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Subject[PATCH v2] rcu: fix a deadlock caused by not release rcu_node->lock
From: Yanfei Xu <>

rcu_node->lock isn't released in rcu_print_task_stall() if the rcu_node
don't contain tasks which blocking the GP. However this rcu_node->lock
will be used again in rcu_dump_cpu_stacks() soon while the ndetected is
non-zero. As a result the cpu will hung by this deadlock.

Fixes: c583bcb8f5ed ("rcu: Don't invoke try_invoke_on_locked_down_task() with irqs disabled")
Signed-off-by: Yanfei Xu <>
1.change the lock function to unlock function.
2.add fixes tag.

kernel/rcu/tree_stall.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index b72311d24a9f..b09a7140ef77 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -267,8 +267,10 @@ static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags)
struct task_struct *ts[8];

- if (!rcu_preempt_blocked_readers_cgp(rnp))
+ if (!rcu_preempt_blocked_readers_cgp(rnp)) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return 0;
+ }
pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
rnp->level, rnp->grplo, rnp->grphi);
t = list_entry(rnp->gp_tasks->prev,
 \ /
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