Commit Graph

83 Commits

Author SHA1 Message Date
Richard Maina
7c327d5659 hwspinlock: Introduce hwspin_lock_bust()
When a remoteproc crashes or goes down unexpectedly this can result in
a state where locks held by the remoteproc will remain locked possibly
resulting in deadlock. This new API hwspin_lock_bust() allows
hwspinlock implementers to define a bust operation for freeing previously
acquired hwspinlocks after verifying ownership of the acquired lock.

Signed-off-by: Richard Maina <quic_rmaina@quicinc.com>
Reviewed-by: Bjorn Andersson <andersson@kernel.org>
Signed-off-by: Chris Lew <quic_clew@quicinc.com>
Link: https://lore.kernel.org/r/20240529-hwspinlock-bust-v3-1-c8b924ffa5a2@quicinc.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
2024-05-29 12:52:26 -07:00
Ingo Molnar
2b9d9e0a9b locking/mutex: Clarify that mutex_unlock(), and most other sleeping locks, can still use the lock object after it's unlocked
Clarify the mutex lock lifetime rules a bit more.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jann Horn <jannh@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20231201121808.GL3818@noisy.programming.kicks-ass.net
2024-01-08 09:55:31 +01:00
Jann Horn
a51749ab34 locking/mutex: Document that mutex_unlock() is non-atomic
I have seen several cases of attempts to use mutex_unlock() to release an
object such that the object can then be freed by another task.

This is not safe because mutex_unlock(), in the
MUTEX_FLAG_WAITERS && !MUTEX_FLAG_HANDOFF case, accesses the mutex
structure after having marked it as unlocked; so mutex_unlock() requires
its caller to ensure that the mutex stays alive until mutex_unlock()
returns.

If MUTEX_FLAG_WAITERS is set and there are real waiters, those waiters
have to keep the mutex alive, but we could have a spurious
MUTEX_FLAG_WAITERS left if an interruptible/killable waiter bailed
between the points where __mutex_unlock_slowpath() did the cmpxchg
reading the flags and where it acquired the wait_lock.

( With spinlocks, that kind of code pattern is allowed and, from what I
  remember, used in several places in the kernel. )

Document this, such a semantic difference between mutexes and spinlocks
is fairly unintuitive.

[ mingo: Made the changelog a bit more assertive, refined the comments. ]

Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20231130204817.2031407-1-jannh@google.com
2023-12-01 11:27:43 +01:00
Bjorn Helgaas
d56b699d76 Documentation: Fix typos
Fix typos in Documentation.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20230814212822.193684-4-helgaas@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2023-08-18 11:29:03 -06:00
Randy Dunlap
96e3cc270d Documentation: use capitalization for chapters and acronyms
Use capital letters in acronyms for CD-ROM, FPGA, and PCMCIA.

Use capital letter in the first word of chapter headings for
Locking, Timers, and "Brief tutorial on CRC computation".

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Moritz Fischer <mdf@kernel.org>
Cc: Wu Hao <hao.wu@intel.com>
Cc: Tom Rix <trix@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Xu Yilun <yilun.xu@intel.com>
Reviewed-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20230516001518.14514-1-rdunlap@infradead.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2023-05-16 12:49:31 -06:00
Lukas Bulwahn
01178ee713 docs: locking: refer to the actual existing config names
The config is actually called CONFIG_RT_MUTEXES, not CONFIG_RT_MUTEX.

The config CONFIG_LOCK_TORTURE_TEST should be connected by underscore, for
the sake of consistent referencing to configs in the kernel documentation.

Address those issues.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20230220165749.12850-1-lukas.bulwahn@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2023-02-23 12:26:00 -07:00
Akhil Raj
d2bef8e103 Remove duplicate words inside documentation
I have removed repeated `the` inside the documentation

Signed-off-by: Akhil Raj <lf32.dev@gmail.com>
Link: https://lore.kernel.org/r/20220827145359.32599-1-lf32.dev@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2022-09-27 13:21:43 -06:00
Guilherme G. Piccoli
8d6451b9a5 Documentation: Fix duplicate statement about raw_spinlock_t type
Unless it was duplicate on purpose, to emphasize that a raw_spinlock_t
is always a spinning lock regardless of PREEMPT_RT or kernel config,
it's a bit odd that this text is duplicate. So, this patch just clean
it up, keeping the consistency with the other sections of the text.

Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 919e9e6395 ("Documentation: Add lock ordering and nesting documentation")
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Link: https://lore.kernel.org/r/20220321144133.49804-1-gpiccoli@igalia.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2022-03-25 13:30:08 -06:00
Andrew Halaney
0d2be10b30 Documentation/locking/locktypes: Fix PREEMPT_RT _bh() description
With PREEMPT_RT the _bh() version of a spinlock leaves preemption
enabled, align the doc to say that instead of the opposite.

Reported-by: Leah Leshchinsky <lleshchi@redhat.com>
Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20220224212312.2601153-1-ahalaney@redhat.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2022-03-04 10:13:19 -07:00
Sebastian Andrzej Siewior
6a631c0432 Documentation/locking/locktypes: Update migrate_disable() bits.
The initial implementation of migrate_disable() for mainline was a
wrapper around preempt_disable(). RT kernels substituted this with
a real migrate disable implementation.

Later on mainline gained true migrate disable support, but the
documentation was not updated.

Update the documentation, remove the claims about migrate_disable()
mapping to preempt_disable() on non-PREEMPT_RT kernels.

Fixes: 74d862b682 ("sched: Make migrate_disable/enable() independent of RT")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211127163200.10466-2-bigeasy@linutronix.de
2021-11-30 15:40:31 +01:00
Fernando Ramos
18be03ef23 doc: drm: remove TODO entry regarding DRM_MODSET_LOCK_ALL cleanup
The previous commits do exactly what this entry in the TODO file asks
for, thus we can remove it now as it is no longer applicable.

Signed-off-by: Fernando Ramos <greenfoo@u92.eu>
Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210924064324.229457-18-greenfoo@u92.eu
2021-10-01 13:01:05 -04:00
Alexander Aring
8c7a729d09 Documentation: locking: fix references
This patch fixes file references from txt to rst file ending in
ww-mutex-design.rst and futex-requeue-pi.rst. While on it fix a spelling
issue "desgin" to "design" reported by Matthew Wilcox.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/r/20210823183143.1691344-1-aahringo@redhat.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2021-08-24 13:20:39 -06:00
Xiongwei Song
fab6216faf locking/lockdep,doc: Improve readability of the block matrix
The block condition matrix is using 'E' as the writer notation,
however, the writer reminder below the matrix is using 'W', to make
them consistent and make the matrix more readable, we'd better to use
'W' to represent writer.

Suggested-by: Waiman Long <llong@redhat.com>
Suggested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Xiongwei Song <sxwjean@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lkml.kernel.org/r/1621868745-23311-1-git-send-email-sxwjean@me.com
2021-05-31 10:14:54 +02:00
Ahmed S. Darwish
cf48647243 Documentation: seqlock: s/LOCKTYPE/LOCKNAME/g
Sequence counters with an associated write serialization lock are called
seqcount_LOCKNAME_t. Fix the documentation accordingly.

While at it, remove a paragraph that inappropriately discussed a
seqlock.h implementation detail.

Fixes: 6dd699b13d ("seqlock: seqcount_LOCKNAME_t: Standardize naming convention")
Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20201206162143.14387-2-a.darwish@linutronix.de
2020-12-09 17:08:49 +01:00
Mauro Carvalho Chehab
e3e7439dbc docs: lockdep-design: fix some warning issues
There are several warnings caused by a recent change
224ec489d3 ("lockdep/Documention: Recursive read lock detection reasoning")

Those are reported by htmldocs build:

    Documentation/locking/lockdep-design.rst:429: WARNING: Definition list ends without a blank line; unexpected unindent.
    Documentation/locking/lockdep-design.rst:452: WARNING: Block quote ends without a blank line; unexpected unindent.
    Documentation/locking/lockdep-design.rst:453: WARNING: Unexpected indentation.
    Documentation/locking/lockdep-design.rst:453: WARNING: Blank line required after table.
    Documentation/locking/lockdep-design.rst:454: WARNING: Block quote ends without a blank line; unexpected unindent.
    Documentation/locking/lockdep-design.rst:455: WARNING: Unexpected indentation.
    Documentation/locking/lockdep-design.rst:455: WARNING: Blank line required after table.
    Documentation/locking/lockdep-design.rst:456: WARNING: Block quote ends without a blank line; unexpected unindent.
    Documentation/locking/lockdep-design.rst:457: WARNING: Unexpected indentation.
    Documentation/locking/lockdep-design.rst:457: WARNING: Blank line required after table.

Besides the reported issues, there are some missing blank
lines that ended producing wrong html output, and some
literals are not properly identified.

Also, the symbols used at the irq enabled/disable table
are not displayed as expected, as they're not literals.
Also, on another table they're using a different notation.

Fixes: 224ec489d3 ("lockdep/Documention: Recursive read lock detection reasoning")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/3b9431ac5c01e38111cd59928a93e7259ab7db0f.1603791716.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2020-10-28 11:41:15 -06:00
Ahmed S. Darwish
80793c3471 seqlock: Introduce seqcount_latch_t
Latch sequence counters are a multiversion concurrency control mechanism
where the seqcount_t counter even/odd value is used to switch between
two copies of protected data. This allows the seqcount_t read path to
safely interrupt its write side critical section (e.g. from NMIs).

Initially, latch sequence counters were implemented as a single write
function above plain seqcount_t: raw_write_seqcount_latch(). The read
side was expected to use plain seqcount_t raw_read_seqcount().

A specialized latch read function, raw_read_seqcount_latch(), was later
added. It became the standardized way for latch read paths.  Due to the
dependent load, it has one read memory barrier less than the plain
seqcount_t raw_read_seqcount() API.

Only raw_write_seqcount_latch() and raw_read_seqcount_latch() should be
used with latch sequence counters. Having *unique* read and write path
APIs means that latch sequence counters are actually a data type of
their own -- just inappropriately overloading plain seqcount_t.

Introduce seqcount_latch_t. This adds type-safety and ensures that only
the correct latch-safe APIs are to be used.

Not to break bisection, let the latch APIs also accept plain seqcount_t
or seqcount_raw_spinlock_t. After converting all call sites to
seqcount_latch_t, only that new data type will be allowed.

References: 9b0fd802e8 ("seqcount: Add raw_write_seqcount_latch()")
References: 7fc26327b7 ("seqlock: Introduce raw_read_seqcount_latch()")
References: aadd6e5caa ("time/sched_clock: Use raw_read_seqcount_latch()")
Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200827114044.11173-4-a.darwish@linutronix.de
2020-09-10 11:19:28 +02:00
Boqun Feng
224ec489d3 lockdep/Documention: Recursive read lock detection reasoning
This patch add the documentation piece for the reasoning of deadlock
detection related to recursive read lock. The following sections are
added:

*	Explain what is a recursive read lock, and what deadlock cases
	they could introduce.

*	Introduce the notations for different types of dependencies, and
	the definition of strong paths.

*	Proof for a closed strong path is both sufficient and necessary
	for deadlock detections with recursive read locks involved. The
	proof could also explain why we call the path "strong"

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-3-boqun.feng@gmail.com
2020-08-26 12:42:03 +02:00
Marta Rybczynska
92b4e9f11a Documentation/locking/locktypes: Fix local_locks documentation
Fix issues with local_locks documentation:

 - fix function names, local_lock.h has local_unlock_irqrestore(), not
   local_lock_irqrestore()

 - fix mapping table, local_unlock_irqrestore() maps to
   local_irq_restore(), not _save()

Signed-off-by: Marta Rybczynska <rybczynska@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/CAApg2=SKxQ3Sqwj6TZnV-0x0cKLXFKDaPvXT4N15MPDMKq724g@mail.gmail.com
2020-08-26 12:42:02 +02:00
Linus Torvalds
dddcbc139e A handful of obvious fixes that wandered in during the merge window.
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Merge tag 'docs-5.9-2' of git://git.lwn.net/linux

Pull documentation fixes from Jonathan Corbet:
 "A handful of obvious fixes that wandered in during the merge window"

* tag 'docs-5.9-2' of git://git.lwn.net/linux:
  Documentation/locking/locktypes: fix the typo
  doc/zh_CN: resolve undefined label warning in admin-guide index
  doc/zh_CN: fix title heading markup in admin-guide cpu-load
  docs: remove the 2.6 "Upgrading I2C Drivers" guide
  docs: Correct the release date of 5.2 stable
  mailmap: Update comments for with format and more detalis
  docs: cdrom: Fix a typo and rst markup
  Doc: admin-guide: use correct legends in kernel-parameters.txt
  Documentation/features: refresh RISC-V arch support files
  documentation: coccinelle: Improve command example for make C={1,2}
  Core-api: Documentation: Replace deprecated :c:func: Usage
  Dev-tools: Documentation: Replace deprecated :c:func: Usage
  Filesystems: Documentation: Replace deprecated :c:func: Usage
  docs: trace: fix a typo
2020-08-13 13:57:45 -07:00
Huang Shijie
1edcd4675e Documentation/locking/locktypes: fix the typo
We have three categories locks, not two.

Signed-off-by: Huang Shijie <sjhuang@iluvatar.ai>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20200813060220.18199-1-sjhuang@iluvatar.ai
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2020-08-13 14:47:38 -06:00
Linus Torvalds
97d052ea3f A set of locking fixes and updates:
- Untangle the header spaghetti which causes build failures in various
     situations caused by the lockdep additions to seqcount to validate that
     the write side critical sections are non-preemptible.
 
   - The seqcount associated lock debug addons which were blocked by the
     above fallout.
 
     seqcount writers contrary to seqlock writers must be externally
     serialized, which usually happens via locking - except for strict per
     CPU seqcounts. As the lock is not part of the seqcount, lockdep cannot
     validate that the lock is held.
 
     This new debug mechanism adds the concept of associated locks.
     sequence count has now lock type variants and corresponding
     initializers which take a pointer to the associated lock used for
     writer serialization. If lockdep is enabled the pointer is stored and
     write_seqcount_begin() has a lockdep assertion to validate that the
     lock is held.
 
     Aside of the type and the initializer no other code changes are
     required at the seqcount usage sites. The rest of the seqcount API is
     unchanged and determines the type at compile time with the help of
     _Generic which is possible now that the minimal GCC version has been
     moved up.
 
     Adding this lockdep coverage unearthed a handful of seqcount bugs which
     have been addressed already independent of this.
 
     While generaly useful this comes with a Trojan Horse twist: On RT
     kernels the write side critical section can become preemtible if the
     writers are serialized by an associated lock, which leads to the well
     known reader preempts writer livelock. RT prevents this by storing the
     associated lock pointer independent of lockdep in the seqcount and
     changing the reader side to block on the lock when a reader detects
     that a writer is in the write side critical section.
 
  - Conversion of seqcount usage sites to associated types and initializers.
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Merge tag 'locking-urgent-2020-08-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking updates from Thomas Gleixner:
 "A set of locking fixes and updates:

   - Untangle the header spaghetti which causes build failures in
     various situations caused by the lockdep additions to seqcount to
     validate that the write side critical sections are non-preemptible.

   - The seqcount associated lock debug addons which were blocked by the
     above fallout.

     seqcount writers contrary to seqlock writers must be externally
     serialized, which usually happens via locking - except for strict
     per CPU seqcounts. As the lock is not part of the seqcount, lockdep
     cannot validate that the lock is held.

     This new debug mechanism adds the concept of associated locks.
     sequence count has now lock type variants and corresponding
     initializers which take a pointer to the associated lock used for
     writer serialization. If lockdep is enabled the pointer is stored
     and write_seqcount_begin() has a lockdep assertion to validate that
     the lock is held.

     Aside of the type and the initializer no other code changes are
     required at the seqcount usage sites. The rest of the seqcount API
     is unchanged and determines the type at compile time with the help
     of _Generic which is possible now that the minimal GCC version has
     been moved up.

     Adding this lockdep coverage unearthed a handful of seqcount bugs
     which have been addressed already independent of this.

     While generally useful this comes with a Trojan Horse twist: On RT
     kernels the write side critical section can become preemtible if
     the writers are serialized by an associated lock, which leads to
     the well known reader preempts writer livelock. RT prevents this by
     storing the associated lock pointer independent of lockdep in the
     seqcount and changing the reader side to block on the lock when a
     reader detects that a writer is in the write side critical section.

   - Conversion of seqcount usage sites to associated types and
     initializers"

* tag 'locking-urgent-2020-08-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (25 commits)
  locking/seqlock, headers: Untangle the spaghetti monster
  locking, arch/ia64: Reduce <asm/smp.h> header dependencies by moving XTP bits into the new <asm/xtp.h> header
  x86/headers: Remove APIC headers from <asm/smp.h>
  seqcount: More consistent seqprop names
  seqcount: Compress SEQCNT_LOCKNAME_ZERO()
  seqlock: Fold seqcount_LOCKNAME_init() definition
  seqlock: Fold seqcount_LOCKNAME_t definition
  seqlock: s/__SEQ_LOCKDEP/__SEQ_LOCK/g
  hrtimer: Use sequence counter with associated raw spinlock
  kvm/eventfd: Use sequence counter with associated spinlock
  userfaultfd: Use sequence counter with associated spinlock
  NFSv4: Use sequence counter with associated spinlock
  iocost: Use sequence counter with associated spinlock
  raid5: Use sequence counter with associated spinlock
  vfs: Use sequence counter with associated spinlock
  timekeeping: Use sequence counter with associated raw spinlock
  xfrm: policy: Use sequence counters with associated lock
  netfilter: nft_set_rbtree: Use sequence counter with associated rwlock
  netfilter: conntrack: Use sequence counter with associated spinlock
  sched: tasks: Use sequence counter with associated spinlock
  ...
2020-08-10 19:07:44 -07:00
Linus Torvalds
2324d50d05 It's been a busy cycle for documentation - hopefully the busiest for a
while to come.  Changes include:
 
  - Some new Chinese translations
 
  - Progress on the battle against double words words and non-HTTPS URLs
 
  - Some block-mq documentation
 
  - More RST conversions from Mauro.  At this point, that task is
    essentially complete, so we shouldn't see this kind of churn again for a
    while.  Unless we decide to switch to asciidoc or something...:)
 
  - Lots of typo fixes, warning fixes, and more.
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Merge tag 'docs-5.9' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "It's been a busy cycle for documentation - hopefully the busiest for a
  while to come. Changes include:

   - Some new Chinese translations

   - Progress on the battle against double words words and non-HTTPS
     URLs

   - Some block-mq documentation

   - More RST conversions from Mauro. At this point, that task is
     essentially complete, so we shouldn't see this kind of churn again
     for a while. Unless we decide to switch to asciidoc or
     something...:)

   - Lots of typo fixes, warning fixes, and more"

* tag 'docs-5.9' of git://git.lwn.net/linux: (195 commits)
  scripts/kernel-doc: optionally treat warnings as errors
  docs: ia64: correct typo
  mailmap: add entry for <alobakin@marvell.com>
  doc/zh_CN: add cpu-load Chinese version
  Documentation/admin-guide: tainted-kernels: fix spelling mistake
  MAINTAINERS: adjust kprobes.rst entry to new location
  devices.txt: document rfkill allocation
  PCI: correct flag name
  docs: filesystems: vfs: correct flag name
  docs: filesystems: vfs: correct sync_mode flag names
  docs: path-lookup: markup fixes for emphasis
  docs: path-lookup: more markup fixes
  docs: path-lookup: fix HTML entity mojibake
  CREDITS: Replace HTTP links with HTTPS ones
  docs: process: Add an example for creating a fixes tag
  doc/zh_CN: add Chinese translation prefer section
  doc/zh_CN: add clearing-warn-once Chinese version
  doc/zh_CN: add admin-guide index
  doc:it_IT: process: coding-style.rst: Correct __maybe_unused compiler label
  futex: MAINTAINERS: Re-add selftests directory
  ...
2020-08-04 22:47:54 -07:00
Linus Torvalds
9ba19ccd2d These were the main changes in this cycle:
- LKMM updates: mostly documentation changes, but also some new litmus tests for atomic ops.
 
  - KCSAN updates: the most important change is that GCC 11 now has all fixes in place
                   to support KCSAN, so GCC support can be enabled again. Also more annotations.
 
  - futex updates: minor cleanups and simplifications
 
  - seqlock updates: merge preparatory changes/cleanups for the 'associated locks' facilities.
 
  - lockdep updates:
     - simplify IRQ trace event handling
     - add various new debug checks
     - simplify header dependencies, split out <linux/lockdep_types.h>, decouple
       lockdep from other low level headers some more
     - fix NMI handling
 
  - misc cleanups and smaller fixes
 
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'locking-core-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking updates from Ingo Molnar:

 - LKMM updates: mostly documentation changes, but also some new litmus
   tests for atomic ops.

 - KCSAN updates: the most important change is that GCC 11 now has all
   fixes in place to support KCSAN, so GCC support can be enabled again.
   Also more annotations.

 - futex updates: minor cleanups and simplifications

 - seqlock updates: merge preparatory changes/cleanups for the
   'associated locks' facilities.

 - lockdep updates:
    - simplify IRQ trace event handling
    - add various new debug checks
    - simplify header dependencies, split out <linux/lockdep_types.h>,
      decouple lockdep from other low level headers some more
    - fix NMI handling

 - misc cleanups and smaller fixes

* tag 'locking-core-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (60 commits)
  kcsan: Improve IRQ state trace reporting
  lockdep: Refactor IRQ trace events fields into struct
  seqlock: lockdep assert non-preemptibility on seqcount_t write
  lockdep: Add preemption enabled/disabled assertion APIs
  seqlock: Implement raw_seqcount_begin() in terms of raw_read_seqcount()
  seqlock: Add kernel-doc for seqcount_t and seqlock_t APIs
  seqlock: Reorder seqcount_t and seqlock_t API definitions
  seqlock: seqcount_t latch: End read sections with read_seqcount_retry()
  seqlock: Properly format kernel-doc code samples
  Documentation: locking: Describe seqlock design and usage
  locking/qspinlock: Do not include atomic.h from qspinlock_types.h
  locking/atomic: Move ATOMIC_INIT into linux/types.h
  lockdep: Move list.h inclusion into lockdep.h
  locking/lockdep: Fix TRACE_IRQFLAGS vs. NMIs
  futex: Remove unused or redundant includes
  futex: Consistently use fshared as boolean
  futex: Remove needless goto's
  futex: Remove put_futex_key()
  rwsem: fix commas in initialisation
  docs: locking: Replace HTTP links with HTTPS ones
  ...
2020-08-03 14:39:35 -07:00
Ahmed S. Darwish
55f3560df9 seqlock: Extend seqcount API with associated locks
A sequence counter write side critical section must be protected by some
form of locking to serialize writers. If the serialization primitive is
not disabling preemption implicitly, preemption has to be explicitly
disabled before entering the write side critical section.

There is no built-in debugging mechanism to verify that the lock used
for writer serialization is held and preemption is disabled. Some usage
sites like dma-buf have explicit lockdep checks for the writer-side
lock, but this covers only a small portion of the sequence counter usage
in the kernel.

Add new sequence counter types which allows to associate a lock to the
sequence counter at initialization time. The seqcount API functions are
extended to provide appropriate lockdep assertions depending on the
seqcount/lock type.

For sequence counters with associated locks that do not implicitly
disable preemption, preemption protection is enforced in the sequence
counter write side functions. This removes the need to explicitly add
preempt_disable/enable() around the write side critical sections: the
write_begin/end() functions for these new sequence counter types
automatically do this.

Introduce the following seqcount types with associated locks:

     seqcount_spinlock_t
     seqcount_raw_spinlock_t
     seqcount_rwlock_t
     seqcount_mutex_t
     seqcount_ww_mutex_t

Extend the seqcount read and write functions to branch out to the
specific seqcount_LOCKTYPE_t implementation at compile-time. This avoids
kernel API explosion per each new seqcount_LOCKTYPE_t added. Add such
compile-time type detection logic into a new, internal, seqlock header.

Document the proper seqcount_LOCKTYPE_t usage, and rationale, at
Documentation/locking/seqlock.rst.

If lockdep is disabled, this lock association is compiled out and has
neither storage size nor runtime overhead.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200720155530.1173732-10-a.darwish@linutronix.de
2020-07-29 16:14:25 +02:00
Ahmed S. Darwish
0d24f65e93 Documentation: locking: Describe seqlock design and usage
Proper documentation for the design and usage of sequence counters and
sequential locks does not exist. Complete the seqlock.h documentation as
follows:

  - Divide all documentation on a seqcount_t vs. seqlock_t basis. The
    description for both mechanisms was intermingled, which is incorrect
    since the usage constrains for each type are vastly different.

  - Add an introductory paragraph describing the internal design of, and
    rationale for, sequence counters.

  - Document seqcount_t writer non-preemptibility requirement, which was
    not previously documented anywhere, and provide a clear rationale.

  - Provide template code for seqcount_t and seqlock_t initialization
    and reader/writer critical sections.

  - Recommend using seqlock_t by default. It implicitly handles the
    serialization and non-preemptibility requirements of writers.

At seqlock.h:

  - Remove references to brlocks as they've long been removed from the
    kernel.

  - Remove references to gcc-3.x since the kernel's minimum supported
    gcc version is 4.9.

References: 0f6ed63b17 ("no need to keep brlock macros anymore...")
References: 6ec4476ac8 ("Raise gcc version requirement to 4.9")
Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200720155530.1173732-2-a.darwish@linutronix.de
2020-07-29 16:14:22 +02:00
Alexander A. Klimov
482cbb6cc3 docs: locking: Replace HTTP links with HTTPS ones
Rationale:
Reduces attack surface on kernel devs opening the links for MITM
as HTTPS traffic is much harder to manipulate.

Deterministic algorithm:
For each file:
  If not .svg:
    For each line:
      If doesn't contain `\bxmlns\b`:
        For each link, `\bhttp://[^# \t\r\n]*(?:\w|/)`:
	  If neither `\bgnu\.org/license`, nor `\bmozilla\.org/MPL\b`:
            If both the HTTP and HTTPS versions
            return 200 OK and serve the same content:
              Replace HTTP with HTTPS.

Signed-off-by: Alexander A. Klimov <grandmaster@al2klimov.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200713115728.33905-1-grandmaster@al2klimov.de
2020-07-16 23:19:51 +02:00
Randy Dunlap
8b1a17c7c5 Documentation: locking: ww-mutex-design: drop duplicated word
Drop the doubled word "up".

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20200703213649.30948-3-rdunlap@infradead.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2020-07-13 09:48:31 -06:00
Randy Dunlap
7d64394b51 Documentation: locking: mutex-design: fix duplicated word
Change the phrase "at at least" to "to at least" to be more
readable.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20200703213649.30948-2-rdunlap@infradead.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2020-07-13 09:48:31 -06:00
Alexander A. Klimov
0288199e1f docs: locking: Replace HTTP links with HTTPS ones
Rationale:
Reduces attack surface on kernel devs opening the links for MITM
as HTTPS traffic is much harder to manipulate.

Deterministic algorithm:
For each file:
  If not .svg:
    For each line:
      If doesn't contain `\bxmlns\b`:
        For each link, `\bhttp://[^# \t\r\n]*(?:\w|/)`:
	  If neither `\bgnu\.org/license`, nor `\bmozilla\.org/MPL\b`:
            If both the HTTP and HTTPS versions
            return 200 OK and serve the same content:
              Replace HTTP with HTTPS.

Signed-off-by: Alexander A. Klimov <grandmaster@al2klimov.de>
Link: https://lore.kernel.org/r/20200713115728.33905-1-grandmaster@al2klimov.de
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2020-07-13 09:34:46 -06:00
Mauro Carvalho Chehab
43cb5451df docs: RCU: Convert torture.txt to ReST
- Add a SPDX header;
- Adjust document and section titles;
- Some whitespace fixes and new line breaks;
- Mark literal blocks as such;
- Add it to RCU/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-06-29 11:58:11 -07:00
Linus Torvalds
b23c4771ff A fair amount of stuff this time around, dominated by yet another massive
set from Mauro toward the completion of the RST conversion.  I *really*
 hope we are getting close to the end of this.  Meanwhile, those patches
 reach pretty far afield to update document references around the tree;
 there should be no actual code changes there.  There will be, alas, more of
 the usual trivial merge conflicts.
 
 Beyond that we have more translations, improvements to the sphinx
 scripting, a number of additions to the sysctl documentation, and lots of
 fixes.
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Merge tag 'docs-5.8' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "A fair amount of stuff this time around, dominated by yet another
  massive set from Mauro toward the completion of the RST conversion. I
  *really* hope we are getting close to the end of this. Meanwhile,
  those patches reach pretty far afield to update document references
  around the tree; there should be no actual code changes there. There
  will be, alas, more of the usual trivial merge conflicts.

  Beyond that we have more translations, improvements to the sphinx
  scripting, a number of additions to the sysctl documentation, and lots
  of fixes"

* tag 'docs-5.8' of git://git.lwn.net/linux: (130 commits)
  Documentation: fixes to the maintainer-entry-profile template
  zswap: docs/vm: Fix typo accept_threshold_percent in zswap.rst
  tracing: Fix events.rst section numbering
  docs: acpi: fix old http link and improve document format
  docs: filesystems: add info about efivars content
  Documentation: LSM: Correct the basic LSM description
  mailmap: change email for Ricardo Ribalda
  docs: sysctl/kernel: document unaligned controls
  Documentation: admin-guide: update bug-hunting.rst
  docs: sysctl/kernel: document ngroups_max
  nvdimm: fixes to maintainter-entry-profile
  Documentation/features: Correct RISC-V kprobes support entry
  Documentation/features: Refresh the arch support status files
  Revert "docs: sysctl/kernel: document ngroups_max"
  docs: move locking-specific documents to locking/
  docs: move digsig docs to the security book
  docs: move the kref doc into the core-api book
  docs: add IRQ documentation at the core-api book
  docs: debugging-via-ohci1394.txt: add it to the core-api book
  docs: fix references for ipmi.rst file
  ...
2020-06-01 15:45:27 -07:00
Thomas Gleixner
91710728d1 locking: Introduce local_lock()
preempt_disable() and local_irq_disable/save() are in principle per CPU big
kernel locks. This has several downsides:

  - The protection scope is unknown

  - Violation of protection rules is hard to detect by instrumentation

  - For PREEMPT_RT such sections, unless in low level critical code, can
    violate the preemptability constraints.

To address this PREEMPT_RT introduced the concept of local_locks which are
strictly per CPU.

The lock operations map to preempt_disable(), local_irq_disable/save() and
the enabling counterparts on non RT enabled kernels.

If lockdep is enabled local locks gain a lock map which tracks the usage
context. This will catch cases where an area is protected by
preempt_disable() but the access also happens from interrupt context. local
locks have identified quite a few such issues over the years, the most
recent example is:

  b7d5dc2107 ("random: add a spinlock_t to struct batched_entropy")

Aside of the lockdep coverage this also improves code readability as it
precisely annotates the protection scope.

PREEMPT_RT substitutes these local locks with 'sleeping' spinlocks to
protect such sections while maintaining preemtability and CPU locality.

local locks can replace:

  - preempt_enable()/disable() pairs
  - local_irq_disable/enable() pairs
  - local_irq_save/restore() pairs

They are also used to replace code which implicitly disables preemption
like:

  - get_cpu()/put_cpu()
  - get_cpu_var()/put_cpu_var()

with PREEMPT_RT friendly constructs.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200527201119.1692513-2-bigeasy@linutronix.de
2020-05-28 10:31:09 +02:00
Mauro Carvalho Chehab
95ca6d73a8 docs: move locking-specific documents to locking/
Several files under Documentation/*.txt describe some type of
locking API. Move them to locking/ subdir and add to the
locking/index.rst index file.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/dd833a10bbd0b2c1461d78913f5ec28a7e27f00b.1588345503.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2020-05-15 12:05:07 -06:00
Federico Vaga
649f9cf5f5 doc:locking: remove info about old behavior of locktorture
It is not useful to know what was the default at some point in the
past: remove the information.

Signed-off-by: Federico Vaga <federico.vaga@vaga.pv.it>
Link: https://lore.kernel.org/r/20200426211429.29133-1-federico.vaga@vaga.pv.it
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2020-05-05 09:55:58 -06:00
Randy Dunlap
51e69e6551 Documentation/locking/locktypes: Minor copy editor fixes
Minor editorial fixes:
- remove 'enabled' from PREEMPT_RT enabled kernels for consistency
- add some periods for consistency
- add "'" for possessive CPU's
- spell out interrupts

[ tglx: Picked up Paul's suggestions ]

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lkml.kernel.org/r/ac615f36-0b44-408d-aeab-d76e4241add4@infradead.org
2020-03-28 12:47:34 +01:00
Thomas Gleixner
7ecc6aa522 Documentation/locking/locktypes: Further clarifications and wordsmithing
The documentation of rw_semaphores is wrong as it claims that the non-owner
reader release is not supported by RT. That's just history biased memory
distortion.

Split the 'Owner semantics' section up and add separate sections for
semaphore and rw_semaphore to reflect reality.

Aside of that the following updates are done:

 - Add pseudo code to document the spinlock state preserving mechanism on
   PREEMPT_RT

 - Wordsmith the bitspinlock and lock nesting sections

Co-developed-by: Paul McKenney <paulmck@kernel.org>
Signed-off-by: Paul McKenney <paulmck@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lkml.kernel.org/r/87wo78y5yy.fsf@nanos.tec.linutronix.de
2020-03-28 12:47:34 +01:00
Thomas Gleixner
919e9e6395 Documentation: Add lock ordering and nesting documentation
The kernel provides a variety of locking primitives. The nesting of these
lock types and the implications of them on RT enabled kernels is nowhere
documented.

Add initial documentation.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200321113242.026561244@linutronix.de
2020-03-21 16:00:23 +01:00
SeongJae Park
4bfdebd620 docs/locking: Fix outdated section names
Commit 2e4f5382d1 ("locking/doc: Rename LOCK/UNLOCK to
ACQUIRE/RELEASE") has not appied to 'spinlock.rst'.  This commit updates
the doc for the change.

Signed-off-by: SeongJae Park <sjpark@amazon.com>
Link: https://lore.kernel.org/r/20200131205237.29535-2-sj38.park@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2020-02-05 10:21:12 -07:00
Federico Vaga
3dbbeef42b doc:locking: fix locktorture parameter description
The description was talking about two default values: I removed the
wrong one.

Signed-off-by: Federico Vaga <federico.vaga@vaga.pv.it>
Link: https://lore.kernel.org/r/20191201121941.6971-1-federico.vaga@vaga.pv.it
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2019-12-19 11:04:29 -07:00
Federico Vaga
19ad5f79f9 doc🔒 remove reference to clever use of read-write lock
Remove the clever example about read-write lock because this type of
lock is not recommended anymore (according to the very same document).
So there is no reason to teach clever things that people should not do.

Signed-off-by: Federico Vaga <federico.vaga@vaga.pv.it>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2019-09-14 01:53:27 -06:00
Mauro Carvalho Chehab
bff9e34c67 docs: fix broken doc references due to renames
Some files got renamed but probably due to some merge conflicts,
a few references still point to the old locations.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
2019-07-17 06:57:51 -03:00
Mauro Carvalho Chehab
4c68060bf6 docs: locking: add it to the main index
The locking directory is part of the Kernel API bookset. Add
it to the index file.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
2019-07-15 11:03:03 -03:00
Mauro Carvalho Chehab
387b14684f docs: locking: convert docs to ReST and rename to *.rst
Convert the locking documents to ReST and add them to the
kernel development book where it belongs.

Most of the stuff here is just to make Sphinx to properly
parse the text file, as they're already in good shape,
not requiring massive changes in order to be parsed.

The conversion is actually:
  - add blank lines and identation in order to identify paragraphs;
  - fix tables markups;
  - add some lists markups;
  - mark literal blocks;
  - adjust title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Federico Vaga <federico.vaga@vaga.pv.it>
2019-07-15 08:53:27 -03:00
Yuyang Du
1ac4ba5ed0 locking/lockdep: Add explanation to lock usage rules in lockdep design doc
The irq usage and lock dependency rules that if violated a deacklock may
happen are explained in more detail.

Signed-off-by: Yuyang Du <duyuyang@gmail.com>
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>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-17-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-06-03 11:55:48 +02:00
Yuyang Du
c01fbbc83f locking/lockdep: Add description and explanation in lockdep design doc
More words are added to lockdep design document regarding key concepts,
which should help people without lockdep experience read and understand
lockdep reports.

Signed-off-by: Yuyang Du <duyuyang@gmail.com>
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>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-3-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-06-03 11:55:34 +02:00
Geert Uytterhoeven
866d65b9d7 Documentation/locking/lockdep: Drop last two chars of sample states
Since the removal of FS_RECLAIM annotations, lockdep states contain four
characters, not six.

Fixes: e5684bbfc3 ("Documentation/locking/lockdep: Update info about states")
Fixes: d92a8cfcb3 ("locking/lockdep: Rework FS_RECLAIM annotation")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2019-03-04 12:55:18 -07:00
Linus Torvalds
01aa9d518e This is a fairly typical cycle for documentation. There's some welcome
readability improvements for the formatted output, some LICENSES updates
 including the addition of the ISC license, the removal of the unloved and
 unmaintained 00-INDEX files, the deprecated APIs document from Kees, more
 MM docs from Mike Rapoport, and the usual pile of typo fixes and
 corrections.
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Merge tag 'docs-4.20' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "This is a fairly typical cycle for documentation. There's some welcome
  readability improvements for the formatted output, some LICENSES
  updates including the addition of the ISC license, the removal of the
  unloved and unmaintained 00-INDEX files, the deprecated APIs document
  from Kees, more MM docs from Mike Rapoport, and the usual pile of typo
  fixes and corrections"

* tag 'docs-4.20' of git://git.lwn.net/linux: (41 commits)
  docs: Fix typos in histogram.rst
  docs: Introduce deprecated APIs list
  kernel-doc: fix declaration type determination
  doc: fix a typo in adding-syscalls.rst
  docs/admin-guide: memory-hotplug: remove table of contents
  doc: printk-formats: Remove bogus kobject references for device nodes
  Documentation: preempt-locking: Use better example
  dm flakey: Document "error_writes" feature
  docs/completion.txt: Fix a couple of punctuation nits
  LICENSES: Add ISC license text
  LICENSES: Add note to CDDL-1.0 license that it should not be used
  docs/core-api: memory-hotplug: add some details about locking internals
  docs/core-api: rename memory-hotplug-notifier to memory-hotplug
  docs: improve readability for people with poorer eyesight
  yama: clarify ptrace_scope=2 in Yama documentation
  docs/vm: split memory hotplug notifier description to Documentation/core-api
  docs: move memory hotplug description into admin-guide/mm
  doc: Fix acronym "FEKEK" in ecryptfs
  docs: fix some broken documentation references
  iommu: Fix passthrough option documentation
  ...
2018-10-24 18:01:11 +01:00
Andrew Murray
bccb484b9a Documentation/lockstat: Fix trivial typo
Fix incorrect line number in example output

Signed-off-by: Andrew Murray <andrew.murray@arm.com>
Cc: Jiri Kosina <trivial@kernel.org>
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: Will Deacon <will.deacon@arm.com>
Cc: linux-doc@vger.kernel.org
Link: http://lkml.kernel.org/r/1538391663-54524-1-git-send-email-andrew.murray@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-10-02 10:59:25 +02:00
Henrik Austad
a7ddcea58a Drop all 00-INDEX files from Documentation/
This is a respin with a wider audience (all that get_maintainer returned)
and I know this spams a *lot* of people. Not sure what would be the correct
way, so my apologies for ruining your inbox.

The 00-INDEX files are supposed to give a summary of all files present
in a directory, but these files are horribly out of date and their
usefulness is brought into question. Often a simple "ls" would reveal
the same information as the filenames are generally quite descriptive as
a short introduction to what the file covers (it should not surprise
anyone what Documentation/sched/sched-design-CFS.txt covers)

A few years back it was mentioned that these files were no longer really
needed, and they have since then grown further out of date, so perhaps
it is time to just throw them out.

A short status yields the following _outdated_ 00-INDEX files, first
counter is files listed in 00-INDEX but missing in the directory, last
is files present but not listed in 00-INDEX.

List of outdated 00-INDEX:
Documentation: (4/10)
Documentation/sysctl: (0/1)
Documentation/timers: (1/0)
Documentation/blockdev: (3/1)
Documentation/w1/slaves: (0/1)
Documentation/locking: (0/1)
Documentation/devicetree: (0/5)
Documentation/power: (1/1)
Documentation/powerpc: (0/5)
Documentation/arm: (1/0)
Documentation/x86: (0/9)
Documentation/x86/x86_64: (1/1)
Documentation/scsi: (4/4)
Documentation/filesystems: (2/9)
Documentation/filesystems/nfs: (0/2)
Documentation/cgroup-v1: (0/2)
Documentation/kbuild: (0/4)
Documentation/spi: (1/0)
Documentation/virtual/kvm: (1/0)
Documentation/scheduler: (0/2)
Documentation/fb: (0/1)
Documentation/block: (0/1)
Documentation/networking: (6/37)
Documentation/vm: (1/3)

Then there are 364 subdirectories in Documentation/ with several files that
are missing 00-INDEX alltogether (and another 120 with a single file and no
00-INDEX).

I don't really have an opinion to whether or not we /should/ have 00-INDEX,
but the above 00-INDEX should either be removed or be kept up to date. If
we should keep the files, I can try to keep them updated, but I rather not
if we just want to delete them anyway.

As a starting point, remove all index-files and references to 00-INDEX and
see where the discussion is going.

Signed-off-by: Henrik Austad <henrik@austad.us>
Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Just-do-it-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Paul Moore <paul@paul-moore.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Mark Brown <broonie@kernel.org>
Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: [Almost everybody else]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2018-09-09 15:08:58 -06:00
Thomas Hellstrom
08295b3b5b locking: Implement an algorithm choice for Wound-Wait mutexes
The current Wound-Wait mutex algorithm is actually not Wound-Wait but
Wait-Die. Implement also Wound-Wait as a per-ww-class choice. Wound-Wait
is, contrary to Wait-Die a preemptive algorithm and is known to generate
fewer backoffs. Testing reveals that this is true if the
number of simultaneous contending transactions is small.
As the number of simultaneous contending threads increases, Wait-Wound
becomes inferior to Wait-Die in terms of elapsed time.
Possibly due to the larger number of held locks of sleeping transactions.

Update documentation and callers.

Timings using git://people.freedesktop.org/~thomash/ww_mutex_test
tag patch-18-06-15

Each thread runs 100000 batches of lock / unlock 800 ww mutexes randomly
chosen out of 100000. Four core Intel x86_64:

Algorithm    #threads       Rollbacks  time
Wound-Wait   4              ~100       ~17s.
Wait-Die     4              ~150000    ~19s.
Wound-Wait   16             ~360000    ~109s.
Wait-Die     16             ~450000    ~82s.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Co-authored-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
2018-07-03 09:44:36 +02:00