Currently both expedited and regular grace period stall warnings use
a single timeout value that with units of seconds. However, recent
Android use cases problem require a sub-100-millisecond expedited RCU CPU
stall warning. Given that expedited RCU grace periods normally complete
in far less than a single millisecond, especially for small systems,
this is not unreasonable.
Therefore introduce the CONFIG_RCU_EXP_CPU_STALL_TIMEOUT kernel
configuration that defaults to 20 msec on Android and remains the same
as that of the non-expedited stall warnings otherwise. It also can be
changed in run-time via: /sys/.../parameters/rcu_exp_cpu_stall_timeout.
[ paulmck: Default of zero to use CONFIG_RCU_STALL_TIMEOUT. ]
Signed-off-by: Uladzislau Rezki <uladzislau.rezki@sony.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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- out-of-date plaintext file names (*.txt) -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>
All of the uses of CONFIG_RCU_FAST_NO_HZ=y that I have seen involve
systems with RCU callbacks offloaded. In this situation, all that this
Kconfig option does is slow down idle entry/exit with an additional
allways-taken early exit. If this is the only use case, then this
Kconfig option nothing but an attractive nuisance that needs to go away.
This commit therefore removes the RCU_FAST_NO_HZ Kconfig option.
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>
The reader-writer-lock analogy is a useful way to think about RCU, but
it is not always applicable. It is useful to have other analogies to
work with, and particularly to emphasise that no single analogy is
perfect.
This patch add a "RCU as reference count" to the "what is RCU" document.
See https://lwn.net/Articles/872559/
[ paulmck: Apply Akira Yokosawa feedback. ]
Reviewed-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>
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>
This commit adds a bullet item noting that both deficiencies and surpluses
of calls to rcu_*_enter() and rcu_*_exit() can result in RCU CPU stall
warnings.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit calls out the possibility of self-detected stalls, adds new
messages, and calls out the use for stack traces.
Reported-by: Jeff Layton <jlayton@kernel.org>
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>
"-foo-" does not work as emphasis in ReST markdown.
Use "*foo*" instead.
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Pull RCU updates from Paul McKenney:
- Bitmap parsing support for "all" as an alias for all bits
- Documentation updates
- Miscellaneous fixes, including some that overlap into mm and lockdep
- kvfree_rcu() updates
- mem_dump_obj() updates, with acks from one of the slab-allocator
maintainers
- RCU NOCB CPU updates, including limited deoffloading
- SRCU updates
- Tasks-RCU updates
- Torture-test updates
* 'core-rcu-2021.07.04' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (78 commits)
tasks-rcu: Make show_rcu_tasks_gp_kthreads() be static inline
rcu-tasks: Make ksoftirqd provide RCU Tasks quiescent states
rcu: Add missing __releases() annotation
rcu: Remove obsolete rcu_read_unlock() deadlock commentary
rcu: Improve comments describing RCU read-side critical sections
rcu: Create an unrcu_pointer() to remove __rcu from a pointer
srcu: Early test SRCU polling start
rcu: Fix various typos in comments
rcu/nocb: Unify timers
rcu/nocb: Prepare for fine-grained deferred wakeup
rcu/nocb: Only cancel nocb timer if not polling
rcu/nocb: Delete bypass_timer upon nocb_gp wakeup
rcu/nocb: Cancel nocb_timer upon nocb_gp wakeup
rcu/nocb: Allow de-offloading rdp leader
rcu/nocb: Directly call __wake_nocb_gp() from bypass timer
rcu: Don't penalize priority boosting when there is nothing to boost
rcu: Point to documentation of ordering guarantees
rcu: Make rcu_gp_cleanup() be noinline for tracing
rcu: Restrict RCU_STRICT_GRACE_PERIOD to at most four CPUs
rcu: Make show_rcu_gp_kthreads() dump rcu_node structures blocking GP
...
This commit clarifies which primitives readers can use given that the
corresponding updaters have made a specific choice. This commit also adds
this information for the various RCU Tasks flavors. While in the area, it
removes a paragraph that no longer applies in any straightforward manner.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210624160609.292325-3-toke@redhat.com
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>
This commit replaces "Steve" with the his real name, which is "Stephen".
Reported-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Pull documentation updates from Jonathan Corbet:
"It has been a relatively quiet cycle in docsland.
- As promised, the minimum Sphinx version to build the docs is now
1.7, and we have dropped support for Python 2 entirely. That
allowed the removal of a bunch of compatibility code.
- A set of treewide warning fixups from Mauro that I applied after it
became clear nobody else was going to deal with them.
- The automarkup mechanism can now create cross-references from
relative paths to RST files.
- More translations, typo fixes, and warning fixes"
* tag 'docs-5.12' of git://git.lwn.net/linux: (75 commits)
docs: kernel-hacking: be more civil
docs: Remove the Microsoft rhetoric
Documentation/admin-guide: kernel-parameters: Update nohlt section
doc/admin-guide: fix spelling mistake: "perfomance" -> "performance"
docs: Document cross-referencing using relative path
docs: Enable usage of relative paths to docs on automarkup
docs: thermal: fix spelling mistakes
Documentation: admin-guide: Update kvm/xen config option
docs: Make syscalls' helpers naming consistent
coding-style.rst: Avoid comma statements
Documentation: /proc/loadavg: add 3 more field descriptions
Documentation/submitting-patches: Add blurb about backtraces in commit messages
Docs: drop Python 2 support
Move our minimum Sphinx version to 1.7
Documentation: input: define ABS_PRESSURE/ABS_MT_PRESSURE resolution as grams
scripts/kernel-doc: add internal hyperlink to DOC: sections
Update Documentation/admin-guide/sysctl/fs.rst
docs: Update DTB format references
docs: zh_CN: add iio index.rst translation
docs/zh_CN: add iio ep93xx_adc.rst translation
...
Pull RCU updates from Ingo Molnar:
"These are the latest RCU updates for v5.12:
- 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.
- nolibc fixes for the torture tests"
* tag 'core-rcu-2021-02-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (130 commits)
percpu_ref: Dump mem_dump_obj() info upon reference-count underflow
rcu: Make call_rcu() print mem_dump_obj() info for double-freed callback
mm: Make mem_obj_dump() vmalloc() dumps include start and length
mm: Make mem_dump_obj() handle vmalloc() memory
mm: Make mem_dump_obj() handle NULL and zero-sized pointers
mm: Add mem_dump_obj() to print source of memory block
tools/rcutorture: Fix position of -lgcc in mkinitrd.sh
tools/nolibc: Fix position of -lgcc in the documented example
tools/nolibc: Emit detailed error for missing alternate syscall number definitions
tools/nolibc: Remove incorrect definitions of __ARCH_WANT_*
tools/nolibc: Get timeval, timespec and timezone from linux/time.h
tools/nolibc: Implement poll() based on ppoll()
tools/nolibc: Implement fork() based on clone()
tools/nolibc: Make getpgrp() fall back to getpgid(0)
tools/nolibc: Make dup2() rely on dup3() when available
tools/nolibc: Add the definition for dup()
rcutorture: Add rcutree.use_softirq=0 to RUDE01 and TASKS01
torture: Maintain torture-specific set of CPUs-online books
torture: Clean up after torture-test CPU hotplugging
rcutorture: Make object_debug also double call_rcu() heap object
...
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>
