The RCU dynticks counter is going to be merged into the context tracking
subsystem. Prepare with moving the NMI extended quiescent states
entrypoints to context tracking. For now those are dumb redirection to
existing RCU calls.
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Uladzislau Rezki <uladzislau.rezki@sony.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicolas Saenz Julienne <nsaenz@kernel.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Cc: Yu Liao <liaoyu15@huawei.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Paul Gortmaker<paul.gortmaker@windriver.com>
Cc: Alex Belits <abelits@marvell.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Tested-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
The RCU dynticks counter is going to be merged into the context tracking
subsystem. Prepare with moving the IRQ extended quiescent states
entrypoints to context tracking. For now those are dumb redirection to
existing RCU calls.
[ paulmck: Apply Stephen Rothwell feedback from -next. ]
[ paulmck: Apply Nathan Chancellor feedback. ]
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Uladzislau Rezki <uladzislau.rezki@sony.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicolas Saenz Julienne <nsaenz@kernel.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Cc: Yu Liao <liaoyu15@huawei.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Paul Gortmaker<paul.gortmaker@windriver.com>
Cc: Alex Belits <abelits@marvell.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Tested-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
The RCU documentation contains old-style cross references which
do not follow the best practices outlined in doc-guide/sphinx.rst.
In addition, some of the cross references use URLs that should be replaced
by pathnames.
Update all of these cross references and adjust the surrounding words.
Summary of changes:
- out-of-date plaintext file names (*.txt) -> *.rst
- references by :ref: tags -> path names of *.rst
* use relative paths to .rst files under the RCU/ subdirectory
* use abs paths of Documentation/xxx for other .rst files
- references by URL under https://www.kernel.org/ -> paths of *.rst
- adjust surrounding words of some of updated references.
Note:
The automarkup.py script interprets references via "*.txt" as if they
were via "*.rst", so the *.txt -> *.rst changes should be regarded as
cleanups rather than bug fixes.
Cc: rcu@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Tested-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit belatedly adds documentation of Tasks Rude RCU and Tasks
Trace RCU to RCU's requirements document.
Tested-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
On Ubuntu Focal, strings in some of SVG files under
Documentation/RCU/Design can not be rendered properly when
converted to PDF.
Ubuntu releases since Focal and Debian bullseye have trouble
with "Symbol" font-family in SVG files.
As those strings are mostly API names such as "READ_ONCE()",
"WRITE_ONCE(), "rcu_read_lock()", and so on, using a generic
monospace font-family should be a good alternative.
Substitute the font-family name by a simple sed pattern:
's/Symbol/monospace/g'
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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
75c27f119b ("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 <zhouzhouyi@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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 <frederic@kernel.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
[ paulmck: Adjust code block per Akira Yokosawa. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
To avoid the ``foo`` markup inside the `bar`__ hyperlink marker,
use the "replace" directive [1].
This should restore the intended appearance of the link.
Tested with sphinx versions 1.7.9 and 2.4.4.
[1]: https://docutils.sourceforge.io/docs/ref/rst/directives.html#replace
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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 <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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 <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Pull RCU updates from Paul E. McKenney:
- Documentation updates.
- Miscellaneous fixes.
- kfree_rcu() updates: Addition of mem_dump_obj() to provide allocator return
addresses to more easily locate bugs. This has a couple of RCU-related commits,
but is mostly MM. Was pulled in with akpm's agreement.
- Per-callback-batch tracking of numbers of callbacks,
which enables better debugging information and smarter
reactions to large numbers of callbacks.
- The first round of changes to allow CPUs to be runtime switched from and to
callback-offloaded state.
- CONFIG_PREEMPT_RT-related changes.
- RCU CPU stall warning updates.
- Addition of polling grace-period APIs for SRCU.
- Torture-test and torture-test scripting updates, including a "torture everything"
script that runs rcutorture, locktorture, scftorture, rcuscale, and refscale.
Plus does an allmodconfig build.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
CONFIG_PREEMPTION is selected by CONFIG_PREEMPT and by CONFIG_PREEMPT_RT.
Both PREEMPT and PREEMPT_RT require the same functionality which today
depends on CONFIG_PREEMPT.
Update the documents and mention CONFIG_PREEMPTION. Spell out
CONFIG_PREEMPT_RT (instead PREEMPT_RT) since it is an option now.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The PREEMPT_RT wiki moved from kernel.org to the Linux Foundation wiki.
The kernel.org wiki is read only.
This commit therefore updates the URL of the active PREEMPT_RT wiki.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds requirements documentation for the
get_state_synchronize_srcu(), start_poll_synchronize_srcu(), and
poll_state_synchronize_srcu() functions.
Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/
Reported-by: Kent Overstreet <kent.overstreet@gmail.com>
Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Back in the day, RCU_INIT_POINTER() was the only way to avoid
memory-barrier instructions while storing NULL to an RCU-protected
pointer. Fortunately, in 2016, rcu_assign_pointer() started checking for
compile-time NULL pointers and omitting the memory-barrier instructions in
that case. Unfortunately, RCU's Requirements.rst document was not updated
accordingly. This commit therefore at long last carries out that update.
Fixes: 3a37f7275c ("rcu: No ordering for rcu_assign_pointer() of NULL")
Link: https://lore.kernel.org/lkml/20201209230755.GV7338@casper.infradead.org/
Reported-by: Matthew Wilcox <willy@infradead.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
It appears the Compaq link moved to a machine at HP for a while
after the merger of the two, but that doesn't work either. A search
of HP for "wiz_2637" (w and w/o html suffix) comes up empty.
Since the references aren't critical to the documents we remove them.
Also, the lkml.kernel.org/g links have been broken for ages, so replace
them with lore.kernel.org/r links - standardize on lore for all links too.
Note that we put off fixing these 4y ago - presumably thinking that a
treewide fixup was pending. Probably safe to go fix the RCU ones now.
https://lore.kernel.org/r/20160915144926.GD10850@linux.vnet.ibm.com/
Cc: Michael Opdenacker <michael.opdenacker@free-electrons.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
synchronize_rcu_bh(), synchronize_rcu_bh_expedited(), call_rcu_bh(),
rcu_barrier_bh(), synchronize_sched(), synchronize_rcu_sched_expedited(),
call_rcu_sched(), and rcu_barrier_sched() no longer exist, so this
commit removes mention of them.
Reported-by: Joel Fernandes <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The docbook system has learned that "()" designates a function, so
this commit removes the no-longer-needed "``" to improve readability
of the raw .rst file.
Reported-by: Peter Zijlstra <peterz@infradead.org>
Cc: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
[ paulmck: Apply Stephen Rothwell feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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 <Section Name_>`__
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: ccc9971e21 ("docs: rcu: convert some articles from html to ReST")
Fixes: c8cce10a62 ("docs: Fix the reference labels in Locking.rst")
Fixes: e548cdeffc ("docs-rst: convert kernel-locking to ReST")
Fixes: 7ddedebb03 ("ALSA: doc: ReSTize writing-an-alsa-driver document")
Signed-off-by: Nícolas F. R. A. Prado <nfraprado@protonmail.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/20201228144537.135353-1-nfraprado@protonmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
As warned by Sphinx:
.../Documentation/RCU/Design/Requirements/Requirements.rst:1959: WARNING: Unexpected indentation.
The list block is missing a space before it, making Sphinx to get
it wrong. This commit therefore adds the missing space characters.
Fixes: 2a721e5f0b2c ("docs: Update RCU's hotplug requirements with a bit about design")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The rcu_barrier() section of the "Hotplug CPU" section discusses
deadlocks, however the description of deadlocks other than those involving
rcu_barrier() is rather incomplete.
This commit therefore continues the section by describing how RCU's
design handles CPU hotplug in a deadlock-free way.
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Drop the doubled words "to" and "for".
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: rcu@vger.kernel.org
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Drop the doubled word "the".
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: rcu@vger.kernel.org
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The [smp_]read_barrier_depends() barrier macros no longer exist as
part of the Linux memory model, so remove all references to them from
the Documentation/ directory.
Although this is fairly mechanical on the whole, we drop the "CACHE
COHERENCY" section entirely from 'memory-barriers.txt' as it doesn't
make any sense now that the dependency barriers have been removed.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
Protecting the code in a trampoline can also require protecting a
number of instructions prior to actually entering the trampoline.
For example, these earlier instructions might be computing the address
of the trampoline. This commit therefore updates RCU's requirements to
record this for posterity.
Link: https://lore.kernel.org/lkml/20200511154824.09a18c46@gandalf.local.home/
Reported-by: Lai Jiangshan <jiangshanlai@gmail.com>
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The scheduler is currently required to hold rq/pi locks across the entire
RCU read-side critical section or not at all. This is inconvenient and
leaves traps for the unwary, including the author of this commit.
But now that excessively long grace periods enable scheduling-clock
interrupts for holdout nohz_full CPUs, the nohz_full rescue logic in
rcu_read_unlock_special() can be dispensed with. In other words, the
rcu_read_unlock_special() function can refrain from doing wakeups unless
such wakeups are guaranteed safe.
This commit therefore avoids unsafe wakeups, freeing the scheduler to
hold rq/pi locks across rcu_read_unlock() even if the corresponding RCU
read-side critical section might have been preempted. This commit also
updates RCU's requirements documentation.
This commit is inspired by a patch from Lai Jiangshan:
https://lore.kernel.org/lkml/20191102124559.1135-2-laijs@linux.alibaba.com
This commit is further intended to be a step towards his goal of permitting
the inlining of RCU-preempt's rcu_read_lock() and rcu_read_unlock().
Cc: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Commit ccc9971e21 ("docs: rcu: convert some articles from html to
ReST") has converted a few of html RCU docs into ReST files, but a few
of html tags which not supported on rst is remaining. This commit
converts those to ReST appropriate alternatives.
Reviewed-by: Madhuparna Bhowmik <madhuparnabhowmik04@gmail.com>
Signed-off-by: SeongJae Park <sjpark@amazon.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
While Paul was explaining some RCU magic I noticed a typo in
rcu_note_context_switch(). As a result, this commit replaces
rcu_node_context_switch() with rcu_note_context_switch().
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This restores docs back in ReST format.
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Added Joel's SoB per Stephen Rothwell feedback. ]
[ paulmck: Joel approved via private email. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This restores docs back in ReST format.
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Added Joel's SoB per Stephen Rothwell feedback. ]
[ paulmck: Joel approved via private email. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Mauro's auto conversion broken these links, fix them.
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
There are 4 RCU articles that are written on html format.
The way they are, they can't be part of the Linux Kernel
documentation body nor share the styles and pdf output.
So, convert them to ReST format.
This way, make htmldocs and make pdfdocs will produce a
documentation output that will be like the original ones, but
will be part of the Linux Kernel documentation body.
Part of the conversion was done with the help of pandoc, but
the result had some broken things that had to be manually
fixed.
Following are manual changes Mauro made when doing the automatic conversion:
Quoting from: https://lore.kernel.org/rcu/20190726154550.5eeae294@coco.lan/
> > At least the pandoc's version I used here has a bug: its conversion
> > from html to ReST on those files only start after a <body> tag - or
> > when the first quiz table starts. I only discovered that adding a
> > <body> at the beginning of the file solve this book at the last
> > conversions.
> >
> > So, for most html->ReST conversions, I manually converted the first
> > part of the document, basically stripping html paragraph tags and
> > by replacing highlights by the ReST syntax.
> >
> > Also, all the quiz tables seem to assume some javascript macro or
> > css style that would be hiding the answer part until the mouse moves
> > to it. Such macro/css was not there at the kernel tree. So, the quiz
> > answers have the same color as the background, making them invisible.
> > Even if we had such macro/css, this is not portable for pdf/LaTeX output
> > (and I'm not sure if this would work with ePub).
> >
> > So, I ended by manually doing the table conversion.
> >
> > Finally, I double-checked if the conversions ended ok, addressing any
> > issues that might have heppened.
> >
> > So, after both automatic conversion and manual fixes, I opened both the
> > html files produced by Sphinx and the original ones and compared them
> > line per line (except for the indexes, as Sphinx produces them
> > automatically), in order to see if all information from the original
> > files will be there on a format close to what we have on other ReST
> > files, fixing any pending issues if any.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This reverts docs from commit 355e9972da81e803bbb825b76106ae9b358caf8e.
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Added Joel's SoB per Stephen Rothwell feedback. ]
[ paulmck: Joel approved via private email. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This reverts docs from commit d6b9cd7dc8e041ee83cb1362fce59a3cdb1f2709.
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Added Joel's SoB per Stephen Rothwell feedback. ]
[ paulmck: Joel approved via private email. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The rcu_dereference_raw_notrace() API name is confusing. It is equivalent
to rcu_dereference_raw() except that it also does sparse pointer checking.
There are only a few users of rcu_dereference_raw_notrace(). This patches
renames all of them to be rcu_dereference_raw_check() with the "_check()"
indicating sparse checking.
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Fix checkpatch warnings about parentheses. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Commit bb73c52bad ("rcu: Don't disable preemption for Tiny and Tree
RCU readers") removed the barrier() calls from rcu_read_lock() and
rcu_write_lock() in CONFIG_PREEMPT=n&&CONFIG_PREEMPT_COUNT=n kernels.
Within RCU, this commit was OK, but it failed to account for things like
get_user() that can pagefault and that can be reordered by the compiler.
Lack of the barrier() calls in rcu_read_lock() and rcu_read_unlock()
can cause these page faults to migrate into RCU read-side critical
sections, which in CONFIG_PREEMPT=n kernels could result in too-short
grace periods and arbitrary misbehavior. Please see commit 386afc9114
("spinlocks and preemption points need to be at least compiler barriers")
and Linus's commit 66be4e66a7 ("rcu: locking and unlocking need to
always be at least barriers"), this last of which restores the barrier()
call to both rcu_read_lock() and rcu_read_unlock().
This commit removes barrier() calls that are no longer needed given that
the addition of them in Linus's commit noted above. The combination of
this commit and Linus's commit effectively reverts commit bb73c52bad
("rcu: Don't disable preemption for Tiny and Tree RCU readers").
Reported-by: Herbert Xu <herbert@gondor.apana.org.au>
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
[ paulmck: Fix embarrassing typo located by Alan Stern. ]
Now that synchronize_rcu_bh, synchronize_rcu_bh_expedited, call_rcu_bh,
rcu_barrier_bh, synchronize_sched, synchronize_sched_expedited,
call_rcu_sched, rcu_barrier_sched, get_state_synchronize_sched,
and cond_synchronize_sched are obsolete, let's remove them from the
documentation aside from a small historical section.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Although the name rcu_process_callbacks() still makes sense for Tiny
RCU, where most of what it does is invoke callbacks, it no longer makes
much sense for Tree RCU, especially given that the actually callback
invocation is relegated to rcu_do_batch(), or, for no-CBs CPUs, to the
rcuo kthreads. Especially in the latter case, rcu_process_callbacks()
has very little to do with actual callbacks. A better description of
this function is that it performs RCU's core processing.
This commit therefore changes the name of Tree RCU's rcu_process_callbacks()
function to rcu_core(), which also has the virtue of being consistent with
the existing invoke_rcu_core() function.
While in the area, the header comment is reworked.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
The name rcu_check_callbacks() arguably made sense back in the early
2000s when RCU was quite a bit simpler than it is today, but it has
become quite misleading, especially with the advent of dyntick-idle
and NO_HZ_FULL. The rcu_check_callbacks() function is RCU's hook into
the scheduling-clock interrupt, and is now but one of many ways that
callbacks get promoted to invocable state.
This commit therefore changes the name to rcu_sched_clock_irq(),
which is the same number of characters and clearly indicates this
function's relation to the rest of the Linux kernel. In addition, for
the sake of consistency, rcu_flavor_check_callbacks() is also renamed
to rcu_flavor_sched_clock_irq().
While in the area, the header comments for both functions are reworked.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
SRCU's synchronize_srcu() may not be invoked from CPU-hotplug notifiers,
due to the fact that SRCU grace periods make use of timers and the
possibility of timers being temporarily stranded on the outgoing CPU.
This stranding of timers means that timers posted to the outgoing CPU
will not fire until late in the CPU-hotplug process. The problem is
that if a notifier is waiting on an SRCU grace period, that grace period
is waiting on a timer, and that timer is stranded on the outgoing CPU,
then the notifier will never be awakened, in other words, deadlock has
occurred. This same situation of course also prohibits srcu_barrier()
from being invoked from CPU-hotplug notifiers.
This commit therefore updates the requirements to include this restriction.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Back when there could be multiple RCU flavors running in the same kernel
at the same time, it was necessary to specify the expedited grace-period
IPI handler at runtime. Now that there is only one RCU flavor, the
IPI handler can be determined at build time. There is therefore no
longer any reason for the RCU-preempt and RCU-sched IPI handlers to
have different names, nor is there any reason to pass these handlers in
function arguments and in the data structures enclosing workqueues.
This commit therefore makes all these changes, pushing the specification
of the expedited grace-period IPI handler down to the point of use.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
This commit replaces "struction" with the correct "structure".
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Given RCU flavor consolidation, when rcu_read_unlock() is invoked with
interrupts disabled, the reporting of the corresponding quiescent state is
deferred until interrupts are re-enabled. There was therefore some hope
that this would allow dropping the restriction against holding scheduler
spinlocks across an rcu_read_unlock() without disabling interrupts across
the entire corresponding RCU read-side critical section. Unfortunately,
the need to quickly provide a quiescent state to expedited grace periods
sometimes requires a call to raise_softirq() during rcu_read_unlock()
execution. Because raise_softirq() can sometimes acquire the scheduler
spinlocks, the restriction must remain in effect. This commit therefore
updates the RCU requirements documentation accordingly.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
The code listing under this section has a quick quiz that says line
19 uses rcu_access_pointer, but the code listing itself instead uses
rcu_dereference(). This commit therefore makes the code listing match
the quick quiz.
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
The Requirements.html document says "Disabling Preemption Does
Not Block Grace Periods". However this is no longer true with
the RCU consolidation. This commit therefore removes the obsolete
(non-)requirement entirely.
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
The rcu_state structure doesn't have a gp_seq_needed field. Update the
description under rcu_data accordingly, to reflect this.
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: <kernel-team@android.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
