kernel/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst, branch linux-rolling-stable

rcu: Update stray documentation references to rcu_dynticks_eqs_{enter, exit}()

2024-08-15T16:00:43Z

rcu_dynticks_eqs_{enter, exit}() have been replaced by their context-tracking counterparts since commit: 171476775d32 ("context_tracking: Convert state to atomic_t") Update the stray documentation references. Signed-off-by: Valentin Schneider Reviewed-by: Frederic Weisbecker Signed-off-by: Neeraj Upadhyay

rcu: Rename rcu_dynticks_in_eqs_since() into rcu_watching_snap_stopped_since()

2024-08-15T16:00:42Z

The context_tracking.state RCU_DYNTICKS subvariable has been renamed to RCU_WATCHING, the dynticks prefix can go. While at it, this helper is only meant to be called after failing an earlier call to rcu_watching_snap_in_eqs(), document this in the comments and add a WARN_ON_ONCE() for good measure. Signed-off-by: Valentin Schneider Reviewed-by: Frederic Weisbecker Signed-off-by: Neeraj Upadhyay

context_tracking, rcu: Rename ct_dynticks_cpu_acquire() into ct_rcu_watching_cpu_acquire()

2024-07-29T02:03:10Z

The context_tracking.state RCU_DYNTICKS subvariable has been renamed to RCU_WATCHING, reflect that change in the related helpers. Signed-off-by: Valentin Schneider Reviewed-by: Frederic Weisbecker Signed-off-by: Neeraj Upadhyay

rcu: Remove superfluous full memory barrier upon first EQS snapshot

2024-06-28T13:43:34Z

When the grace period kthread checks the extended quiescent state counter of a CPU, full ordering is necessary to ensure that either: * If the GP kthread observes the remote target in an extended quiescent state, then that target must observe all accesses prior to the current grace period, including the current grace period sequence number, once it exits that extended quiescent state. or: * If the GP kthread observes the remote target NOT in an extended quiescent state, then the target further entering in an extended quiescent state must observe all accesses prior to the current grace period, including the current grace period sequence number, once it enters that extended quiescent state. This ordering is enforced through a full memory barrier placed right before taking the first EQS snapshot. However this is superfluous because the snapshot is taken while holding the target's rnp lock which provides the necessary ordering through its chain of smp_mb__after_unlock_lock(). Remove the needless explicit barrier before the snapshot and put a comment about the implicit barrier newly relied upon here. Signed-off-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney Reviewed-by: Boqun Feng Reviewed-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney

Documentation: RCU: Correct spelling

2023-04-05T13:47:18Z

Correct spelling problems for Documentation/RCU/ as reported by codespell. Note: in RTFP.txt, there are other misspellings that are left as is since they were used that way in email Subject: lines or in LWN.net articles. [preemptable, Preemptable, synchonisation] Acked-by: Joel Fernandes (Google) Signed-off-by: Randy Dunlap Cc: Jonathan Corbet Cc: linux-doc@vger.kernel.org Cc: "Paul E. McKenney" Cc: Frederic Weisbecker Cc: Neeraj Upadhyay Cc: Josh Triplett Cc: rcu@vger.kernel.org Signed-off-by: Paul E. McKenney Signed-off-by: Joel Fernandes (Google)

rcu: Fix undefined Kconfig macros

2021-09-13T23:32:46Z

Invoking scripts/checkkconfigsymbols.py in the Linux-kernel source tree located the following issues: 1. TREE_PREEMPT_RCU Referencing files: arch/sh/configs/sdk7786_defconfig It should now be CONFIG_PREEMPT_RCU. Except that the CONFIG_PREEMPT=y in that same file implies CONFIG_PREEMPT_RCU=y. Therefore, delete the CONFIG_TREE_PREEMPT_RCU=y line. The reason is as follows: In kernel/rcu/Kconfig, we have config PREEMPT_RCU bool default y if PREEMPTION https://www.kernel.org/doc/Documentation/kbuild/kconfig-language.txt says, "The default value is only assigned to the config symbol if no other value was set by the user (via the input prompt above)." there is no prompt in config PREEMPT_RCU entry, so we are guaranteed to get CONFIG_PREEMPT_RCU=y when CONFIG_PREEMPT is present. 2. RCU_CPU_STALL_INFO Referencing files: arch/xtensa/configs/nommu_kc705_defconfig The old Kconfig option RCU_CPU_STALL_INFO was removed by commit 75c27f119b64 ("rcu: Remove CONFIG_RCU_CPU_STALL_INFO"), and the kernel now acts as if this Kconfig option was unconditionally enabled. 3. RCU_NOCB_CPU_ALL Referencing files: Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst This is an old snapshot of the code. I update this from the real rcu_prepare_for_idle() function in kernel/rcu/tree_plugin.h. This change was tested by invoking "make htmldocs". 4. RCU_TORTURE_TESTS Referencing files: kernel/rcu/rcutorture.c Forward-progress checking conflicts with CPU-stall testing, so we should complain at "modprobe rcutorture" when both are enabled. Signed-off-by: Zhouyi Zhou Signed-off-by: Paul E. McKenney

rcu/doc: Add a quick quiz to explain further why we need smp_mb__after_unlock_lock()

2021-07-20T20:36:33Z

Add some missing critical pieces of explanation to understand the need for full memory barriers throughout the whole grace period state machine, thanks to Paul's explanations. Signed-off-by: Frederic Weisbecker Cc: Neeraj Upadhyay Cc: Joel Fernandes Cc: Uladzislau Rezki Cc: Boqun Feng [ paulmck: Adjust code block per Akira Yokosawa. ] Signed-off-by: Paul E. McKenney

doc: Fix diagram references in memory-ordering document

2021-05-10T22:39:19Z

The three diagrams describing rcu_gp_init() all spuriously refer to the same figure, probably due to a copy/paste issue. This commit fixes these references. Signed-off-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney

doc: Fix statement of RCU's memory-ordering requirements

2021-05-10T22:39:19Z

The sentence defining the relationship of accesses before a grace period to read-side accesses following that same grace period was missing a small word: "not". This commit therefore adds it. Reported-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney

docs: Fix reST markup when linking to sections

2020-12-31T22:44:47Z

During the process of converting the documentation to reST, some links were converted using the following wrong syntax (and sometimes using %20 instead of spaces): `Display text <#section-name-in-html>`__ This syntax isn't valid according to the docutils' spec [1], but more importantly, it is specific to HTML, since it uses '#' to link to an HTML anchor. The right syntax would instead use a docutils hyperlink reference as the embedded URI to point to the section [2], that is: `Display text

`__ This syntax works in both HTML and PDF. The LaTeX toolchain doesn't mind the HTML anchor syntax when generating the pdf documentation (make pdfdocs), that is, the build succeeds but the links don't work, but that syntax causes errors when trying to build using the not-yet-merged rst2pdf: ValueError: format not resolved, probably missing URL scheme or undefined destination target for 'Forcing%20Quiescent%20States' So, use the correct syntax in order to have it work in all different output formats. [1]: https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#reference-names [2]: https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#embedded-uris-and-aliases Fixes: ccc9971e2147 ("docs: rcu: convert some articles from html to ReST") Fixes: c8cce10a62aa ("docs: Fix the reference labels in Locking.rst") Fixes: e548cdeffcd8 ("docs-rst: convert kernel-locking to ReST") Fixes: 7ddedebb03b7 ("ALSA: doc: ReSTize writing-an-alsa-driver document") Signed-off-by: Nícolas F. R. A. Prado Reviewed-by: Takashi Iwai Reviewed-by: Mauro Carvalho Chehab Link: https://lore.kernel.org/r/20201228144537.135353-1-nfraprado@protonmail.com Signed-off-by: Jonathan Corbet