Hello Paul E. McKenney,
The patch e2ba0f065aec: "rcu: Diagnostics for grace-period hangs"
from Apr 21, 2018, leads to the following static checker warning:
kernel/rcu/tree.c:2739 rcu_check_gp_start_stall()
error: double lock 'irqsave:flags'
kernel/rcu/tree.c
2726
2727 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2728 j = jiffies;
2729 if (rcu_gp_in_progress(rsp) ||
2730 ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
2731 time_before(j, READ_ONCE(rsp->gp_req_activity) + HZ) ||
2732 time_before(j, READ_ONCE(rsp->gp_activity) + HZ) ||
2733 atomic_read(&warned)) {
2734 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2735 return;
2736 }
2737 /* Hold onto the leaf lock to make others see warned==1. */
2738
2739 raw_spin_lock_irqsave_rcu_node(rnp_root, flags);
Saving irqsave is not nestable. The second save overwrites the first so
that IRQs can't be re-enabled.
2740 j = jiffies;
2741 if (rcu_gp_in_progress(rsp) ||
2742 ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
2743 time_before(j, rsp->gp_req_activity + HZ) ||
2744 time_before(j, rsp->gp_activity + HZ) ||
2745 atomic_xchg(&warned, 1)) {
2746 raw_spin_unlock_irqrestore_rcu_node(rnp_root, flags);
2747 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2748 return;
2749 }
2750 pr_alert("%s: g%ld->%ld gar:%lu ga:%lu f%#x %s->state:%#lx\n",
2751 __func__, (long)READ_ONCE(rsp->gp_seq),
2752 (long)READ_ONCE(rnp_root->gp_seq_needed),
2753 j - rsp->gp_req_activity, j - rsp->gp_activity,
2754 rsp->gp_flags, rsp->name,
2755 rsp->gp_kthread ? rsp->gp_kthread->state : 0x1ffffL);
2756 WARN_ON(1);
2757 raw_spin_unlock_irqrestore_rcu_node(rnp_root, flags);
2758 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2759 }
regards,
dan carpenter
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