From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D8775CA9ECE for ; Thu, 31 Oct 2019 22:54:42 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id AAE8B20873 for ; Thu, 31 Oct 2019 22:54:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="cYH+7YE3" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AAE8B20873 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linux-kernel-mentees-bounces@lists.linuxfoundation.org Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id 7D8D8D07; Thu, 31 Oct 2019 22:54:42 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 3040FB6D for ; Thu, 31 Oct 2019 22:54:41 +0000 (UTC) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 12CC1174 for ; Thu, 31 Oct 2019 22:54:40 +0000 (UTC) Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C755D20862; Thu, 31 Oct 2019 22:54:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572562479; bh=wEulxgNW/7CyH5BrsaBX7NmTPAducRV5SCNqlJg+R88=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=cYH+7YE3Iasx8gEl4lczDjFyjjIOHW/5ZO1foJkCohzE5tIwv8oKQPomcN+wqS94i OdqugzjGBt4LZnGGA5axJ+PY3NMPE8iXNfQljzpUu+EkXhrgVD4VtBDBy+4O56dRJH FGQM4MifRjf7X0SJMgurBBrEZs2m3BRsbXOcyWc4= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 8834F3520B06; Thu, 31 Oct 2019 15:54:39 -0700 (PDT) Date: Thu, 31 Oct 2019 15:54:39 -0700 From: "Paul E. McKenney" To: Phong Tran Message-ID: <20191031225439.GD20975@paulmck-ThinkPad-P72> References: <20191030233128.14997-1-tranmanphong@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20191030233128.14997-1-tranmanphong@gmail.com> User-Agent: Mutt/1.9.4 (2018-02-28) Cc: corbet@lwn.net, linux-doc@vger.kernel.org, jiangshanlai@gmail.com, josh@joshtriplett.org, rostedt@goodmis.org, linux-kernel@vger.kernel.org, rcu@vger.kernel.org, mathieu.desnoyers@efficios.com, joel@joelfernandes.org, linux-kernel-mentees@lists.linuxfoundation.org Subject: Re: [Linux-kernel-mentees] [PATCH] Doc: convert whatisRCU.txt to rst X-BeenThere: linux-kernel-mentees@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: paulmck@kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-mentees-bounces@lists.linuxfoundation.org Errors-To: linux-kernel-mentees-bounces@lists.linuxfoundation.org Message-ID: <20191031225439._Ld_YAxV71a1oc-0qJWf9I_Sjv6PCO38WQMhTQHRfWE@z> On Thu, Oct 31, 2019 at 06:31:28AM +0700, Phong Tran wrote: > Sync the format with current state of kernel documentation. > This change base on rcu-dev branch > what changed: > - Format bullet lists > - Add literal blocks > > Signed-off-by: Phong Tran Queued and pushed with updated subject line and commit log, thank you! Could you and Madhuparna please review and test each other's .rst-conversion patches? Thanx, Paul > --- > Documentation/RCU/index.rst | 1 + > .../RCU/{whatisRCU.txt => whatisRCU.rst} | 150 +++++++++++------- > 2 files changed, 90 insertions(+), 61 deletions(-) > rename Documentation/RCU/{whatisRCU.txt => whatisRCU.rst} (91%) > > diff --git a/Documentation/RCU/index.rst b/Documentation/RCU/index.rst > index 627128c230dc..b9b11481c727 100644 > --- a/Documentation/RCU/index.rst > +++ b/Documentation/RCU/index.rst > @@ -8,6 +8,7 @@ RCU concepts > :maxdepth: 3 > > arrayRCU > + whatisRCU > rcu > listRCU > NMI-RCU > diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.rst > similarity index 91% > rename from Documentation/RCU/whatisRCU.txt > rename to Documentation/RCU/whatisRCU.rst > index 58ba05c4d97f..70d0e4c21917 100644 > --- a/Documentation/RCU/whatisRCU.txt > +++ b/Documentation/RCU/whatisRCU.rst > @@ -1,15 +1,18 @@ > +.. _rcu_doc: > + > What is RCU? -- "Read, Copy, Update" > +====================================== > > Please note that the "What is RCU?" LWN series is an excellent place > to start learning about RCU: > > -1. What is RCU, Fundamentally? http://lwn.net/Articles/262464/ > -2. What is RCU? Part 2: Usage http://lwn.net/Articles/263130/ > -3. RCU part 3: the RCU API http://lwn.net/Articles/264090/ > -4. The RCU API, 2010 Edition http://lwn.net/Articles/418853/ > - 2010 Big API Table http://lwn.net/Articles/419086/ > -5. The RCU API, 2014 Edition http://lwn.net/Articles/609904/ > - 2014 Big API Table http://lwn.net/Articles/609973/ > +| 1. What is RCU, Fundamentally? http://lwn.net/Articles/262464/ > +| 2. What is RCU? Part 2: Usage http://lwn.net/Articles/263130/ > +| 3. RCU part 3: the RCU API http://lwn.net/Articles/264090/ > +| 4. The RCU API, 2010 Edition http://lwn.net/Articles/418853/ > +| 2010 Big API Table http://lwn.net/Articles/419086/ > +| 5. The RCU API, 2014 Edition http://lwn.net/Articles/609904/ > +| 2014 Big API Table http://lwn.net/Articles/609973/ > > > What is RCU? > @@ -51,6 +54,7 @@ never need this document anyway. ;-) > > > 1. RCU OVERVIEW > +---------------- > > The basic idea behind RCU is to split updates into "removal" and > "reclamation" phases. The removal phase removes references to data items > @@ -118,6 +122,7 @@ Read on to learn about how RCU's API makes this easy. > > > 2. WHAT IS RCU'S CORE API? > +--------------------------- > > The core RCU API is quite small: > > @@ -166,7 +171,7 @@ synchronize_rcu() > read-side critical sections on all CPUs have completed. > Note that synchronize_rcu() will -not- necessarily wait for > any subsequent RCU read-side critical sections to complete. > - For example, consider the following sequence of events: > + For example, consider the following sequence of events:: > > CPU 0 CPU 1 CPU 2 > ----------------- ------------------------- --------------- > @@ -248,13 +253,13 @@ rcu_dereference() > > Common coding practice uses rcu_dereference() to copy an > RCU-protected pointer to a local variable, then dereferences > - this local variable, for example as follows: > + this local variable, for example as follows:: > > p = rcu_dereference(head.next); > return p->data; > > However, in this case, one could just as easily combine these > - into one statement: > + into one statement:: > > return rcu_dereference(head.next)->data; > > @@ -267,7 +272,7 @@ rcu_dereference() > > Note that the value returned by rcu_dereference() is valid > only within the enclosing RCU read-side critical section [1]. > - For example, the following is -not- legal: > + For example, the following is -not- legal:: > > rcu_read_lock(); > p = rcu_dereference(head.next); > @@ -315,6 +320,7 @@ rcu_dereference() > > The following diagram shows how each API communicates among the > reader, updater, and reclaimer. > +:: > > > rcu_assign_pointer() > @@ -377,10 +383,12 @@ for specialized uses, but are relatively uncommon. > > > 3. WHAT ARE SOME EXAMPLE USES OF CORE RCU API? > +----------------------------------------------- > > This section shows a simple use of the core RCU API to protect a > global pointer to a dynamically allocated structure. More-typical > uses of RCU may be found in listRCU.txt, arrayRCU.txt, and NMI-RCU.txt. > +:: > > struct foo { > int a; > @@ -467,13 +475,14 @@ arrayRCU.txt, and NMI-RCU.txt. > > > 4. WHAT IF MY UPDATING THREAD CANNOT BLOCK? > +-------------------------------------------- > > In the example above, foo_update_a() blocks until a grace period elapses. > This is quite simple, but in some cases one cannot afford to wait so > long -- there might be other high-priority work to be done. > > In such cases, one uses call_rcu() rather than synchronize_rcu(). > -The call_rcu() API is as follows: > +The call_rcu() API is as follows:: > > void call_rcu(struct rcu_head * head, > void (*func)(struct rcu_head *head)); > @@ -481,7 +490,7 @@ The call_rcu() API is as follows: > This function invokes func(head) after a grace period has elapsed. > This invocation might happen from either softirq or process context, > so the function is not permitted to block. The foo struct needs to > -have an rcu_head structure added, perhaps as follows: > +have an rcu_head structure added, perhaps as follows:: > > struct foo { > int a; > @@ -490,7 +499,7 @@ have an rcu_head structure added, perhaps as follows: > struct rcu_head rcu; > }; > > -The foo_update_a() function might then be written as follows: > +The foo_update_a() function might then be written as follows:: > > /* > * Create a new struct foo that is the same as the one currently > @@ -520,7 +529,7 @@ The foo_update_a() function might then be written as follows: > call_rcu(&old_fp->rcu, foo_reclaim); > } > > -The foo_reclaim() function might appear as follows: > +The foo_reclaim() function might appear as follows:: > > void foo_reclaim(struct rcu_head *rp) > { > @@ -552,7 +561,7 @@ o Use call_rcu() -after- removing a data element from an > > If the callback for call_rcu() is not doing anything more than calling > kfree() on the structure, you can use kfree_rcu() instead of call_rcu() > -to avoid having to write your own callback: > +to avoid having to write your own callback:: > > kfree_rcu(old_fp, rcu); > > @@ -560,6 +569,7 @@ Again, see checklist.txt for additional rules governing the use of RCU. > > > 5. WHAT ARE SOME SIMPLE IMPLEMENTATIONS OF RCU? > +------------------------------------------------ > > One of the nice things about RCU is that it has extremely simple "toy" > implementations that are a good first step towards understanding the > @@ -591,7 +601,7 @@ you allow nested rcu_read_lock() calls, you can deadlock. > However, it is probably the easiest implementation to relate to, so is > a good starting point. > > -It is extremely simple: > +It is extremely simple:: > > static DEFINE_RWLOCK(rcu_gp_mutex); > > @@ -614,7 +624,7 @@ It is extremely simple: > > [You can ignore rcu_assign_pointer() and rcu_dereference() without missing > much. But here are simplified versions anyway. And whatever you do, > -don't forget about them when submitting patches making use of RCU!] > +don't forget about them when submitting patches making use of RCU!]:: > > #define rcu_assign_pointer(p, v) \ > ({ \ > @@ -659,6 +669,7 @@ This section presents a "toy" RCU implementation that is based on > on features such as hotplug CPU and the ability to run in CONFIG_PREEMPT > kernels. The definitions of rcu_dereference() and rcu_assign_pointer() > are the same as those shown in the preceding section, so they are omitted. > +:: > > void rcu_read_lock(void) { } > > @@ -707,10 +718,12 @@ Quick Quiz #3: If it is illegal to block in an RCU read-side > > > 6. ANALOGY WITH READER-WRITER LOCKING > +-------------------------------------- > > Although RCU can be used in many different ways, a very common use of > RCU is analogous to reader-writer locking. The following unified > diff shows how closely related RCU and reader-writer locking can be. > +:: > > @@ -5,5 +5,5 @@ struct el { > int data; > @@ -762,7 +775,7 @@ diff shows how closely related RCU and reader-writer locking can be. > return 0; > } > > -Or, for those who prefer a side-by-side listing: > +Or, for those who prefer a side-by-side listing:: > > 1 struct el { 1 struct el { > 2 struct list_head list; 2 struct list_head list; > @@ -774,40 +787,44 @@ Or, for those who prefer a side-by-side listing: > 8 rwlock_t listmutex; 8 spinlock_t listmutex; > 9 struct el head; 9 struct el head; > > - 1 int search(long key, int *result) 1 int search(long key, int *result) > - 2 { 2 { > - 3 struct list_head *lp; 3 struct list_head *lp; > - 4 struct el *p; 4 struct el *p; > - 5 5 > - 6 read_lock(&listmutex); 6 rcu_read_lock(); > - 7 list_for_each_entry(p, head, lp) { 7 list_for_each_entry_rcu(p, head, lp) { > - 8 if (p->key == key) { 8 if (p->key == key) { > - 9 *result = p->data; 9 *result = p->data; > -10 read_unlock(&listmutex); 10 rcu_read_unlock(); > -11 return 1; 11 return 1; > -12 } 12 } > -13 } 13 } > -14 read_unlock(&listmutex); 14 rcu_read_unlock(); > -15 return 0; 15 return 0; > -16 } 16 } > - > - 1 int delete(long key) 1 int delete(long key) > - 2 { 2 { > - 3 struct el *p; 3 struct el *p; > - 4 4 > - 5 write_lock(&listmutex); 5 spin_lock(&listmutex); > - 6 list_for_each_entry(p, head, lp) { 6 list_for_each_entry(p, head, lp) { > - 7 if (p->key == key) { 7 if (p->key == key) { > - 8 list_del(&p->list); 8 list_del_rcu(&p->list); > - 9 write_unlock(&listmutex); 9 spin_unlock(&listmutex); > - 10 synchronize_rcu(); > -10 kfree(p); 11 kfree(p); > -11 return 1; 12 return 1; > -12 } 13 } > -13 } 14 } > -14 write_unlock(&listmutex); 15 spin_unlock(&listmutex); > -15 return 0; 16 return 0; > -16 } 17 } > +:: > + > + 1 int search(long key, int *result) 1 int search(long key, int *result) > + 2 { 2 { > + 3 struct list_head *lp; 3 struct list_head *lp; > + 4 struct el *p; 4 struct el *p; > + 5 5 > + 6 read_lock(&listmutex); 6 rcu_read_lock(); > + 7 list_for_each_entry(p, head, lp) { 7 list_for_each_entry_rcu(p, head, lp) { > + 8 if (p->key == key) { 8 if (p->key == key) { > + 9 *result = p->data; 9 *result = p->data; > + 10 read_unlock(&listmutex); 10 rcu_read_unlock(); > + 11 return 1; 11 return 1; > + 12 } 12 } > + 13 } 13 } > + 14 read_unlock(&listmutex); 14 rcu_read_unlock(); > + 15 return 0; 15 return 0; > + 16 } 16 } > + > +:: > + > + 1 int delete(long key) 1 int delete(long key) > + 2 { 2 { > + 3 struct el *p; 3 struct el *p; > + 4 4 > + 5 write_lock(&listmutex); 5 spin_lock(&listmutex); > + 6 list_for_each_entry(p, head, lp) { 6 list_for_each_entry(p, head, lp) { > + 7 if (p->key == key) { 7 if (p->key == key) { > + 8 list_del(&p->list); 8 list_del_rcu(&p->list); > + 9 write_unlock(&listmutex); 9 spin_unlock(&listmutex); > + 10 synchronize_rcu(); > + 10 kfree(p); 11 kfree(p); > + 11 return 1; 12 return 1; > + 12 } 13 } > + 13 } 14 } > + 14 write_unlock(&listmutex); 15 spin_unlock(&listmutex); > + 15 return 0; 16 return 0; > + 16 } 17 } > > Either way, the differences are quite small. Read-side locking moves > to rcu_read_lock() and rcu_read_unlock, update-side locking moves from > @@ -827,13 +844,14 @@ be used in place of synchronize_rcu(). > > > 7. FULL LIST OF RCU APIs > +------------------------- > > The RCU APIs are documented in docbook-format header comments in the > Linux-kernel source code, but it helps to have a full list of the > APIs, since there does not appear to be a way to categorize them > in docbook. Here is the list, by category. > > -RCU list traversal: > +RCU list traversal:: > > list_entry_rcu > list_first_entry_rcu > @@ -854,7 +872,7 @@ RCU list traversal: > hlist_bl_first_rcu > hlist_bl_for_each_entry_rcu > > -RCU pointer/list update: > +RCU pointer/list udate:: > > rcu_assign_pointer > list_add_rcu > @@ -876,7 +894,9 @@ RCU pointer/list update: > hlist_bl_del_rcu > hlist_bl_set_first_rcu > > -RCU: Critical sections Grace period Barrier > +RCU:: > + > + Critical sections Grace period Barrier > > rcu_read_lock synchronize_net rcu_barrier > rcu_read_unlock synchronize_rcu > @@ -885,7 +905,9 @@ RCU: Critical sections Grace period Barrier > rcu_dereference_check kfree_rcu > rcu_dereference_protected > > -bh: Critical sections Grace period Barrier > +bh:: > + > + Critical sections Grace period Barrier > > rcu_read_lock_bh call_rcu rcu_barrier > rcu_read_unlock_bh synchronize_rcu > @@ -896,7 +918,9 @@ bh: Critical sections Grace period Barrier > rcu_dereference_bh_protected > rcu_read_lock_bh_held > > -sched: Critical sections Grace period Barrier > +sched:: > + > + Critical sections Grace period Barrier > > rcu_read_lock_sched call_rcu rcu_barrier > rcu_read_unlock_sched synchronize_rcu > @@ -910,7 +934,9 @@ sched: Critical sections Grace period Barrier > rcu_read_lock_sched_held > > > -SRCU: Critical sections Grace period Barrier > +SRCU:: > + > + Critical sections Grace period Barrier > > srcu_read_lock call_srcu srcu_barrier > srcu_read_unlock synchronize_srcu > @@ -918,13 +944,14 @@ SRCU: Critical sections Grace period Barrier > srcu_dereference_check > srcu_read_lock_held > > -SRCU: Initialization/cleanup > +SRCU: Initialization/cleanup:: > + > DEFINE_SRCU > DEFINE_STATIC_SRCU > init_srcu_struct > cleanup_srcu_struct > > -All: lockdep-checked RCU-protected pointer access > +All: lockdep-checked RCU-protected pointer access:: > > rcu_access_pointer > rcu_dereference_raw > @@ -976,6 +1003,7 @@ the right tool for your job. > > > 8. ANSWERS TO QUICK QUIZZES > +---------------------------- > > Quick Quiz #1: Why is this argument naive? How could a deadlock > occur when using this algorithm in a real-world Linux > -- > 2.20.1 > _______________________________________________ Linux-kernel-mentees mailing list Linux-kernel-mentees@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees