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rcu: Fix stall-warning deadlock due to non-release of rcu_node ->lock

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[ 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: c583bcb8f5 ("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>
This commit is contained in:
Yanfei Xu 2021-05-16 17:50:10 +08:00 committed by Greg Kroah-Hartman
parent ea5e5bc881
commit 497f3d9c3f
1 changed files with 3 additions and 1 deletions
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4
kernel/rcu/tree_stall.h
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@ -263,8 +263,10 @@ 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,