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Message-ID: <20191101075338.GI20975@paulmck-ThinkPad-P72>
Date: Fri, 1 Nov 2019 00:53:38 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Madhuparna Bhowmik <madhuparnabhowmik04@...il.com>
Cc: Phong Tran <tranmanphong@...il.com>, 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
Subject: Re: [PATCH] Doc: convert whatisRCU.txt to rst
On Fri, Nov 01, 2019 at 09:03:57AM +0530, Madhuparna Bhowmik wrote:
> On Fri, 1 Nov, 2019, 4:24 AM Paul E. McKenney, <paulmck@...nel.org> wrote:
>
> > 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?
> >
>
> Sure, I will do it.
Thank you, Madhuparna!
Thanx, Paul
> Regards
> Madhuparna
>
>
> > 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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