From patchwork Fri Jun 16 23:36:24 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 13283382 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 6FBF0EB64D7 for ; Fri, 16 Jun 2023 23:36:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345797AbjFPXgj (ORCPT ); Fri, 16 Jun 2023 19:36:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49318 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345777AbjFPXgg (ORCPT ); Fri, 16 Jun 2023 19:36:36 -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 5D03A3AB3; Fri, 16 Jun 2023 16:36:33 -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 E69B9623C4; Fri, 16 Jun 2023 23:36:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B90E3C433C8; Fri, 16 Jun 2023 23:36:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686958592; bh=Lcfm0OdItYB2zZ/FXd8OC9BkWFuELqxJlr2ec9I0ACI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=K6iOOxAImFvfzsq3NLrXc9ruXfxNGqrgXYH/eyLxngnCVEL/jmDC9OccFZ+RLMrxa w2+woDg/eqFXS1GB2sBBnxNNxId+ZvRFFuUx7wQANr64cj/vKQjQGbMIGJxjU3alTW 0wPb8+l+ldF5OEFSQF6pkL/EcaP6utn7hcSIZyrZCcRdQ3zrywjt5hQhBoA31Tm3DZ oVG8wbkw+e5fqOXDDEc5CUFJ/XWRyipqd7UdboPEldHvjky6zBg6RfG0uWQ2xC5i9p 7/q6qsgdXlXL1k73LYccPkm3fFVF20Z76QevEhsR+2KUAsbkyFqx2KZCgrAE+2rjHQ cFj6tqhkRHuKg== 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 v4 1/3] Docs/RCU/rculist_nulls: Specify type of the object in examples Date: Fri, 16 Jun 2023 23:36:24 +0000 Message-Id: <20230616233626.83906-2-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230616233626.83906-1-sj@kernel.org> References: <20230616233626.83906-1-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: Paul 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..a6827cc31791 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; + atomic_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 Fri Jun 16 23:36:25 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 13283383 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 CC09EEB64DC for ; Fri, 16 Jun 2023 23:36:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345809AbjFPXgl (ORCPT ); Fri, 16 Jun 2023 19:36:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49334 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345789AbjFPXgj (ORCPT ); Fri, 16 Jun 2023 19:36:39 -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 4D6303AB8; Fri, 16 Jun 2023 16:36:34 -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 CA76A62F12; Fri, 16 Jun 2023 23:36:33 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 940BEC433CA; Fri, 16 Jun 2023 23:36:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686958593; bh=lBWgs+90Gck3vESACjS/SXnoZhAGTUFxSPAqJdGmdaU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ia/JrTVmfO6NJ9ySd38aUtF/rqESYfPNIJAzKeZrON1qg4fubp0SM+oq1uibr+yYp oLu7MUKEaUVTJ//Bmrkv2EyBFocI6vbRHHhG9dx9Jhs2/FgmSJC9rmUYaz83TsYZ72 zApvWG0oRnHFRPrUy8qpQieYJaSaEnvma8sxapHlng01nW7xa58jf+RpMAFtI2LYI2 Y6R8dRwPcnoTxzqn3R4RnMNAbhgqgusnSk1hVhobDOGKGwI9JEtxBDCWkpRcK+VEHD xvBgu0QmlVfOlSG/Hyb2n/VLIwUI+/KjIGZmnoMMFCQ6nz+rv70V6odz/EEW/N6irU wmXoZENqEeHDw== 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 v4 2/3] Docs/RCU/rculist_nulls: Fix hlist_[nulls]_head field names of 'obj' Date: Fri, 16 Jun 2023 23:36:25 +0000 Message-Id: <20230616233626.83906-3-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230616233626.83906-1-sj@kernel.org> References: <20230616233626.83906-1-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 a6827cc31791..4afa11f2c906 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 Fri Jun 16 23:36:26 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: SeongJae Park X-Patchwork-Id: 13283384 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 3D1D8EB64D7 for ; Fri, 16 Jun 2023 23:36:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232916AbjFPXgm (ORCPT ); Fri, 16 Jun 2023 19:36:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49388 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345821AbjFPXgj (ORCPT ); Fri, 16 Jun 2023 19:36:39 -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 129B53599; Fri, 16 Jun 2023 16:36:35 -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 9C6EF62EF0; Fri, 16 Jun 2023 23:36:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6FEB0C433D9; Fri, 16 Jun 2023 23:36:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686958594; bh=zT5gbB7rVoap1E8WJihukUSBZgfptu3BhHsTT2AdGt4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=CVdz3loJKxKxjdEMlRpBM4tKvO2y4Jrovl353vdDDH2FFxpc98MD95I/mEwiT4ob2 8wZZX+QOiS3TLDzQbAAXJqtP541njXoNd8k68OJmrjPXZEkWbV2AVsOA275Fkv+jbC Nu0CkrUx949fmWRdKZA/wrp5lVh6pEzrUFt0u6LChu1Rpxdn0pPkx5m7hxVGEYm7bK 0t1lAeWBRhZUomwU7zVRICIyyjyXXcOBdJ0H6fpjbv3BTHD8wN1/QW4l47DA66Oved vC1Y0VRlM3B5inFxlLn1/QjPRpS68s1ZPO10+fDXtibFlvvppIt8xZAWN3B9Qb2FSC if1YnUwwzSd7A== 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 v4 3/3] Docs/RCU/rculist_nulls: Fix text about atomic_set_release() Date: Fri, 16 Jun 2023 23:36:26 +0000 Message-Id: <20230616233626.83906-4-sj@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20230616233626.83906-1-sj@kernel.org> References: <20230616233626.83906-1-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 4afa11f2c906..660cc3f0f1e5 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(). + :: /*