[Question] srcu: is it making sense to recursively invoke srcu_read_lock?

From: Hillf Danton <hdanton@sina.com>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Sean Christopherson <seanjc@google.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: [Question] srcu: is it making sense to recursively invoke srcu_read_lock?
Date: Thu, 21 Apr 2022 12:22:11 +0800	[thread overview]
Message-ID: <20220421042211.2433-1-hdanton@sina.com> (raw)

Given rcu_lock_acquire() in srcu_read_lock(),

	iA = srcu_read_lock(foo);
	iB = srcu_read_lock(foo); // not bar
	...
	srcu_read_unlock(foo, iB);
	srcu_read_unlock(foo, iA);

can the call sequence above trigger warning with CONFIG_DEBUG_LOCK_ALLOC enabled?

Does it make sense to add srcu_lock_acquire() in line with rwsem_acquire_read() if
warning is expected but not triggered?

Thanks
Hillf

static inline void rcu_lock_acquire(struct lockdep_map *map)
{
	lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
}

static inline void srcu_lock_acquire(struct lockdep_map *map)
{
	lock_acquire(map, 0, 0, 1, 0, NULL, _THIS_IP_);
}