On Wed, Aug 13, 2025 at 09:30:02PM +0800, Zqiang wrote:
> Currently, the per-cpu rcu_data structure's->defer_qs_iw is initialized by
> IRQ_WORK_INIT_HARD(), this means the rcu_preempt_deferred_qs_handler()
> always be executed in the hardirq context of irq-disabled.
> This commit therefore remove local_irq_save/restore() operations in
> rcu_preempt_deferred_qs_handler() and add lockdep_assert_irqs_disabled()
> check, if someone mistakenly invokes this function in hardirq enabled
> context will splat.
>
> Signed-off-by: Zqiang <[email protected]>
Queued for further review and testing. With luck, this will make the
v6.18 merge window. I could not resist editing the commit log, so could
you please check whether I messed something up?
Thanx, Paul
------------------------------------------------------------------------
commit 523e71ba3007f8f7c260b9c2baf69c9461a84f55
Author: Zqiang <[email protected]>
Date: Wed Aug 13 21:30:02 2025 +0800
rcu: Remove local_irq_save/restore() in rcu_preempt_deferred_qs_handler()
The per-CPU rcu_data structure's ->defer_qs_iw field is initialized
by IRQ_WORK_INIT_HARD(), which means that the subsequent invocation of
rcu_preempt_deferred_qs_handler() will always be executed with interrupts
disabled. This commit therefore removes the local_irq_save/restore()
operations from rcu_preempt_deferred_qs_handler() and adds a call to
lockdep_assert_irqs_disabled() in order to enable lockdep to diagnose
mistaken invocations of this function from interrupts-enabled code.
Signed-off-by: Zqiang <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index fc14adf15cbb34..57e2ae51c0b2cb 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -626,11 +626,10 @@ notrace void rcu_preempt_deferred_qs(struct task_struct
*t)
*/
static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
{
- unsigned long flags;
struct rcu_data *rdp;
+ lockdep_assert_irqs_disabled();
rdp = container_of(iwp, struct rcu_data, defer_qs_iw);
- local_irq_save(flags);
/*
* If the IRQ work handler happens to run in the middle of RCU read-side
@@ -647,8 +646,6 @@ static void rcu_preempt_deferred_qs_handler(struct irq_work
*iwp)
*/
if (rcu_preempt_depth() > 0)
WRITE_ONCE(rdp->defer_qs_iw_pending, DEFER_QS_IDLE);
-
- local_irq_restore(flags);
}
/*
