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srcu: Remove srcu_queue_delayed_work_on()

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srcu_queue_delayed_work_on() disables preemption (and therefore CPU
hotplug in RCU's case) and then checks based on its own accounting if a
CPU is online. If the CPU is online it uses queue_delayed_work_on()
otherwise it fallbacks to queue_delayed_work().
The problem here is that queue_work() on -RT does not work with disabled
preemption.

queue_work_on() works also on an offlined CPU. queue_delayed_work_on()
has the problem that it is possible to program a timer on an offlined
CPU. This timer will fire once the CPU is online again. But until then,
the timer remains programmed and nothing will happen.

Add a local timer which will fire (as requested per delay) on the local
CPU and then enqueue the work on the specific CPU.

RCUtorture testing with SRCU-P for 24h showed no problems.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
This commit is contained in:
Sebastian Andrzej Siewior
2018-12-11 12:12:38 +01:00
committed by Paul E. McKenney
parent c8ca1aa774
commit e81baf4cb1
4 changed files with 27 additions and 45 deletions
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3
include/linux/srcutree.h
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@@ -45,7 +45,8 @@ struct srcu_data {
unsigned long srcu_gp_seq_needed; /* Furthest future GP needed. */
unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */
bool srcu_cblist_invoking; /* Invoking these CBs? */
struct delayed_work work; /* Context for CB invoking. */
struct timer_list delay_work; /* Delay for CB invoking */
struct work_struct work; /* Context for CB invoking. */
struct rcu_head srcu_barrier_head; /* For srcu_barrier() use. */
struct srcu_node *mynode; /* Leaf srcu_node. */
unsigned long grpmask; /* Mask for leaf srcu_node */