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2018-03-10locking/memory-barriers: De-emphasize smp_read_barrier_depends() some morePaul E. McKenney1-8/+18
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: Paul 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.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-02-21memory-barriers: Fix description of data dependency barriersNikolay Borisov1-1/+1
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: Nikolay Borisov <nborisov@suse.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Peter 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.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-02-21Documentation/memory-barriers.txt: Cross-reference "tools/memory-model/"Andrea Parri1-1/+5
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=2 Co-developed-by: Andrea Parri <parri.andrea@gmail.com> Co-developed-by: Akira Yokosawa <akiyks@gmail.com> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Akira Yokosawa <akiyks@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Peter 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.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-12-05doc: De-emphasize smp_read_barrier_dependsPaul E. McKenney1-2/+5
This commit keeps only the historical and low-level discussion of smp_read_barrier_depends(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Adjusted to allow for David Howells feedback on prior commit. ]
2017-12-04doc: READ_ONCE() now implies smp_barrier_depends()Paul E. McKenney1-6/+9
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@linux.vnet.ibm.com> [ paulmck: Added MEMORY_BARRIER instructions from DEC Alpha from READ_ONCE(), per David Howells's feedback. ]
2017-11-13Merge branch 'locking-core-for-linus' of ↵Linus Torvalds1-12/+0
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 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 ...
2017-10-24locking/barriers: Kill lockless_dereference()Will Deacon1-12/+0
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 <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.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-20doc: Rewrite confusing statement about memory barriersGuilherme G. Piccoli1-2/+2
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: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-10-20memory-barriers.txt: Fix typo in pairing exampleScott Tsai1-1/+1
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 <scottt@scottt.tw> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-10-09memory-barriers: Rework multicopy-atomicity sectionAlan Stern1-28/+30
Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-10-09memory-barriers: Replace uses of "transitive"Paul E. McKenney1-94/+91
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 <stern@rowland.harvard.edu> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-09-04Merge branch 'locking-core-for-linus' of ↵Linus Torvalds1-93/+8
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 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 ...
2017-08-17doc: Update memory-barriers.txt for read-to-write dependenciesPaul E. McKenney1-17/+24
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 <ldr709@gmail.com> Signed-off-by: Paul 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: Will Deacon <will.deacon@arm.com>
2017-08-10locking: Remove smp_mb__before_spinlock()Peter Zijlstra1-4/+1
Now that there are no users of smp_mb__before_spinlock() left, remove it entirely. Signed-off-by: Peter 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: Ingo Molnar <mingo@kernel.org>
2017-08-10Documentation/locking/atomic: Add documents for new atomic_t APIsPeter Zijlstra1-89/+7
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: Peter 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: Ingo Molnar <mingo@kernel.org>
2017-07-13Merge tag '4.13-fixes' of git://git.lwn.net/linuxLinus Torvalds1-3/+3
Pull documentation fixes from Jonathan Corbet: "A set of fixes for various warnings, including the one caused by the removal of kernel/rcu/srcu.c. Also correct a stray pointer in memory-barriers.txt" * tag '4.13-fixes' of git://git.lwn.net/linux: kokr/memory-barriers.txt: Fix obsolete link to atomic_ops.txt memory-barriers.txt: Fix broken link to atomic_ops.txt docs: Turn off section numbering for the input docs docs: Include uaccess docs from the right file docs: Do not include from kernel/rcu/srcu.c
2017-07-12memory-barriers.txt: Fix broken link to atomic_ops.txtSeongJae Park1-3/+3
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: SeongJae Park <sj38.park@gmail.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2017-07-03Merge tag 'docs-4.13' of git://git.lwn.net/linuxLinus Torvalds1-5/+5
Pull documentation updates from Jonathan Corbet: "There has been a fair amount of activity in the docs tree this time around. Highlights include: - Conversion of a bunch of security documentation into RST - The conversion of the remaining DocBook templates by The Amazing Mauro Machine. We can now drop the entire DocBook build chain. - The usual collection of fixes and minor updates" * tag 'docs-4.13' of git://git.lwn.net/linux: (90 commits) scripts/kernel-doc: handle DECLARE_HASHTABLE Documentation: atomic_ops.txt is core-api/atomic_ops.rst Docs: clean up some DocBook loose ends Make the main documentation title less Geocities Docs: Use kernel-figure in vidioc-g-selection.rst Docs: fix table problems in ras.rst Docs: Fix breakage with Sphinx 1.5 and upper Docs: Include the Latex "ifthen" package doc/kokr/howto: Only send regression fixes after -rc1 docs-rst: fix broken links to dynamic-debug-howto in kernel-parameters doc: Document suitability of IBM Verse for kernel development Doc: fix a markup error in coding-style.rst docs: driver-api: i2c: remove some outdated information Documentation: DMA API: fix a typo in a function name Docs: Insert missing space to separate link from text doc/ko_KR/memory-barriers: Update control-dependencies example Documentation, kbuild: fix typo "minimun" -> "minimum" docs: Fix some formatting issues in request-key.rst doc: ReSTify keys-trusted-encrypted.txt doc: ReSTify keys-request-key.txt ...
2017-06-24Documentation: atomic_ops.txt is core-api/atomic_ops.rstPalmer Dabbelt1-5/+5
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: Palmer Dabbelt <palmer@dabbelt.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2017-06-08docs: Fix typo in Documentation/memory-barriers.txtStan Drozd1-1/+1
This commit changes "architecure" to the correct spelling, "architecture". Signed-off-by: Stan Drozd <drozdziak1@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-05-11Merge tag 'docs-4.12-2' of git://git.lwn.net/linuxLinus Torvalds1-2/+2
Pull more documentation updates from Jonathan Corbet: "Connect the newly RST-formatted documentation to the rest; this had to wait until the input pull was done. There's also a few small fixes that wandered in" * tag 'docs-4.12-2' of git://git.lwn.net/linux: doc: replace FTP URL to kernel.org with HTTPS one docs: update references to the device io book Documentation: earlycon: fix Marvell Armada 3700 UART name docs-rst: add input docs at main index and use kernel-figure
2017-05-09docs: update references to the device io bookHelmut Grohne1-2/+2
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: 8a8a602fdb83 ("docs: Convert the deviceio template to RST") Signed-off-by: Helmut Grohne <h.grohne@intenta.de> Signed-off-by: SeongJae Park <sj38.park@gmail.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2017-04-12doc: Update control-dependencies section of memory-barriers.txtpierre Kuo1-1/+1
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: pierre Kuo <vichy.kuo@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-01-14doc: Update control-dependencies section of memory-barriers.txtPaul E. McKenney1-32/+38
This commit adds consistency to examples, formatting, and a couple of additional warnings. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2016-08-12locking/Documentation: Fix a typo of example resultSeongJae Park1-1/+1
An example result for data dependent write has a typo. This commit fixes the wrong typo. Signed-off-by: SeongJae Park <sj38.park@gmail.com> Signed-off-by: Paul 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.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-08-12locking/Documentation: Fix wrong section referenceSeongJae Park1-1/+1
Signed-off-by: SeongJae Park <sj38.park@gmail.com> Signed-off-by: Paul 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.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-08-12locking/Documentation: Maintain consistent blank lineSeongJae Park1-0/+1
Signed-off-by: SeongJae Park <sj38.park@gmail.com> Signed-off-by: Paul 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.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-06-17locking/Documentation: Clarify limited control-dependency scopePaul E. McKenney1-0/+41
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: Will Deacon <will.deacon@arm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Peter 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.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-28locking/Documentation: Clarify that ACQUIRE applies to loads, RELEASE ↵Will Deacon1-0/+5
applies to stores 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: Will Deacon <will.deacon@arm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Peter 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.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-28locking/Documentation: State purpose of memory-barriers.txtDavid Howells1-0/+16
There has been some confusion about the purpose of memory-barriers.txt, so this commit adds a statement of purpose. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Paul 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.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-28locking/Documentation: Add disclaimerPeter Zijlstra1-1/+17
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: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Paul 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.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-13locking/Documentation: Mention smp_cond_acquire()Davidlohr Bueso1-2/+3
... 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: Davidlohr Bueso <dbueso@suse.de> Signed-off-by: Paul 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.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-13locking/Documentation: Insert white spaces consistentlySeongJae Park1-20/+23
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: SeongJae Park <sj38.park@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: David 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: Ingo Molnar <mingo@kernel.org>
2016-04-13locking/Documentation: Fix formatting inconsistenciesSeongJae Park1-4/+4
Signed-off-by: SeongJae Park <sj38.park@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: David 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.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-04-13locking/Documentation: Add missed subsection in TOCSeongJae Park1-0/+1
A 'Virtual Machine Guests' subsection was added by this commit: 6a65d26385bf487 ("asm-generic: implement virt_xxx memory barriers") but the TOC was not updated - update it. Signed-off-by: SeongJae Park <sj38.park@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: David 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: Ingo Molnar <mingo@kernel.org>
2016-04-13locking/Documentation: Fix missed s/lock/acquire renamesSeongJae Park1-7/+7
The terms 'lock'/'unlock' were changed to 'acquire'/'release' by the following commit: 2e4f5382d12a4 ("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: David Howells <dhowells@redhat.com> Signed-off-by: SeongJae Park <sj38.park@gmail.com> Signed-off-by: Paul 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: Ingo Molnar <mingo@kernel.org>
2016-04-13locking/Documentation: Clarify relationship of barrier() to control dependenciesPaul E. McKenney1-3/+4
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: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Paul 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.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-03-14documentation: Clarify compiler store-fusion exampleSeongJae Park1-2/+2
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: SeongJae Park <sj38.park@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-14documentation: Transitivity is not cumulativityPaul E. McKenney1-1/+1
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: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-14documentation: Add alternative release-acquire outcomePaul E. McKenney1-0/+4
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: Will Deacon <will.deacon@arm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-14documentation: Distinguish between local and global transitivityPaul E. McKenney1-2/+76
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: Peter Zijlstra <peterz@infradead.org> Reported-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-14documentation: Subsequent writes ordered by rcu_dereference()Paul E. McKenney1-0/+24
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: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-14documentation: Remove obsolete reference to RCU-protected indexesPaul E. McKenney1-15/+0
Commit #1ebee8017d84 (rcu: Eliminate array-index-based RCU primitives) eliminated the primitives supporting RCU-protected array indexes, but failed to update Documentation/memory-barriers.txt accordingly. This commit therefore removes the discussion of RCU-protected array indexes. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-14documentation: Fix memory-barriers.txt section referencesPaul E. McKenney1-2/+2
This commit fixes a couple of "Compiler Barrier" section references to be "COMPILER BARRIER". This makes it easier to find the section in the usual text editors. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-14documentation: Fix control dependency and identical storesPaul E. McKenney1-3/+7
The summary of the "CONTROL DEPENDENCIES" section incorrectly states that barrier() may be used to prevent compiler reordering when more than one leg of the control-dependent "if" statement start with identical stores. This is incorrect at high optimization levels. This commit therefore updates the summary to match the detailed description. Reported by: Jianyu Zhan <nasa4836@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-01-18Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhostLinus Torvalds1-5/+23
Pull virtio barrier rework+fixes from Michael Tsirkin: "This adds a new kind of barrier, and reworks virtio and xen to use it. Plus some fixes here and there" * tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost: (44 commits) checkpatch: add virt barriers checkpatch: check for __smp outside barrier.h checkpatch.pl: add missing memory barriers virtio: make find_vqs() checkpatch.pl-friendly virtio_balloon: fix race between migration and ballooning virtio_balloon: fix race by fill and leak s390: more efficient smp barriers s390: use generic memory barriers xen/events: use virt_xxx barriers xen/io: use virt_xxx barriers xenbus: use virt_xxx barriers virtio_ring: use virt_store_mb sh: move xchg_cmpxchg to a header by itself sh: support 1 and 2 byte xchg virtio_ring: update weak barriers to use virt_xxx Revert "virtio_ring: Update weak barriers to use dma_wmb/rmb" asm-generic: implement virt_xxx memory barriers x86: define __smp_xxx xtensa: define __smp_xxx tile: define __smp_xxx ...
2016-01-12asm-generic: implement virt_xxx memory barriersMichael S. Tsirkin1-5/+23
Guests running within virtual machines might be affected by SMP effects even if the guest itself is compiled without SMP support. This is an artifact of interfacing with an SMP host while running an UP kernel. Using mandatory barriers for this use-case would be possible but is often suboptimal. In particular, virtio uses a bunch of confusing ifdefs to work around this, while xen just uses the mandatory barriers. To better handle this case, low-level virt_mb() etc macros are made available. These are implemented trivially using the low-level __smp_xxx macros, the purpose of these wrappers is to annotate those specific cases. These have the same effect as smp_mb() etc when SMP is enabled, but generate identical code for SMP and non-SMP systems. For example, virtual machine guests should use virt_mb() rather than smp_mb() when synchronizing against a (possibly SMP) host. Suggested-by: David Miller <davem@davemloft.net> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
2016-01-11Merge branch 'locking-core-for-linus' of ↵Linus Torvalds1-2/+2
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull locking updates from Ingo Molnar: "So we have a laundry list of locking subsystem changes: - continuing barrier API and code improvements - futex enhancements - atomics API improvements - pvqspinlock enhancements: in particular lock stealing and adaptive spinning - qspinlock micro-enhancements" * 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op futex: Cleanup the goto confusion in requeue_pi() futex: Remove pointless put_pi_state calls in requeue() futex: Document pi_state refcounting in requeue code futex: Rename free_pi_state() to put_pi_state() futex: Drop refcount if requeue_pi() acquired the rtmutex locking/barriers, arch: Remove ambiguous statement in the smp_store_mb() documentation lcoking/barriers, arch: Use smp barriers in smp_store_release() locking/cmpxchg, arch: Remove tas() definitions locking/pvqspinlock: Queue node adaptive spinning locking/pvqspinlock: Allow limited lock stealing locking/pvqspinlock: Collect slowpath lock statistics sched/core, locking: Document Program-Order guarantees locking, sched: Introduce smp_cond_acquire() and use it locking/pvqspinlock, x86: Optimize the PV unlock code path locking/qspinlock: Avoid redundant read of next pointer locking/qspinlock: Prefetch the next node cacheline locking/qspinlock: Use _acquire/_release() versions of cmpxchg() & xchg() atomics: Add test for atomic operations with _relaxed variants
2015-12-05Documentation/memory-barriers.txt: Fix ACCESS_ONCE thinkoChris Metcalf1-4/+4
In commit 2ecf810121c7 ("Documentation/memory-barriers.txt: Add needed ACCESS_ONCE() calls to memory-barriers.txt") the statement "Q = P" was converted to "ACCESS_ONCE(Q) = P". This should have been "Q = ACCESS_ONCE(P)". It later became "WRITE_ONCE(Q, P)". This doesn't match the following text, which is "Q = LOAD P". Change the statement to be "Q = READ_ONCE(P)". Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-04locking/barriers, arch: Remove ambiguous statement in the smp_store_mb() ↵Davidlohr Bueso1-2/+2
documentation It serves no purpose but to confuse readers, and is most likely a left over from constant memory-barriers.txt updates. I.e.: http://lists.openwall.net/linux-kernel/2006/07/15/27 Signed-off-by: Davidlohr Bueso <dave@stgolabs.net> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: <linux-arch@vger.kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Jonathan Corbet <corbet@lwn.net> 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/1445975631-17047-5-git-send-email-dave@stgolabs.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
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