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765a3f4fed
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Paul E. McKenney 765a3f4fed rcu: Provide grace-period piggybacking API 
The following pattern is currently not well supported by RCU:

1.	Make data element inaccessible to RCU readers.

2.	Do work that probably lasts for more than one grace period.

3.	Do something to make sure RCU readers in flight before #1 above
	have completed.

Here are some things that could currently be done:

a.	Do a synchronize_rcu() unconditionally at either #1 or #3 above.
	This works, but imposes needless work and latency.

b.	Post an RCU callback at #1 above that does a wakeup, then
	wait for the wakeup at #3.  This works well, but likely results
	in an extra unneeded grace period.  Open-coding this is also
	a bit more semi-tricky code than would be good.

This commit therefore adds get_state_synchronize_rcu() and
cond_synchronize_rcu() APIs.  Call get_state_synchronize_rcu() at #1
above and pass its return value to cond_synchronize_rcu() at #3 above.
This results in a call to synchronize_rcu() if no grace period has
elapsed between #1 and #3, but requires only a load, comparison, and
memory barrier if a full grace period did elapse.

Requested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
2014-03-20 17:12:25 -07:00
..
cpu sched/preempt: Fix up missed PREEMPT_NEED_RESCHED folding 2014-01-13 17:38:55 +01:00
debug kgdb/kdb: Fix no KDB config problem 2014-01-25 08:55:09 +01:00
events This pull request has a new feature to ftrace, namely the trace event 2014-01-22 16:35:21 -08:00
gcov gcov: reuse kbasename helper 2013-11-13 12:09:34 +09:00
irq Merge branches 'irq-urgent-for-linus' and 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-02-15 16:06:12 -08:00
locking rcutorture: Add a lock_busted to test the test 2014-02-23 09:04:43 -08:00
power Merge branch 'for-3.14/core' of git://git.kernel.dk/linux-block 2014-01-30 11:19:05 -08:00
printk printk: flush conflicting continuation line 2014-01-23 16:36:56 -08:00
rcu rcu: Provide grace-period piggybacking API 2014-03-20 17:12:25 -07:00
sched Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-01-31 09:02:51 -08:00
time tick: Clear broadcast pending bit when switching to oneshot 2014-02-13 21:55:54 +01:00
trace ring-buffer: Fix first commit on sub-buffer having non-zero delta 2014-02-11 13:38:54 -05:00
.gitignore Ignore generated file kernel/x509_certificate_list 2013-12-10 18:21:34 +00:00
acct.c
async.c
audit_tree.c fsnotify: remove pointless NULL initializers 2014-01-21 16:19:41 -08:00
audit_watch.c fsnotify: remove pointless NULL initializers 2014-01-21 16:19:41 -08:00
audit.c audit: fix location of __net_initdata for audit_net_ops 2014-01-17 17:14:32 -05:00
audit.h audit: Convert int limit uses to u32 2014-01-14 14:54:00 -05:00
auditfilter.c audit: log on errors from filter user rules 2014-01-13 22:32:31 -05:00
auditsc.c execve: use 'struct filename *' for executable name passing 2014-02-05 12:54:53 -08:00
backtracetest.c
bounds.c mm: do not allocate page->ptl dynamically, if spinlock_t fits to long 2013-12-20 12:25:45 -08:00
capability.c audit: Simplify and correct audit_log_capset 2014-01-13 22:26:48 -05:00
cgroup_freezer.c cgroup: replace cftype->read_seq_string() with cftype->seq_show() 2013-12-05 12:28:04 -05:00
cgroup.c Merge branch 'for-3.14' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup 2014-01-21 17:51:34 -08:00
compat.c
configs.c
context_tracking.c context_tracking: Wrap static key check into more intuitive function name 2013-12-02 20:43:14 +01:00
cpu_pm.c
cpu.c Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2013-11-14 16:55:11 +09:00
cpuset.c cgroup: replace cftype->read_seq_string() with cftype->seq_show() 2013-12-05 12:28:04 -05:00
crash_dump.c
cred.c
delayacct.c kernel/delayacct.c: remove redundant checking in __delayacct_add_tsk() 2013-11-13 12:09:12 +09:00
dma.c
elfcore.c switch elf_core_write_extra_phdrs() to dump_emit() 2013-11-09 00:16:23 -05:00
exec_domain.c
exit.c introduce for_each_thread() to replace the buggy while_each_thread() 2014-01-21 16:19:46 -08:00
extable.c kernel/extable: fix address-checks for core_kernel and init areas 2013-11-28 09:49:41 -08:00
fork.c exec: kill task_struct->did_exec 2014-01-23 16:37:02 -08:00
freezer.c libata, freezer: avoid block device removal while system is frozen 2013-12-19 13:50:32 -05:00
futex_compat.c
futex.c Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-01-20 10:42:08 -08:00
groups.c userns: Kill nsown_capable it makes the wrong thing easy 2013-08-30 23:44:11 -07:00
hrtimer.c sched/deadline: Add SCHED_DEADLINE structures & implementation 2014-01-13 13:41:06 +01:00
hung_task.c hung_task: Display every hung task warning 2014-01-25 12:13:33 +01:00
irq_work.c
itimer.c
jump_label.c static_key: WARN on usage before jump_label_init was called 2013-10-19 19:45:35 -04:00
kallsyms.c
kcmp.c
Kconfig.freezer
Kconfig.hz kernel: remove CONFIG_USE_GENERIC_SMP_HELPERS 2013-11-15 09:32:22 +09:00
Kconfig.locks
Kconfig.preempt
kexec.c kernel/kexec.c: use vscnprintf() instead of vsnprintf() in vmcoreinfo_append_str() 2014-01-27 21:02:40 -08:00
kmod.c execve: use 'struct filename *' for executable name passing 2014-02-05 12:54:53 -08:00
kprobes.c kprobes: use KSYM_NAME_LEN to size identifier buffers 2013-11-13 12:09:26 +09:00
ksysfs.c rcu: Fix sparse warning for rcu_expedited from kernel/ksysfs.c 2014-02-26 06:35:16 -08:00
kthread.c kthread: make kthread_create() killable 2013-11-13 12:08:59 +09:00
latencytop.c
Makefile rcutorture: Abstract rcu_torture_random() 2014-02-23 09:00:58 -08:00
module_signing.c keys: change asymmetric keys to use common hash definitions 2013-10-25 17:15:18 -04:00
module-internal.h KEYS: Separate the kernel signature checking keyring from module signing 2013-09-25 17:17:01 +01:00
module.c module: Add missing newline in printk call. 2014-01-21 09:59:16 +10:30
notifier.c notifier: Substitute rcu_access_pointer() for rcu_dereference_raw() 2014-02-26 06:35:13 -08:00
nsproxy.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2013-09-07 14:35:32 -07:00
padata.c padata: Fix wrong usage of rcu_dereference() 2013-12-05 21:28:42 +08:00
panic.c panic: Make panic_timeout configurable 2013-11-26 12:12:26 +01:00
params.c params: improve standard definitions 2013-12-04 14:09:46 +10:30
pid_namespace.c pid_namespace: make freeing struct pid_namespace rcu-delayed 2013-10-24 23:43:29 -04:00
pid.c pidns: fix free_pid() to handle the first fork failure 2013-09-30 14:31:03 -07:00
posix-cpu-timers.c posix-timers: Convert abuses of BUG_ON to WARN_ON 2013-12-09 16:56:29 +01:00
posix-timers.c
profile.c
ptrace.c exec/ptrace: fix get_dumpable() incorrect tests 2013-11-13 12:09:33 +09:00
range.c
reboot.c kexec: migrate to reboot cpu 2013-12-18 19:04:50 -08:00
relay.c
res_counter.c memcg: reduce function dereference 2013-09-12 15:38:02 -07:00
resource.c
seccomp.c
signal.c kernel/signal.c: change do_signal_stop/do_sigaction to use while_each_thread() 2014-01-23 16:37:02 -08:00
smp.c kernel/smp.c: remove cpumask_ipi 2014-01-30 16:56:54 -08:00
smpboot.c
smpboot.h
softirq.c Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-01-31 09:02:51 -08:00
stacktrace.c
stop_machine.c stop_machine: Fix race between stop_two_cpus() and stop_cpus() 2013-11-11 12:43:38 +01:00
sys_ni.c
sys.c kernel/sys.c: k_getrusage() can use while_each_thread() 2014-01-23 16:37:02 -08:00
sysctl_binary.c kernel/sysctl_binary.c: use scnprintf() instead of snprintf() 2013-11-13 12:09:33 +09:00
sysctl.c Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-01-31 08:59:46 -08:00
system_certificates.S KEYS: correct alignment of system_certificate_list content in assembly file 2013-12-10 18:25:28 +00:00
system_keyring.c KEYS: correct alignment of system_certificate_list content in assembly file 2013-12-10 18:25:28 +00:00
task_work.c task_work: documentation 2013-09-11 15:58:27 -07:00
taskstats.c genetlink: only pass array to genl_register_family_with_ops() 2013-11-19 16:39:05 -05:00
test_kprobes.c
time.c
timeconst.bc
timer.c timer: Convert kmalloc_node(...GFP_ZERO...) to kzalloc_node(...) 2013-11-19 14:59:50 +01:00
torture.c rcutorture: Gracefully handle NULL cleanup hooks 2014-02-23 09:04:39 -08:00
tracepoint.c
tsacct.c
uid16.c userns: Kill nsown_capable it makes the wrong thing easy 2013-08-30 23:44:11 -07:00
up.c kernel: provide a __smp_call_function_single stub for !CONFIG_SMP 2013-11-15 09:32:22 +09:00
user_namespace.c KEYS: Add per-user_namespace registers for persistent per-UID kerberos caches 2013-09-24 10:35:19 +01:00
user-return-notifier.c
user.c KEYS: fix uninitialized persistent_keyring_register_sem 2013-12-13 15:59:11 +00:00
utsname_sysctl.c
utsname.c userns: Kill nsown_capable it makes the wrong thing easy 2013-08-30 23:44:11 -07:00
watchdog.c watchdog: update watchdog_thresh properly 2013-09-24 17:00:25 -07:00
workqueue_internal.h
workqueue.c Merge branch 'for-3.14' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq 2014-01-21 17:46:31 -08:00