The section of memory-barriers.txt that describes the dma_Xmb() barriers
has an incorrect example claiming that a wmb() is required after writing
to coherent memory in order for those writes to be visible to a device
before a subsequent MMIO access using writel() can reach the device.

In fact, this ordering guarantee is provided (at significant cost on some
architectures such as arm and power) by writel, so the wmb() is not
necessary. writel_relaxed exists for cases where this ordering is not
required.

Fix the example and update the text to make this clearer.
Reported-by: NSinan Kaya <okaya@codeaurora.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akiyks@gmail.com
Cc: boqun.feng@gmail.com
Cc: dhowells@redhat.com
Cc: j.alglave@ucl.ac.uk
Cc: linux-arch@vger.kernel.org
Cc: luc.maranget@inria.fr
Cc: npiggin@gmail.com
Cc: parri.andrea@gmail.com
Cc: stern@rowland.harvard.edu
Link: http://lkml.kernel.org/r/1526338533-6044-1-git-send-email-paulmck@linux.vnet.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

The circular-buffers.txt is already in ReST format. So, move it to the
core-api guide, where it belongs.
Signed-off-by: NMauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

The cachetlb.txt is already in ReST format. So, move it to the
core-api guide, where it belongs.
Signed-off-by: NMauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

This commit makes further changes to memory-barrier.txt to further
de-emphasize smp_read_barrier_depends(), but leaving some discussion
for historical purposes.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akiyks@gmail.com
Cc: boqun.feng@gmail.com
Cc: dhowells@redhat.com
Cc: j.alglave@ucl.ac.uk
Cc: linux-arch@vger.kernel.org
Cc: luc.maranget@inria.fr
Cc: npiggin@gmail.com
Cc: parri.andrea@gmail.com
Cc: stern@rowland.harvard.edu
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1520443660-16858-1-git-send-email-paulmck@linux.vnet.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

In the description of data dependency barriers the words 'before' is
used erroneously. Since such barrier order dependent loads one after
the other. So substitute 'before' with 'after'.
Signed-off-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akiyks@gmail.com
Cc: boqun.feng@gmail.com
Cc: dhowells@redhat.com
Cc: j.alglave@ucl.ac.uk
Cc: linux-arch@vger.kernel.org
Cc: luc.maranget@inria.fr
Cc: npiggin@gmail.com
Cc: parri.andrea@gmail.com
Cc: stern@rowland.harvard.edu
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1519169112-20593-8-git-send-email-paulmck@linux.vnet.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

A memory consistency model is now available for the Linux kernel [1],
which "can (roughly speaking) be thought of as an automated version of
memory-barriers.txt" and which is (in turn) "accompanied by extensive
documentation on its use and its design".

Inform the (occasional) reader of memory-barriers.txt of these
developments.

[1] https://marc.info/?l=linux-kernel&m=151687290114799&w=2Co-developed-by: NAndrea Parri <parri.andrea@gmail.com>
Co-developed-by: NAkira Yokosawa <akiyks@gmail.com>
Signed-off-by: NAndrea Parri <parri.andrea@gmail.com>
Signed-off-by: NAkira Yokosawa <akiyks@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: dhowells@redhat.com
Cc: j.alglave@ucl.ac.uk
Cc: linux-arch@vger.kernel.org
Cc: luc.maranget@inria.fr
Cc: nborisov@suse.com
Cc: npiggin@gmail.com
Cc: stern@rowland.harvard.edu
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1519169112-20593-7-git-send-email-paulmck@linux.vnet.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

This commit keeps only the historical and low-level discussion of
smp_read_barrier_depends().
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Adjusted to allow for David Howells feedback on prior commit. ]

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: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Added MEMORY_BARRIER instructions from DEC Alpha from
  READ_ONCE(), per David Howells's feedback. ]

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: NWill Deacon <will.deacon@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1508840570-22169-5-git-send-email-will.deacon@arm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

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 <paulmck@linux.vnet.ibm.com>
Signed-off-by: NGuilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

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: NScott Tsai <scottt@scottt.tw>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

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: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

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: NLance Roy <ldr709@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrea Parri <parri.andrea@gmail.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Luc Maranget <luc.maranget@inria.fr>
[ paulmck: Reference control-dependencies sections and use WRITE_ONCE()
  per Will Deacon.  Correctly place split-cache paragraph while there. ]
Acked-by: NWill Deacon <will.deacon@arm.com>

Now that there are no users of smp_mb__before_spinlock() left, remove
it entirely.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Since we've vastly expanded the atomic_t interface in recent years the
existing documentation is woefully out of date and people seem to get
confused a bit.

Start a new document to hopefully better explain the current state of
affairs.

The old atomic_ops.txt also covers bitmaps and a few more details so
this is not a full replacement and we'll therefore keep that document
around until such a time that we've managed to write more text to cover
its entire.

Also please, ReST people, go away.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Few obsolete links to atomic_ops.txt exist in memory-barriers.txt though
the file has moved to core-api/atomic_ops.rst.  This commit fixes the
obsolete links.
Signed-off-by: NSeongJae Park <sj38.park@gmail.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

I was reading the memory barries documentation in order to make sure the
RISC-V barries were correct, and I found a broken link to the atomic
operations documentation.
Signed-off-by: NPalmer Dabbelt <palmer@dabbelt.com>
Acked-by: NWill Deacon <will.deacon@arm.com>
Acked-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

This commit changes "architecure" to the correct spelling,
"architecture".
Signed-off-by: NStan Drozd <drozdziak1@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

While converting the deviceiobook from DocBook to RST, dangling
references were left behind. This commit updates all remaining
references to the new location. SeongJae Park improved the ko_KR
translation.

Fixes: 8a8a602f ("docs: Convert the deviceio template to RST")
Signed-off-by: NHelmut Grohne <h.grohne@intenta.de>
Signed-off-by: NSeongJae Park <sj38.park@gmail.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

In the following example, if MAX is defined to be 1, then the compiler
knows (Q % MAX) is equal to zero.  The compiler can therefore throw
away the "then" branch (and the "if"), retaining only the "else" branch.

	q = READ_ONCE(a);
	if (q % MAX) {
		WRITE_ONCE(b, 1);
		do_something();
	} else {
		WRITE_ONCE(b, 2);
		do_something_else();
	}

It is therefore necessary to modify the example like this:

        q = READ_ONCE(a);
-       WRITE_ONCE(b, 1);
+       WRITE_ONCE(b, 2);
        do_something_else();
Signed-off-by: Npierre Kuo <vichy.kuo@gmail.com>
Acked-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

This commit adds consistency to examples, formatting, and a couple of
additional warnings.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

An example result for data dependent write has a typo.  This commit
fixes the wrong typo.
Signed-off-by: NSeongJae Park <sj38.park@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dhowells@redhat.com
Cc: linux-arch@vger.kernel.org
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1470939463-31950-3-git-send-email-paulmck@linux.vnet.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Signed-off-by: NSeongJae Park <sj38.park@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dhowells@redhat.com
Cc: linux-arch@vger.kernel.org
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1470939463-31950-2-git-send-email-paulmck@linux.vnet.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Signed-off-by: NSeongJae Park <sj38.park@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dhowells@redhat.com
Cc: linux-arch@vger.kernel.org
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1470939463-31950-1-git-send-email-paulmck@linux.vnet.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Nothing in the control-dependencies section of memory-barriers.txt
says that control dependencies don't extend beyond the end of the
if-statement containing the control dependency.  Worse yet, in many
situations, they do extend beyond that if-statement.  In particular,
the compiler cannot destroy the control dependency given proper use of
READ_ONCE() and WRITE_ONCE().  However, a weakly ordered system having
a conditional-move instruction provides the control-dependency guarantee
only to code within the scope of the if-statement itself.

This commit therefore adds words and an example demonstrating this
limitation of control dependencies.
Reported-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: corbet@lwn.net
Cc: linux-arch@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Link: http://lkml.kernel.org/r/20160615230817.GA18039@linux.vnet.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

For compound atomics performing both a load and a store operation, make
it clear that _acquire and _release variants refer only to the load and
store portions of compound atomic. For example, xchg_acquire is an xchg
operation where the load takes on ACQUIRE semantics.
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: corbet@lwn.net
Cc: dave@stgolabs.net
Cc: dhowells@redhat.com
Cc: linux-doc@vger.kernel.org
Link: http://lkml.kernel.org/r/1461691328-5429-3-git-send-email-paulmck@linux.vnet.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

There has been some confusion about the purpose of memory-barriers.txt,
so this commit adds a statement of purpose.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: corbet@lwn.net
Cc: dave@stgolabs.net
Cc: linux-doc@vger.kernel.org
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1461691328-5429-2-git-send-email-paulmck@linux.vnet.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

It appears people are reading this document as a requirements list for
building hardware. This is not the intent of this document. Nor is it
particularly suited for this purpose.

The primary purpose of this document is our collective attempt to define
a set of primitives that (hopefully) allow us to write correct code on
the myriad of SMP platforms Linux supports.

Its a definite work in progress as our understanding of these platforms,
and memory ordering in general, progresses.

Nor does being mentioned in this document mean we think its a
particularly good idea; the data dependency barrier required by Alpha
being a prime example. Yes we have it, no you're insane to require it
when building new hardware.
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: corbet@lwn.net
Cc: dave@stgolabs.net
Cc: dhowells@redhat.com
Cc: linux-doc@vger.kernel.org
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1461691328-5429-1-git-send-email-paulmck@linux.vnet.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

... do this next to smp_load_acquire() when first mentioning
ACQUIRE. While this call is briefly explained and control
dependencies are mentioned later, it does not hurt the reader.
Signed-off-by: NDavidlohr Bueso <dbueso@suse.de>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bobby.prani@gmail.com
Cc: dhowells@redhat.com
Cc: dipankar@in.ibm.com
Cc: dvhart@linux.intel.com
Cc: edumazet@google.com
Cc: fweisbec@gmail.com
Cc: jiangshanlai@gmail.com
Cc: josh@joshtriplett.org
Cc: mathieu.desnoyers@efficios.com
Cc: oleg@redhat.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/1460476375-27803-7-git-send-email-paulmck@linux.vnet.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

The document uses two newlines between sections, one newline between
item and its detailed description, and two spaces between sentences.

There are a few places that used these rules inconsistently - fix them.
Signed-off-by: NSeongJae Park <sj38.park@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: NDavid Howells <dhowells@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bobby.prani@gmail.com
Cc: dipankar@in.ibm.com
Cc: dvhart@linux.intel.com
Cc: edumazet@google.com
Cc: fweisbec@gmail.com
Cc: jiangshanlai@gmail.com
Cc: josh@joshtriplett.org
Cc: mathieu.desnoyers@efficios.com
Cc: oleg@redhat.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/1460476375-27803-5-git-send-email-paulmck@linux.vnet.ibm.com
[ Fixed the changelog. ]
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Signed-off-by: NSeongJae Park <sj38.park@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: NDavid Howells <dhowells@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bobby.prani@gmail.com
Cc: dipankar@in.ibm.com
Cc: dvhart@linux.intel.com
Cc: edumazet@google.com
Cc: fweisbec@gmail.com
Cc: jiangshanlai@gmail.com
Cc: josh@joshtriplett.org
Cc: mathieu.desnoyers@efficios.com
Cc: oleg@redhat.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/1460476375-27803-4-git-send-email-paulmck@linux.vnet.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

A 'Virtual Machine Guests' subsection was added by this commit:

6a65d263 ("asm-generic: implement virt_xxx memory barriers")

but the TOC was not updated - update it.
Signed-off-by: NSeongJae Park <sj38.park@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: NDavid Howells <dhowells@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bobby.prani@gmail.com
Cc: dipankar@in.ibm.com
Cc: dvhart@linux.intel.com
Cc: edumazet@google.com
Cc: fweisbec@gmail.com
Cc: jiangshanlai@gmail.com
Cc: josh@joshtriplett.org
Cc: mathieu.desnoyers@efficios.com
Cc: oleg@redhat.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/1460476375-27803-3-git-send-email-paulmck@linux.vnet.ibm.com
[ Rewrote the changelog. ]
Signed-off-by: NIngo Molnar <mingo@kernel.org>

The terms 'lock'/'unlock' were changed to 'acquire'/'release' by the
following commit:

  2e4f5382 ("locking/doc: Rename LOCK/UNLOCK to ACQUIRE/RELEASE")

However, the commit missed to change the table of contents - fix that.

Also, the dumb rename changed the section name 'Locking functions' to an
actively misleading 'Acquiring functions' section name.

Rename it to 'Lock acquisition functions' instead.
Suggested-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NSeongJae Park <sj38.park@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bobby.prani@gmail.com
Cc: dipankar@in.ibm.com
Cc: dvhart@linux.intel.com
Cc: edumazet@google.com
Cc: fweisbec@gmail.com
Cc: jiangshanlai@gmail.com
Cc: josh@joshtriplett.org
Cc: mathieu.desnoyers@efficios.com
Cc: oleg@redhat.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/1460476375-27803-2-git-send-email-paulmck@linux.vnet.ibm.com
[ Rewrote the changelog. ]
Signed-off-by: NIngo Molnar <mingo@kernel.org>

The current documentation claims that the compiler ignores barrier(),
which is not the case.  Instead, the compiler carefully pays attention
to barrier(), but in a creative way that still manages to destroy
the control dependency.  This commit sets the story straight.
Reported-by: NMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bobby.prani@gmail.com
Cc: dhowells@redhat.com
Cc: dipankar@in.ibm.com
Cc: dvhart@linux.intel.com
Cc: edumazet@google.com
Cc: fweisbec@gmail.com
Cc: jiangshanlai@gmail.com
Cc: josh@joshtriplett.org
Cc: oleg@redhat.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/1460476375-27803-1-git-send-email-paulmck@linux.vnet.ibm.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

The compiler store-fusion example in memory-barriers.txt uses a C
comment to represent arbitrary code that does not update a given
variable.  Unfortunately, someone could reasonably interpret the
comment as instead referring to the following line of code.  This
commit therefore replaces the comment with a string that more
clearly represents the arbitrary code.
Signed-off-by: NSeongJae Park <sj38.park@gmail.com>
Acked-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

The "transitivity" section mentions cumulativity in a potentially
confusing way.  Contrary to the current wording, cumulativity is
not transitivity, but rather a hardware discipline that can be used
to implement transitivity on ARM and PowerPC CPUs.  This commit
therefore deletes the mention of cumulativity.
Reported-by: NLuc Maranget <luc.maranget@inria.fr>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

The memory-barriers.txt discussion of local transitivity and
release-acquire chains leaves out discussion of the outcome of
the read from "u".  This commit therefore adds an outcome showing
that you can get a "1" from this read even if the release-acquire
pairs don't line up.
Reported-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

The introduction of smp_load_acquire() and smp_store_release() had
the side effect of introducing a weaker notion of transitivity:
The transitivity of full smp_mb() barriers is global, but that
of smp_store_release()/smp_load_acquire() chains is local.  This
commit therefore introduces the notion of local transitivity and
gives an example.
Reported-by: NPeter Zijlstra <peterz@infradead.org>
Reported-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

The current memory-barriers.txt does not address the possibility of
a write to a dereferenced pointer.  This should be rare, but when it
happens, we need that write -not- to be clobbered by the initialization.
This commit therefore adds an example showing a data dependency ordering
a later data-dependent write.
Reported-by: NLeonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>