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3e31009898
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(). ] |
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ABI | ||
accelerators | ||
accounting | ||
acpi | ||
admin-guide | ||
aoe | ||
arm | ||
arm64 | ||
auxdisplay | ||
backlight | ||
block | ||
blockdev | ||
bpf | ||
bus-devices | ||
cdrom | ||
cgroup-v1 | ||
cma | ||
connector | ||
console | ||
core-api | ||
cpu-freq | ||
cpuidle | ||
crypto | ||
dev-tools | ||
device-mapper | ||
devicetree | ||
doc-guide | ||
driver-api | ||
driver-model | ||
early-userspace | ||
EDID | ||
extcon | ||
fault-injection | ||
fb | ||
features | ||
filesystems | ||
firmware_class | ||
fmc | ||
fpga | ||
gpio | ||
gpu | ||
hid | ||
hwmon | ||
i2c | ||
ia64 | ||
ide | ||
iio | ||
infiniband | ||
input | ||
ioctl | ||
isdn | ||
kbuild | ||
kdump | ||
kernel-hacking | ||
laptops | ||
leds | ||
lightnvm | ||
livepatch | ||
locking | ||
m68k | ||
maintainer | ||
md | ||
media | ||
memory-devices | ||
mic | ||
mips | ||
misc-devices | ||
mmc | ||
mtd | ||
namespaces | ||
netlabel | ||
networking | ||
nfc | ||
nios2 | ||
nvdimm | ||
nvmem | ||
openrisc | ||
parisc | ||
PCI | ||
pcmcia | ||
perf | ||
phy | ||
platform | ||
power | ||
powerpc | ||
pps | ||
process | ||
pti | ||
ptp | ||
rapidio | ||
RCU | ||
riscv | ||
s390 | ||
scheduler | ||
scsi | ||
security | ||
serial | ||
sh | ||
sound | ||
sparc | ||
sphinx | ||
sphinx-static | ||
spi | ||
sysctl | ||
target | ||
thermal | ||
timers | ||
trace | ||
translations | ||
usb | ||
userspace-api | ||
virtual | ||
vm | ||
w1 | ||
watchdog | ||
wimax | ||
x86 | ||
xtensa | ||
.gitignore | ||
00-INDEX | ||
atomic_bitops.txt | ||
atomic_t.txt | ||
bt8xxgpio.txt | ||
btmrvl.txt | ||
bus-virt-phys-mapping.txt | ||
Changes | ||
clearing-warn-once.txt | ||
CodingStyle | ||
conf.py | ||
cpu-load.txt | ||
cputopology.txt | ||
crc32.txt | ||
dcdbas.txt | ||
debugging-modules.txt | ||
debugging-via-ohci1394.txt | ||
dell_rbu.txt | ||
digsig.txt | ||
DMA-API-HOWTO.txt | ||
DMA-API.txt | ||
DMA-attributes.txt | ||
DMA-ISA-LPC.txt | ||
docutils.conf | ||
dontdiff | ||
efi-stub.txt | ||
eisa.txt | ||
flexible-arrays.txt | ||
futex-requeue-pi.txt | ||
gcc-plugins.txt | ||
highuid.txt | ||
hw_random.txt | ||
hwspinlock.txt | ||
index.rst | ||
intel_txt.txt | ||
Intel-IOMMU.txt | ||
io_ordering.txt | ||
io-mapping.txt | ||
iostats.txt | ||
IPMI.txt | ||
IRQ-affinity.txt | ||
IRQ-domain.txt | ||
IRQ.txt | ||
irqflags-tracing.txt | ||
isa.txt | ||
isapnp.txt | ||
kernel-per-CPU-kthreads.txt | ||
kobject.txt | ||
kprobes.txt | ||
kref.txt | ||
ldm.txt | ||
lockup-watchdogs.txt | ||
logo.gif | ||
logo.txt | ||
lsm.txt | ||
lzo.txt | ||
mailbox.txt | ||
Makefile | ||
memory-barriers.txt | ||
memory-hotplug.txt | ||
men-chameleon-bus.txt | ||
nommu-mmap.txt | ||
ntb.txt | ||
numastat.txt | ||
padata.txt | ||
parport-lowlevel.txt | ||
percpu-rw-semaphore.txt | ||
phy.txt | ||
pi-futex.txt | ||
pnp.txt | ||
preempt-locking.txt | ||
pwm.txt | ||
rbtree.txt | ||
remoteproc.txt | ||
rfkill.txt | ||
robust-futex-ABI.txt | ||
robust-futexes.txt | ||
rpmsg.txt | ||
rtc.txt | ||
SAK.txt | ||
sgi-ioc4.txt | ||
siphash.txt | ||
SM501.txt | ||
smsc_ece1099.txt | ||
speculation.txt | ||
static-keys.txt | ||
SubmittingPatches | ||
svga.txt | ||
switchtec.txt | ||
sync_file.txt | ||
tee.txt | ||
this_cpu_ops.txt | ||
unaligned-memory-access.txt | ||
vfio-mediated-device.txt | ||
vfio.txt | ||
video-output.txt | ||
xillybus.txt | ||
xz.txt | ||
zorro.txt |