linux-toradex.git/Documentation/memory-barriers.txt, branch v4.16

doc: De-emphasize smp_read_barrier_depends

2017-12-05T19:57:53+00:00

This commit keeps only the historical and low-level discussion of
smp_read_barrier_depends().

Signed-off-by: Paul E. McKenney 
[ paulmck: Adjusted to allow for David Howells feedback on prior commit. ]

doc: READ_ONCE() now implies smp_barrier_depends()

2017-12-04T18:50:08+00:00

This commit updates an example in memory-barriers.txt to account for
the fact that READ_ONCE() now implies smp_barrier_depends().

Signed-off-by: Paul E. McKenney 
[ paulmck: Added MEMORY_BARRIER instructions from DEC Alpha from
  READ_ONCE(), per David Howells's feedback. ]

Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2017-11-13T20:38:26+00:00

Pull core locking updates from Ingo Molnar:
 "The main changes in this cycle are:

   - Another attempt at enabling cross-release lockdep dependency
     tracking (automatically part of CONFIG_PROVE_LOCKING=y), this time
     with better performance and fewer false positives. (Byungchul Park)

   - Introduce lockdep_assert_irqs_enabled()/disabled() and convert
     open-coded equivalents to lockdep variants. (Frederic Weisbecker)

   - Add down_read_killable() and use it in the VFS's iterate_dir()
     method. (Kirill Tkhai)

   - Convert remaining uses of ACCESS_ONCE() to
     READ_ONCE()/WRITE_ONCE(). Most of the conversion was Coccinelle
     driven. (Mark Rutland, Paul E. McKenney)

   - Get rid of lockless_dereference(), by strengthening Alpha atomics,
     strengthening READ_ONCE() with smp_read_barrier_depends() and thus
     being able to convert users of lockless_dereference() to
     READ_ONCE(). (Will Deacon)

   - Various micro-optimizations:

        - better PV qspinlocks (Waiman Long),
        - better x86 barriers (Michael S. Tsirkin)
        - better x86 refcounts (Kees Cook)

   - ... plus other fixes and enhancements. (Borislav Petkov, Juergen
     Gross, Miguel Bernal Marin)"

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (70 commits)
  locking/x86: Use LOCK ADD for smp_mb() instead of MFENCE
  rcu: Use lockdep to assert IRQs are disabled/enabled
  netpoll: Use lockdep to assert IRQs are disabled/enabled
  timers/posix-cpu-timers: Use lockdep to assert IRQs are disabled/enabled
  sched/clock, sched/cputime: Use lockdep to assert IRQs are disabled/enabled
  irq_work: Use lockdep to assert IRQs are disabled/enabled
  irq/timings: Use lockdep to assert IRQs are disabled/enabled
  perf/core: Use lockdep to assert IRQs are disabled/enabled
  x86: Use lockdep to assert IRQs are disabled/enabled
  smp/core: Use lockdep to assert IRQs are disabled/enabled
  timers/hrtimer: Use lockdep to assert IRQs are disabled/enabled
  timers/nohz: Use lockdep to assert IRQs are disabled/enabled
  workqueue: Use lockdep to assert IRQs are disabled/enabled
  irq/softirqs: Use lockdep to assert IRQs are disabled/enabled
  locking/lockdep: Add IRQs disabled/enabled assertion APIs: lockdep_assert_irqs_enabled()/disabled()
  locking/pvqspinlock: Implement hybrid PV queued/unfair locks
  locking/rwlocks: Fix comments
  x86/paravirt: Set up the virt_spin_lock_key after static keys get initialized
  block, locking/lockdep: Assign a lock_class per gendisk used for wait_for_completion()
  workqueue: Remove now redundant lock acquisitions wrt. workqueue flushes
  ...

locking/barriers: Kill lockless_dereference()

2017-10-24T11:17:33+00:00

lockless_dereference() is a nice idea, but it gained little traction in
kernel code since its introduction three years ago. This is partly
because it's a pain to type, but also because using READ_ONCE() instead
has worked correctly on all architectures apart from Alpha, which is a
fully supported but somewhat niche architecture these days.

Now that READ_ONCE() has been upgraded to contain an implicit
smp_read_barrier_depends() and the few callers of lockless_dereference()
have been converted, we can remove lockless_dereference() altogether.

Signed-off-by: Will Deacon 
Cc: Linus Torvalds 
Cc: Paul E. McKenney 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/1508840570-22169-5-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar

doc: Rewrite confusing statement about memory barriers

2017-10-20T18:09:32+00:00

The "Write (or store) memory barriers" bullet of the "Variety of memory
barriers" section, calls out a sequential order of stores, which is
confusing since sequential ordering is not guaranteed.

This commit therefore rewords to avoid mentioning a sequence of stores
to clarify the intent.

Cc: Paul E. McKenney 
Signed-off-by: Guilherme G. Piccoli 
Signed-off-by: Paul E. McKenney

memory-barriers.txt: Fix typo in pairing example

2017-10-20T18:09:32+00:00

In the "general barrier pairing with implicit control depdendency"
example, the last write by CPU 1 was meant to change variable x and not
y. The example would be pretty uninteresting if no CPU ever changes x
and the variable was initialized to zero.

Signed-off-by: Scott Tsai 
Signed-off-by: Paul E. McKenney

memory-barriers: Rework multicopy-atomicity section

2017-10-09T21:23:37+00:00

Signed-off-by: Alan Stern 
Signed-off-by: Paul E. McKenney

memory-barriers: Replace uses of "transitive"

2017-10-09T21:23:36+00:00

The current version of memory-barriers.txt misuses the term "transitive",
so this commit replaces it with multi-copy atomic, also adding a
definition of this term.

Reported-by: Alan Stern 
Signed-off-by: Paul E. McKenney

Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2017-09-04T18:52:29+00:00

Pull locking updates from Ingo Molnar:

 - Add 'cross-release' support to lockdep, which allows APIs like
   completions, where it's not the 'owner' who releases the lock, to be
   tracked. It's all activated automatically under
   CONFIG_PROVE_LOCKING=y.

 - Clean up (restructure) the x86 atomics op implementation to be more
   readable, in preparation of KASAN annotations. (Dmitry Vyukov)

 - Fix static keys (Paolo Bonzini)

 - Add killable versions of down_read() et al (Kirill Tkhai)

 - Rework and fix jump_label locking (Marc Zyngier, Paolo Bonzini)

 - Rework (and fix) tlb_flush_pending() barriers (Peter Zijlstra)

 - Remove smp_mb__before_spinlock() and convert its usages, introduce
   smp_mb__after_spinlock() (Peter Zijlstra)

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (56 commits)
  locking/lockdep/selftests: Fix mixed read-write ABBA tests
  sched/completion: Avoid unnecessary stack allocation for COMPLETION_INITIALIZER_ONSTACK()
  acpi/nfit: Fix COMPLETION_INITIALIZER_ONSTACK() abuse
  locking/pvqspinlock: Relax cmpxchg's to improve performance on some architectures
  smp: Avoid using two cache lines for struct call_single_data
  locking/lockdep: Untangle xhlock history save/restore from task independence
  locking/refcounts, x86/asm: Disable CONFIG_ARCH_HAS_REFCOUNT for the time being
  futex: Remove duplicated code and fix undefined behaviour
  Documentation/locking/atomic: Finish the document...
  locking/lockdep: Fix workqueue crossrelease annotation
  workqueue/lockdep: 'Fix' flush_work() annotation
  locking/lockdep/selftests: Add mixed read-write ABBA tests
  mm, locking/barriers: Clarify tlb_flush_pending() barriers
  locking/lockdep: Make CONFIG_LOCKDEP_CROSSRELEASE and CONFIG_LOCKDEP_COMPLETIONS truly non-interactive
  locking/lockdep: Explicitly initialize wq_barrier::done::map
  locking/lockdep: Rename CONFIG_LOCKDEP_COMPLETE to CONFIG_LOCKDEP_COMPLETIONS
  locking/lockdep: Reword title of LOCKDEP_CROSSRELEASE config
  locking/lockdep: Make CONFIG_LOCKDEP_CROSSRELEASE part of CONFIG_PROVE_LOCKING
  locking/refcounts, x86/asm: Implement fast refcount overflow protection
  locking/lockdep: Fix the rollback and overwrite detection logic in crossrelease
  ...

doc: Update memory-barriers.txt for read-to-write dependencies

2017-08-17T14:29:57+00:00

The memory-barriers.txt document contains an obsolete passage stating that
smp_read_barrier_depends() is required to force ordering for read-to-write
dependencies.  We now know that this is not required, even for DEC Alpha.
This commit therefore updates this passage to state that read-to-write
dependencies are respected even without smp_read_barrier_depends().

Reported-by: Lance Roy 
Signed-off-by: Paul E. McKenney 
Cc: David Howells 
Cc: Peter Zijlstra 
Cc: Jonathan Corbet 
Cc: Alan Stern 
Cc: Andrea Parri 
Cc: Jade Alglave 
Cc: Luc Maranget 
[ paulmck: Reference control-dependencies sections and use WRITE_ONCE()
  per Will Deacon.  Correctly place split-cache paragraph while there. ]
Acked-by: Will Deacon