From: Yanfei Xu yanfei.xu@windriver.com
[ Upstream commit dc87740c8a6806bd2162bfb441770e4e53be5601 ]
If rcu_print_task_stall() is invoked on an rcu_node structure that does not contain any tasks blocking the current grace period, it takes an early exit that fails to release that rcu_node structure's lock. This results in a self-deadlock, which is detected by lockdep.
To reproduce this bug:
tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 3 --trust-make --configs "TREE03" --kconfig "CONFIG_PROVE_LOCKING=y" --bootargs "rcutorture.stall_cpu=30 rcutorture.stall_cpu_block=1 rcutorture.fwd_progress=0 rcutorture.test_boost=0"
This will also result in other complaints, including RCU's scheduler hook complaining about blocking rather than preemption and an rcutorture writer stall.
Only a partial RCU CPU stall warning message will be printed because of the self-deadlock.
This commit therefore releases the lock on the rcu_print_task_stall() function's early exit path.
Fixes: c583bcb8f5ed ("rcu: Don't invoke try_invoke_on_locked_down_task() with irqs disabled") Tested-by: Qais Yousef qais.yousef@arm.com Signed-off-by: Yanfei Xu yanfei.xu@windriver.com Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 f1e011d4a899..c615fd153cb2 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -269,8 +269,10 @@ static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags) struct task_struct *ts[8];
lockdep_assert_irqs_disabled(); - 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,