomic_set_release() Date: Thu, 15 Jun 2023 18:10:04 +0000 Message-Id: <20230615181004.86850-4-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230615181004.86850-1-sj@kernel.org> References: <20230615181004.86850-1-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 a24783ebc5df..58a32dad21b8 100644 --- a/Documentation/RCU/rculist_nulls.rst +++ b/Documentation/RCU/rculist_nulls.rst @@ -138,8 +138,7 @@ 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 @@ -194,6 +193,9 @@ Note that using hlist_nulls means the type of 'obj_node' field of 2) Insert algorithm ------------------- +Same to the above one, but uses hlist_nulls_add_head_rcu() instead of +hlist_add_head_rcu(). + :: /*