From: Lai Jiangshan Date: Sat, 15 Feb 2020 22:37:26 +0000 (-0800) Subject: rcu: Don't set nesting depth negative in rcu_preempt_deferred_qs() X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=07b4a930fc44a537efecf73c1fd2b4937f64caaa;p=linux.git 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: Lai Jiangshan Signed-off-by: Paul E. McKenney --- diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index ccad77639d800..263c766b9dc1a 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -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); } /*