linux-kernel - [PATCH] irq_work: Avoid unnecessary "IRQ work" interrupts

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <25833c44051f02ea2fd95309652628e2b1607a1e.camel@lenze.com>
Date: Tue, 27 Aug 2024 15:45:42 +0000
From: "Brandt, Oliver - Lenze" <oliver.brandt@...ze.com>
To: "bigeasy@...utronix.de" <bigeasy@...utronix.de>
CC: "tglx@...utronix.de" <tglx@...utronix.de>, "peterz@...radead.org"
	<peterz@...radead.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: [PATCH] irq_work: Avoid unnecessary "IRQ work" interrupts

It was noticed that newer kernels (>= 6.1) raises a lot of "IRQ work"
interrupts where older ones (<= 5.10) haven't used this at all on our
system.

Root cause seems to be commit b4c6f86ec2f6 ('irq_work: Handle some
irq_work in a per-CPU thread on PREEMPT_RT'). This commit tries to avoid
calling irq_work callbacks from hardirq context as much as possible.
Therefore interrupts marked as IRQ_WORK_LAZY and (on PREEMT_RT) interrupts
not marked as IRQ_WORK_HARD_IRQ should be handled from an per-CPU thread.

Running the remaining interrupts from hardirq context is triggered using
irq_work_raise(). But on PREEMPT_RT irq_work_raise() will be called for
all interrupts not marked as IRQ_WORK_LAZY which results in unnecessary
"IRQ work" interrupts.

Fixes: b4c6f86ec2f6 ('irq_work: Handle some irq_work in a per-CPU thread on PREEMPT_RT')
Signed-off-by: Oliver Brandt <oliver.brandt@...ze.com>
---
 kernel/irq_work.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 2f4fb336dda1..df08b7dde7d5 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -108,7 +108,7 @@ static void __irq_work_queue_local(struct irq_work *work)
                return;

        /* If the work is "lazy", handle it from next tick if any */
-       if (!lazy_work || tick_nohz_tick_stopped())
+       if (!(lazy_work || rt_lazy_work) || tick_nohz_tick_stopped())
                irq_work_raise(work);
 }

-- 
2.46.0