linux/kernel/rcu
Paul E. McKenney 7ec99de36f rcu: Provide exact CPU-online tracking for RCU
Up to now, RCU has assumed that the CPU-online process makes it from
CPU_UP_PREPARE to set_cpu_online() within one jiffy.  Given the recent
rise of virtualized environments, this assumption is very clearly
obsolete.  Failing to meet this deadline can result in RCU paying
attention to an incoming CPU for one jiffy, then ignoring it until the
grace period following the one in which that CPU sets itself online.
This situation might prove to be fatally disappointing to any RCU
read-side critical sections that had the misfortune to execute during
the time in which RCU was ignoring the slow-to-come-online CPU.

This commit therefore updates RCU's internal CPU state-tracking
information at notify_cpu_starting() time, thus providing RCU with
an exact transition of the CPU's state from offline to online.

Note that this means that incoming CPUs must not use RCU read-side
critical section (other than those of SRCU) until notify_cpu_starting()
time.  Note also that the CPU_STARTING notifiers -are- allowed to use
RCU read-side critical sections.  (Of course, CPU-hotplug notifiers are
rapidly becoming obsolete, so you need to act fast!)

If a given architecture or CPU family needs to use RCU read-side
critical sections earlier, the call to rcu_cpu_starting() from
notify_cpu_starting() will need to be architecture-specific, with
architectures that need early use being required to hand-place
the call to rcu_cpu_starting() at some point preceding the call to
notify_cpu_starting().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-08-22 09:36:57 -07:00
..
Makefile rcutorture: Add RCU grace-period performance tests 2016-03-31 13:37:38 -07:00
rcu.h tiny_rcu: Directly force QS when call_rcu_[bh|sched]() on idle_task 2015-01-06 11:01:12 -08:00
rcuperf.c rcutorture: Fix error return code in rcu_perf_init() 2016-06-14 16:03:32 -07:00
rcutorture.c Merge branches 'doc.2016.06.15a', 'fixes.2016.06.15b' and 'torture.2016.06.14a' into HEAD 2016-06-15 16:58:03 -07:00
srcu.c rcu: Add rcu_normal kernel parameter to suppress expediting 2015-12-04 12:26:53 -08:00
sync.c rcu_sync: Cleanup the CONFIG_PROVE_RCU checks 2015-10-06 11:25:45 -07:00
tiny_plugin.h rcu: Make rcu/tiny_plugin.h explicitly non-modular 2016-02-23 19:59:55 -08:00
tiny.c rcu: Use rcu_callback_t in call_rcu*() and friends 2015-10-06 11:08:05 -07:00
tree_exp.h Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-07-25 12:41:29 -07:00
tree_plugin.h Merge branches 'doc.2016.06.15a', 'fixes.2016.06.15b' and 'torture.2016.06.14a' into HEAD 2016-06-15 16:58:03 -07:00
tree_trace.c rcu: Shorten expedited_workdone* to exp_workdone* 2016-03-31 13:34:08 -07:00
tree.c rcu: Provide exact CPU-online tracking for RCU 2016-08-22 09:36:57 -07:00
tree.h rcu: Correctly handle sparse possible cpus 2016-06-15 16:00:05 -07:00
update.c rcu: Make call_rcu_tasks() tolerate first call with irqs disabled 2016-06-15 15:45:00 -07:00