Commit 07b4a930 authored by Lai Jiangshan's avatar Lai Jiangshan Committed by Paul E. McKenney
Browse files

rcu: Don't set nesting depth negative in rcu_preempt_deferred_qs() 



Now that RCU flavors have been consolidated, an RCU-preempt
rcu_read_unlock() in an interrupt or softirq handler cannot possibly
end the RCU read-side critical section.  Consider the old vulnerability
involving rcu_preempt_deferred_qs() being invoked within such a handler
that interrupted an extended RCU read-side critical section, in which
a wakeup might be invoked with a scheduler lock held.  Because
rcu_read_unlock_special() no longer does wakeups in such situations,
it is no longer necessary for rcu_preempt_deferred_qs() to set the
nesting level negative.

This commit therefore removes this recursion-protection code from
rcu_preempt_deferred_qs().

[ paulmck: Fix typo in commit log per Steve Rostedt. ]
Signed-off-by: default avatarLai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent e4453d8a

kernel/rcu/tree_plugin.h

+0 −5
Original line number Diff line number Diff line
@@ -569,16 +569,11 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t) 
static void rcu_preempt_deferred_qs(struct task_struct *t)

{

	unsigned long flags;

	bool couldrecurse = rcu_preempt_depth() >= 0;



	if (!rcu_preempt_need_deferred_qs(t))

		return;

	if (couldrecurse)

		rcu_preempt_depth_set(rcu_preempt_depth() - RCU_NEST_BIAS);

	local_irq_save(flags);

	rcu_preempt_deferred_qs_irqrestore(t, flags);

	if (couldrecurse)

		rcu_preempt_depth_set(rcu_preempt_depth() + RCU_NEST_BIAS);

}



/*