WSL2-Linux-Kernel/Documentation
Paul E. McKenney 3e31009898 rcu: Defer reporting RCU-preempt quiescent states when disabled
This commit defers reporting of RCU-preempt quiescent states at
rcu_read_unlock_special() time when any of interrupts, softirq, or
preemption are disabled.  These deferred quiescent states are reported
at a later RCU_SOFTIRQ, context switch, idle entry, or CPU-hotplug
offline operation.  Of course, if another RCU read-side critical
section has started in the meantime, the reporting of the quiescent
state will be further deferred.

This also means that disabling preemption, interrupts, and/or
softirqs will act as an RCU-preempt read-side critical section.
This is enforced by checking preempt_count() as needed.

Some special cases must be handled on an ad-hoc basis, for example,
context switch is a quiescent state even though both the scheduler and
do_exit() disable preemption.  In these cases, additional calls to
rcu_preempt_deferred_qs() override the preemption disabling.  Similar
logic overrides disabled interrupts in rcu_preempt_check_callbacks()
because in this case the quiescent state happened just before the
corresponding scheduling-clock interrupt.

In theory, this change lifts a long-standing restriction that required
that if interrupts were disabled across a call to rcu_read_unlock()
that the matching rcu_read_lock() also be contained within that
interrupts-disabled region of code.  Because the reporting of the
corresponding RCU-preempt quiescent state is now deferred until
after interrupts have been enabled, it is no longer possible for this
situation to result in deadlocks involving the scheduler's runqueue and
priority-inheritance locks.  This may allow some code simplification that
might reduce interrupt latency a bit.  Unfortunately, in practice this
would also defer deboosting a low-priority task that had been subjected
to RCU priority boosting, so real-time-response considerations might
well force this restriction to remain in place.

Because RCU-preempt grace periods are now blocked not only by RCU
read-side critical sections, but also by disabling of interrupts,
preemption, and softirqs, it will be possible to eliminate RCU-bh and
RCU-sched in favor of RCU-preempt in CONFIG_PREEMPT=y kernels.  This may
require some additional plumbing to provide the network denial-of-service
guarantees that have been traditionally provided by RCU-bh.  Once these
are in place, CONFIG_PREEMPT=n kernels will be able to fold RCU-bh
into RCU-sched.  This would mean that all kernels would have but
one flavor of RCU, which would open the door to significant code
cleanup.

Moving to a single flavor of RCU would also have the beneficial effect
of reducing the NOCB kthreads by at least a factor of two.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Apply rcu_read_unlock_special() preempt_count() feedback
  from Joel Fernandes. ]
[ paulmck: Adjust rcu_eqs_enter() call to rcu_preempt_deferred_qs() in
  response to bug reports from kbuild test robot. ]
[ paulmck: Fix bug located by kbuild test robot involving recursion
  via rcu_preempt_deferred_qs(). ]
2018-08-30 16:02:34 -07:00
..
ABI platform-drivers-x86 for v4.19-1 2018-08-22 14:14:15 -07:00
EDID
PCI Merge branch 'remotes/lorenzo/pci/dwc' 2018-08-15 14:59:11 -05:00
RCU rcu: Defer reporting RCU-preempt quiescent states when disabled 2018-08-30 16:02:34 -07:00
accelerators ocxl: Document new OCXL IOCTLs 2018-06-03 20:40:33 +10:00
accounting
acpi ACPI: property: graph: Update graph documentation to use generic references 2018-07-23 12:44:52 +02:00
admin-guide IOMMU Update for Linux v4.19 2018-08-24 13:10:38 -07:00
aoe
arm ARM: Device-tree updates 2018-06-11 17:57:38 -07:00
arm64 ARM: 2018-04-09 11:42:31 -07:00
auxdisplay Doc: misc-devices: move lcd-panel-cgram.txt to auxdisplay/ 2018-04-12 16:08:02 +02:00
backlight
block block: Track DISCARD statistics and output them in stat and diskstat 2018-07-18 08:44:22 -06:00
blockdev zram: introduce zram memory tracking 2018-06-07 17:34:34 -07:00
bpf Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2018-08-07 11:02:05 -07:00
bus-devices
cdrom Documentation/cdrom: fix German sharp s in LaTex 2018-03-08 19:35:29 -07:00
cgroup-v1 page cache: use xa_lock 2018-04-11 10:28:39 -07:00
cma
connector
console Documentation: corrections to console/console.txt 2018-08-10 16:09:40 -06:00
core-api docs/core-api: mm-api: add section about GFP flags 2018-08-23 18:48:43 -07:00
cpu-freq cpufreq: Drop cpufreq_table_validate_and_show() 2018-04-10 08:40:45 +02:00
cpuidle cpuidle: Add definition of residency to sysfs documentation 2018-04-09 13:44:37 +02:00
crypto crypto: remove redundant type flags from tfm allocation 2018-07-09 00:30:29 +08:00
dev-tools doc: dev-tools: kselftest.rst: update contributing new tests 2018-06-29 09:01:50 -06:00
device-mapper dm thin: include metadata_low_watermark threshold in pool status 2018-07-30 11:49:08 -04:00
devicetree Merge branch 'irq-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-08-26 09:55:28 -07:00
doc-guide Documentation/sphinx: allow "functions" with no parameters 2018-06-30 07:52:42 -06:00
driver-api Merge branch 'for-4.19' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/libata 2018-08-24 13:20:33 -07:00
driver-model dmaengine: add a new helper dmaenginem_async_device_register 2018-07-30 10:50:22 +05:30
early-userspace initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
extcon
fault-injection Documentation: nvme: Documentation for nvme fault injection 2018-03-26 08:53:43 -06:00
fb Documentation/fb: corrections for fbcon.txt 2018-08-10 17:23:02 +02:00
features ARM: 8777/1: Hook up SYNC_CORE functionality for sys_membarrier() 2018-07-11 11:02:08 +01:00
filesystems Kbuild updates for v4.19 (2nd) 2018-08-25 13:40:38 -07:00
firmware_class
fmc
fpga docs: fpga: add a document for FPGA Device Feature List (DFL) Framework Overview 2018-07-15 13:55:44 +02:00
gpio Documentation: gpio: Move drivers-on-gpio.txt to driver-api 2018-03-23 04:22:29 +01:00
gpu drm/msm/gpu: Add the buffer objects from the submit to the crash dump 2018-07-30 08:50:10 -04:00
hid Documentation: fix input related doc refs 2017-10-12 11:14:06 -06:00
hwmon ARM: SoC driver updates 2018-08-23 13:52:46 -07:00
i2c i2c: ocores: update my email address 2018-08-24 14:46:43 +02:00
ia64 ia64: doc: tweak whitespace for 'console=' parameter 2018-03-05 14:41:38 -08:00
ide
iio iio: adc: New driver for Cirrus Logic EP93xx ADC 2017-07-25 19:56:23 +01:00
infiniband Documentation/ABI: update infiniband sysfs interfaces 2018-02-23 08:18:33 -07:00
input input: add MT_TOOL_DIAL 2018-07-17 15:33:47 +02:00
ioctl Char/Misc driver patches for 4.19-rc1 2018-08-18 11:04:51 -07:00
isdn Documentation/isdn: check and fix dead links ... 2018-03-26 12:31:13 -04:00
kbuild kbuild: Fix LOADLIBES rename in Documentation/kbuild/makefiles.txt 2018-08-22 23:21:42 +09:00
kdump kexec/kdump: minor Documentation updates for arm64 and Image 2017-07-12 16:26:00 -07:00
kernel-hacking doc:it_IT: translation for kernel-hacking 2018-07-26 16:21:09 -06:00
laptops platform/x86: thinkpad_acpi: silence HKEY 0x6032, 0x60f0, 0x6030 2018-05-07 15:10:31 +03:00
leds Documentation: leds: Update 00-INDEX file 2017-10-23 20:17:03 +02:00
lightnvm lightnvm: physical block device (pblk) target 2017-04-16 10:06:33 -06:00
livepatch livepatch: Remove not longer valid limitations from the documentation 2018-05-24 15:37:57 +02:00
locking locking: Implement an algorithm choice for Wound-Wait mutexes 2018-07-03 09:44:36 +02:00
m68k
maintainer docs: Fix more broken references 2018-06-15 18:11:26 -03:00
md raid5-ppl: PPL support for disks with write-back cache enabled 2018-01-15 14:29:42 -08:00
media media: doc: media/v4l-drivers: Update Qualcomm CAMSS driver document for 8x96 2018-08-02 08:48:00 -04:00
memory-devices
mic
mips Documentation: mips: Update AU1xxx_IDE Kconfig dependencies 2018-02-01 12:45:35 -07:00
misc-devices pci_endpoint_test: Add 2 ioctl commands 2018-07-19 11:46:57 +01:00
mmc MMC core: 2017-05-02 17:34:32 -07:00
mtd mtd: spi-nor: add an API to restore the status of SPI flash chip 2017-12-13 00:36:00 +01:00
namespaces
netlabel
networking ARM: SoC driver updates 2018-08-23 13:52:46 -07:00
nfc
nios2
nvdimm
nvmem NVMEM documentation fix: A minor typo 2017-08-24 13:31:58 -06:00
openrisc Documentation: openrisc: Updates to README 2017-10-30 21:37:53 +09:00
parisc
pcmcia pcmcia: remove long deprecated pcmcia_request_exclusive_irq() function 2018-08-18 12:30:42 -07:00
perf drivers/bus: Move Arm CCN PMU driver 2018-03-06 17:26:15 +01:00
phy
platform
power PM / reboot: Eliminate race between reboot and suspend 2018-08-06 12:35:20 +02:00
powerpc powerpc: Document issues with TM on POWER9 2018-07-02 23:54:29 +10:00
pps drivers/pps: aesthetic tweaks to PPS-related content 2017-09-08 18:26:51 -07:00
process Raise the minimum required gcc version to 4.6 2018-08-20 14:12:38 -07:00
pti
ptp ptp: Fix documentation to match code. 2018-03-26 12:13:21 -04:00
rapidio Documentation: rapidio: move sysfs interface to ABI 2018-02-23 08:25:45 -07:00
riscv perf: riscv: Add Document for Future Porting Guide 2018-06-04 14:02:11 -07:00
s390 vfio-ccw: update documentation 2018-03-01 17:32:14 +01:00
scheduler sched/deadline/Documentation: Add overrun signal and GRUB-PA documentation 2018-05-14 09:12:27 +02:00
scsi block: remove BLK_EH_HANDLED 2018-05-29 08:59:21 -06:00
security Kbuild: rename CC_STACKPROTECTOR[_STRONG] config variables 2018-06-14 12:21:18 +09:00
serial tty: n_gsm: do not send/receive in ldisc close path 2017-06-03 18:48:52 +09:00
sh docs-rst: convert sh book to ReST 2017-05-16 08:44:18 -03:00
sound ASoC: Updates for v4.19 2018-08-13 12:12:31 +02:00
sparc sparc64: Add support for ADI (Application Data Integrity) 2018-03-18 07:38:48 -07:00
sphinx Documentation/sphinx: allow "functions" with no parameters 2018-06-30 07:52:42 -06:00
sphinx-static docs RTD theme: code-block with line nos - lines and line numbers don't line up. 2017-07-17 13:48:45 -06:00
spi spi: Document SPI slave controller support 2017-05-26 13:11:00 +01:00
sysctl namei: allow restricted O_CREAT of FIFOs and regular files 2018-08-23 18:48:43 -07:00
target Documentation/target: add an example script to configure an iSCSI target 2017-05-01 22:21:35 -07:00
thermal thermal: Add cooling device's statistics in sysfs 2018-04-02 21:49:01 +08:00
timers timekeeping.txt: Correct maxCount of n-bit binary counter 2018-07-23 09:33:06 -06:00
trace This was a moderately busy cycle for docs, with the usual collection of 2018-08-14 14:29:31 -07:00
translations This was a moderately busy cycle for docs, with the usual collection of 2018-08-14 14:29:31 -07:00
usb USB-serial updates for v4.19-rc1 2018-07-20 21:47:15 +02:00
userspace-api audit/stable-4.18 PR 20180605 2018-06-06 16:34:00 -07:00
virtual KVM: Documentation: rename the capability of KVM_CAP_ARM_SET_SERROR_ESR 2018-08-22 14:08:05 +02:00
vm docs/vm: move ksm and transhuge from "user" to "internals" section. 2018-05-29 06:45:55 -06:00
w1 w1: fix w1_ds2438 documentation 2018-07-07 17:27:13 +02:00
watchdog watchdog: remove bfin_wdt driver 2018-03-26 15:57:04 +02:00
wimax
x86 Merge branch 'x86-timers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-08-13 18:28:19 -07:00
xtensa xtensa: add support for KASAN 2017-12-16 22:37:12 -08:00
.gitignore
00-INDEX docs: admin-guide: add cgroup-v2 documentation 2018-05-10 15:42:41 -06:00
Changes
CodingStyle
DMA-API-HOWTO.txt DMA-API-HOWTO.txt: standardize document format 2017-07-14 13:51:32 -06:00
DMA-API.txt dma-coherent: remove the DMA_MEMORY_MAP and DMA_MEMORY_IO flags 2017-09-01 11:59:17 +02:00
DMA-ISA-LPC.txt DMA-ISA-LPC.txt: standardize document format 2017-07-14 13:51:33 -06:00
DMA-attributes.txt DMA-attributes.txt: standardize document format 2017-07-14 13:51:33 -06:00
IPMI.txt ipmi: Make IPMI panic strings always available 2017-09-27 16:03:45 -05:00
IRQ-affinity.txt IRQ-affinity.txt: standardize document format 2017-07-14 13:51:41 -06:00
IRQ-domain.txt irqdomain: Kill CONFIG_IRQ_DOMAIN_DEBUG 2018-01-24 12:32:58 +01:00
IRQ.txt IRQ.txt: add a markup for its title 2017-07-14 13:51:42 -06:00
Intel-IOMMU.txt Intel-IOMMU.txt: standardize document format 2017-07-14 13:51:38 -06:00
Makefile Documentation: add script and build target to check for broken file references 2017-10-12 11:07:42 -06:00
SAK.txt SAK.txt: standardize document format 2017-07-14 13:58:04 -06:00
SM501.txt SM501.txt: standardize document format 2017-07-14 13:58:06 -06:00
SubmittingPatches
atomic_bitops.txt locking/atomic/bitops: Document and clarify ordering semantics for failed test_and_{}_bit() 2018-02-13 14:55:53 +01:00
atomic_t.txt Documentation/locking/atomic: Finish the document... 2017-08-25 11:06:33 +02:00
bt8xxgpio.txt bt8xxgpio.txt: standardize document format 2017-07-14 13:51:27 -06:00
btmrvl.txt btmrvl.txt: standardize document format 2017-07-14 13:51:27 -06:00
bus-virt-phys-mapping.txt bus-virt-phys-mapping.txt: standardize document format 2017-07-14 13:51:28 -06:00
clearing-warn-once.txt kernel debug: support resetting WARN*_ONCE 2017-11-17 16:10:00 -08:00
conf.py ext4: import inode data fork chapter from wiki page 2018-07-29 15:45:00 -04:00
cpu-load.txt cpu-load: standardize document format 2017-07-14 13:51:30 -06:00
cputopology.txt cputopology.txt: standardize document format 2017-07-14 13:51:30 -06:00
crc32.txt crc32.txt: standardize document format 2017-07-14 13:51:30 -06:00
dcdbas.txt dcdbas.txt: standardize document format 2017-07-14 13:51:31 -06:00
debugging-modules.txt
debugging-via-ohci1394.txt debugging-via-ohci1394.txt: standardize document format 2017-07-14 13:51:34 -06:00
dell_rbu.txt Documentation: remove stale firmware API reference 2018-05-14 16:44:41 +02:00
digsig.txt digsig.txt: standardize document format 2017-07-14 13:51:31 -06:00
docutils.conf
dontdiff Remove gperf usage from toolchain 2017-08-19 11:02:53 -07:00
efi-stub.txt efi-stub.txt: standardize document format 2017-07-14 13:51:34 -06:00
eisa.txt eisa.txt: standardize document format 2017-07-14 13:51:34 -06:00
flexible-arrays.txt flexible-arrays.txt: standardize document format 2017-07-14 13:51:35 -06:00
futex-requeue-pi.txt futex-requeue-pi.txt: standardize document format 2017-07-14 13:51:35 -06:00
gcc-plugins.txt gcc-plugins.txt: standardize document format 2017-07-14 13:51:36 -06:00
highuid.txt highuid.txt: standardize document format 2017-07-14 13:51:36 -06:00
hw_random.txt hw_random.txt: standardize document format 2017-07-14 13:51:37 -06:00
hwspinlock.txt hwspinlock.txt: standardize document format 2017-07-14 13:51:37 -06:00
index.rst Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2018-08-15 15:04:25 -07:00
intel_txt.txt intel_txt.txt: standardize document format 2017-07-14 13:51:38 -06:00
io-mapping.txt io-mapping.txt: standardize document format 2017-07-14 13:51:38 -06:00
io_ordering.txt io_ordering.txt: standardize document format 2017-07-14 13:51:39 -06:00
iostats.txt block: Track DISCARD statistics and output them in stat and diskstat 2018-07-18 08:44:22 -06:00
irqflags-tracing.txt irqflags-tracing.txt: standardize document format 2017-07-14 13:51:42 -06:00
isa.txt isa.txt: standardize document format 2017-07-14 13:51:43 -06:00
isapnp.txt isapnp.txt: promote title level 2017-07-14 13:51:43 -06:00
kernel-per-CPU-kthreads.txt kernel-per-CPU-kthreads.txt: standardize document format 2017-07-14 13:51:43 -06:00
kobject.txt kobject.txt: standardize document format 2017-07-14 13:51:44 -06:00
kprobes.txt kprobes/Documentation: Fix various typos 2018-06-22 11:10:55 +02:00
kref.txt kref.txt: standardize document format 2017-07-14 13:51:45 -06:00
ldm.txt ldm.txt: standardize document format 2017-07-14 13:51:45 -06:00
lockup-watchdogs.txt lockup-watchdogs.txt: standardize document format 2017-07-14 13:51:46 -06:00
logo.gif
logo.txt
lsm.txt docs-rst: convert lsm from DocBook to ReST 2017-05-16 08:44:19 -03:00
lzo.txt lzo.txt: standardize document format 2017-07-14 13:51:46 -06:00
mailbox.txt mailbox.txt: standardize document format 2017-07-14 13:51:47 -06:00
memory-barriers.txt sched/Documentation: Update wake_up() & co. memory-barrier guarantees 2018-07-17 09:30:34 +02:00
memory-hotplug.txt memory-hotplug.txt: standardize document format 2017-07-14 13:57:53 -06:00
men-chameleon-bus.txt men-chameleon-bus.txt: standardize document format 2017-07-14 13:57:54 -06:00
nommu-mmap.txt Documentation: nommu-map: Fix duplicate word typo 2018-06-26 09:01:27 -06:00
ntb.txt This series converts a number of top-level documents to the RST format 2017-07-15 12:58:58 -07:00
numastat.txt numastat.txt: standardize document format 2017-07-14 13:57:56 -06:00
padata.txt padata.txt: standardize document format 2017-07-14 13:57:56 -06:00
parport-lowlevel.txt parport-lowlevel.txt: standardize document format 2017-07-14 13:57:57 -06:00
percpu-rw-semaphore.txt percpu-rw-semaphore.txt: standardize document format 2017-07-14 13:57:58 -06:00
phy.txt phy.txt: standardize document format 2017-07-14 13:57:58 -06:00
pi-futex.txt Documentation: fix locking rt-mutex doc refs 2017-10-19 12:56:44 -06:00
pnp.txt pnp.txt: standardize document format 2017-07-14 13:57:59 -06:00
preempt-locking.txt preempt-locking.txt: standardize document format 2017-07-14 13:58:00 -06:00
pwm.txt pwm: Standardize document format 2017-07-06 08:23:30 +02:00
rbtree.txt rbtree: cache leftmost node internally 2017-09-08 18:26:48 -07:00
remoteproc.txt remoteproc.txt: standardize document format 2017-07-14 13:58:02 -06:00
rfkill.txt rfkill: Fix several typos in documentation 2018-06-15 13:36:08 +02:00
robust-futex-ABI.txt robust-futex-ABI.txt: standardize document format 2017-07-14 13:58:03 -06:00
robust-futexes.txt robust-futexes.txt: standardize document format 2017-07-14 13:58:03 -06:00
rpmsg.txt rpmsg.txt: standardize document format 2017-07-14 13:58:04 -06:00
rtc.txt Documentation: rtc: move iotcl interface documentation to ABI 2018-01-12 00:20:41 +01:00
sgi-ioc4.txt sgi-ioc4.txt: standardize document format 2017-07-14 13:58:05 -06:00
siphash.txt siphash.txt: standardize document format 2017-07-14 13:58:06 -06:00
smsc_ece1099.txt smsc_ece1099.txt: standardize document format 2017-07-14 13:58:07 -06:00
speculation.txt Documentation: Document array_index_nospec 2018-01-30 21:54:28 +01:00
static-keys.txt jump_label: Provide hotplug context variants 2017-08-10 12:28:59 +02:00
svga.txt documentation/svga.txt: update outdated file 2017-11-20 10:45:50 -07:00
switchtec.txt NTB: switchtec_ntb: Update switchtec documentation with notes for NTB 2017-11-18 20:37:13 -05:00
sync_file.txt sync_file.txt: standardize document format 2017-05-24 13:01:27 -03:00
tee.txt tee.txt: standardize document format 2017-07-14 13:58:14 -06:00
this_cpu_ops.txt this_cpu_ops.txt: standardize document format 2017-07-14 13:58:08 -06:00
unaligned-memory-access.txt unaligned-memory-access.txt: standardize document format 2017-07-14 13:58:09 -06:00
vfio-mediated-device.txt vfio/mdev: Check globally for duplicate devices 2018-06-08 10:24:27 -06:00
vfio.txt vfio: fix documentation 2018-05-08 09:16:41 -06:00
video-output.txt
xillybus.txt xillybus.txt: standardize document format 2017-07-14 13:58:11 -06:00
xz.txt xz.txt: standardize document format 2017-07-14 13:58:11 -06:00
zorro.txt zorro.txt: standardize document format 2017-07-14 13:58:12 -06:00