From c546951d9c9300065bad253ecdf1ac59ce9d06c8 Mon Sep 17 00:00:00 2001 From: Andrea Parri Date: Mon, 21 Jan 2019 16:52:40 +0100 Subject: sched/core: Use READ_ONCE()/WRITE_ONCE() in move_queued_task()/task_rq_lock() move_queued_task() synchronizes with task_rq_lock() as follows: move_queued_task() task_rq_lock() [S] ->on_rq = MIGRATING [L] rq = task_rq() WMB (__set_task_cpu()) ACQUIRE (rq->lock); [S] ->cpu = new_cpu [L] ->on_rq where "[L] rq = task_rq()" is ordered before "ACQUIRE (rq->lock)" by an address dependency and, in turn, "ACQUIRE (rq->lock)" is ordered before "[L] ->on_rq" by the ACQUIRE itself. Use READ_ONCE() to load ->cpu in task_rq() (c.f., task_cpu()) to honor this address dependency. Also, mark the accesses to ->cpu and ->on_rq with READ_ONCE()/WRITE_ONCE() to comply with the LKMM. Signed-off-by: Andrea Parri Signed-off-by: Peter Zijlstra (Intel) Cc: Alan Stern Cc: Linus Torvalds Cc: Mike Galbraith Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Will Deacon Link: https://lkml.kernel.org/r/20190121155240.27173-1-andrea.parri@amarulasolutions.com Signed-off-by: Ingo Molnar --- kernel/sched/sched.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'kernel/sched/sched.h') diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 99e2a7772d16..c688ef5012e5 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1479,9 +1479,9 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu) */ smp_wmb(); #ifdef CONFIG_THREAD_INFO_IN_TASK - p->cpu = cpu; + WRITE_ONCE(p->cpu, cpu); #else - task_thread_info(p)->cpu = cpu; + WRITE_ONCE(task_thread_info(p)->cpu, cpu); #endif p->wake_cpu = cpu; #endif @@ -1582,7 +1582,7 @@ static inline int task_on_rq_queued(struct task_struct *p) static inline int task_on_rq_migrating(struct task_struct *p) { - return p->on_rq == TASK_ON_RQ_MIGRATING; + return READ_ONCE(p->on_rq) == TASK_ON_RQ_MIGRATING; } /* -- cgit v1.2.3