From ff51ff84d82aea5a889b85f2b9fb3aa2b8691668 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 1 Oct 2019 11:18:37 +0200 Subject: sched/core: Avoid spurious lock dependencies While seemingly harmless, __sched_fork() does hrtimer_init(), which, when DEBUG_OBJETS, can end up doing allocations. This then results in the following lock order: rq->lock zone->lock.rlock batched_entropy_u64.lock Which in turn causes deadlocks when we do wakeups while holding that batched_entropy lock -- as the random code does. Solve this by moving __sched_fork() out from under rq->lock. This is safe because nothing there relies on rq->lock, as also evident from the other __sched_fork() callsite. Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Qian Cai Cc: Thomas Gleixner Cc: akpm@linux-foundation.org Cc: bigeasy@linutronix.de Cc: cl@linux.com Cc: keescook@chromium.org Cc: penberg@kernel.org Cc: rientjes@google.com Cc: thgarnie@google.com Cc: tytso@mit.edu Cc: will@kernel.org Fixes: b7d5dc21072c ("random: add a spinlock_t to struct batched_entropy") Link: https://lkml.kernel.org/r/20191001091837.GK4536@hirez.programming.kicks-ass.net Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 0f2eb3629070..33cd25051f3a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6019,10 +6019,11 @@ void init_idle(struct task_struct *idle, int cpu) struct rq *rq = cpu_rq(cpu); unsigned long flags; + __sched_fork(0, idle); + raw_spin_lock_irqsave(&idle->pi_lock, flags); raw_spin_lock(&rq->lock); - __sched_fork(0, idle); idle->state = TASK_RUNNING; idle->se.exec_start = sched_clock(); idle->flags |= PF_IDLE; -- cgit