linux

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Paul E. McKenney 92aa39e9dc rcu: Make need_resched() respond to urgent RCU-QS needs

The per-CPU rcu_dynticks.rcu_urgent_qs variable communicates an urgent
need for an RCU quiescent state from the force-quiescent-state processing
within the grace-period kthread to context switches and to cond_resched().
Unfortunately, such urgent needs are not communicated to need_resched(),
which is sometimes used to decide when to invoke cond_resched(), for
but one example, within the KVM vcpu_run() function.  As of v4.15, this
can result in synchronize_sched() being delayed by up to ten seconds,
which can be problematic, to say nothing of annoying.

This commit therefore checks rcu_dynticks.rcu_urgent_qs from within
rcu_check_callbacks(), which is invoked from the scheduling-clock
interrupt handler.  If the current task is not an idle task and is
not executing in usermode, a context switch is forced, and either way,
the rcu_dynticks.rcu_urgent_qs variable is set to false.  If the current
task is an idle task, then RCU's dyntick-idle code will detect the
quiescent state, so no further action is required.  Similarly, if the
task is executing in usermode, other code in rcu_check_callbacks() and
its called functions will report the corresponding quiescent state.

Reported-by: Marius Hillenbrand <mhillenb@amazon.de>
Reported-by: David Woodhouse <dwmw2@infradead.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

2018-08-30 16:03:39 -07:00

Kconfig

rcu: Clean up flavor-related definitions and comments in Kconfig

2018-08-30 16:03:32 -07:00

Kconfig.debug

rcu: Move RCU debug Kconfig options to kernel/rcu

2017-06-08 18:52:44 -07:00

Makefile

License cleanup: add SPDX GPL-2.0 license identifier to files with no license

2017-11-02 11:10:55 +01:00

rcu_segcblist.c

rcu: Simplify and inline cpu_needs_another_gp()