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Message-ID: <20191031225439.GD20975@paulmck-ThinkPad-P72>
Date: Thu, 31 Oct 2019 15:54:39 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Phong Tran <tranmanphong@...il.com>
Cc: josh@...htriplett.org, rostedt@...dmis.org,
mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
joel@...lfernandes.org, corbet@....net, rcu@...r.kernel.org,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-kernel-mentees@...ts.linuxfoundation.org,
skhan@...uxfoundation.org, madhuparnabhowmik04@...il.com
Subject: Re: [PATCH] Doc: convert whatisRCU.txt to rst
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 <tranmanphong@...il.com>
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
>
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