Messages in this thread Patch in this message | | | From | paulmck@kernel ... | Subject | [PATCH tip/core/rcu 3/6] rcu: Don't set nesting depth negative in rcu_preempt_deferred_qs() | Date | Wed, 15 Apr 2020 10:56:11 -0700 |
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From: Lai Jiangshan <laijs@linux.alibaba.com>
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 therfore removes this recursion-protection code from rcu_preempt_deferred_qs().
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> [ paulmck: Fix typo in commit log per Steve Rostedt. ] --- kernel/rcu/tree_plugin.h | 5 ----- 1 file changed, 5 deletions(-)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index ccad776..263c766 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); } /* -- 2.9.5
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