[Linux-kernel-mentees] [PATCH] Doc: convert whatisRCU.txt to rst

Madhuparna Bhowmik madhuparnabhowmik04 at gmail.com
Fri Nov 1 03:33:57 UTC 2019


On Fri, 1 Nov, 2019, 4:24 AM Paul E. McKenney, <paulmck at kernel.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 at gmail.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.
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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