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authorPeter Zijlstra <peterz@infradead.org>2019-10-01 11:18:37 +0200
committerIngo Molnar <mingo@kernel.org>2019-11-13 08:01:30 +0100
commitff51ff84d82aea5a889b85f2b9fb3aa2b8691668 (patch)
tree2f5e8e6ff1c9dd57599318f82cad15298c2841b0 /kernel/sched
parent0e3f1ad80fc8cb0c517fd9a9afb22752b741fa76 (diff)
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) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Qian Cai <cai@lca.pw> Cc: Thomas Gleixner <tglx@linutronix.de> 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 <mingo@kernel.org>
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/core.c3
1 files changed, 2 insertions, 1 deletions
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;