>From 44b530f4bb9c94ae4e429b83d730237f11410a5f Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Wed, 29 Apr 2020 09:40:46 +0200 Subject: [PATCH] xen/sched: allow rcu work to happen when syncing cpus in core scheduling With RCU barriers moved from tasklets to normal RCU processing cpu offlining in core scheduling might deadlock due to cpu synchronization required by RCU processing and core scheduling concurrently. Fix that by bailing out from core scheduling synchronization in case of pending RCU work. Additionally the RCU softirq is now required to be of higher priority than the scheduling softirqs in order to do RCU processing before entering the scheduler again, as bailing out from the core scheduling synchronization requires to raise another softirq SCHED_SLAVE, which would bypass RCU processing again. Reported-by: Sergey Dyasli Signed-off-by: Juergen Gross --- xen/common/sched/core.c | 10 +++++++--- xen/include/xen/softirq.h | 2 +- 2 files changed, 8 insertions(+), 4 deletions(-) diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c index d94b95285f..a099e37b0f 100644 --- a/xen/common/sched/core.c +++ b/xen/common/sched/core.c @@ -2457,13 +2457,17 @@ static struct sched_unit *sched_wait_rendezvous_in(struct sched_unit *prev, v = unit2vcpu_cpu(prev, cpu); } /* - * Coming from idle might need to do tasklet work. + * Check for any work to be done which might need cpu synchronization. + * This is either pending RCU work, or tasklet work when coming from + * idle. * In order to avoid deadlocks we can't do that here, but have to - * continue the idle loop. + * schedule the previous vcpu again, which will lead to the desired + * processing to be done. * Undo the rendezvous_in_cnt decrement and schedule another call of * sched_slave(). */ - if ( is_idle_unit(prev) && sched_tasklet_check_cpu(cpu) ) + if ( rcu_pending(cpu) || + (is_idle_unit(prev) && sched_tasklet_check_cpu(cpu)) ) { struct vcpu *vprev = current; diff --git a/xen/include/xen/softirq.h b/xen/include/xen/softirq.h index b4724f5c8b..1f6c4783da 100644 --- a/xen/include/xen/softirq.h +++ b/xen/include/xen/softirq.h @@ -4,10 +4,10 @@ /* Low-latency softirqs come first in the following list. */ enum { TIMER_SOFTIRQ = 0, + RCU_SOFTIRQ, SCHED_SLAVE_SOFTIRQ, SCHEDULE_SOFTIRQ, NEW_TLBFLUSH_CLOCK_PERIOD_SOFTIRQ, - RCU_SOFTIRQ, TASKLET_SOFTIRQ, NR_COMMON_SOFTIRQS }; -- 2.16.4