linux-kernel - [PATCH -v4] x86/i8253: Call clockevent_i8253

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Message-ID: <Z-uwd4Bnn7FcCShX@gmail.com>
Date: Tue, 1 Apr 2025 11:23:03 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Fernando Fernandez Mancera <ffmancera@...eup.net>,
	Thomas Gleixner <tglx@...utronix.de>
Cc: x86@...nel.org, tglx@...utronix.de, linux-kernel@...r.kernel.org,
	dwmw@...zon.co.uk, mhkelley@...look.com
Subject: [PATCH -v4] x86/i8253: Call clockevent_i8253_disable() with
 interrupts disabled

I've cleaned up and simplified the changelog, see the patch below.

Thomas, does this look good to you too?

Thanks,

	Ingo

=========================>
From: Fernando Fernandez Mancera <ffmancera@...eup.net>
Date: Fri, 28 Mar 2025 00:43:57 +0100
Subject: [PATCH] x86/i8253: Call clockevent_i8253_disable() with interrupts disabled

There's a lockdep false positive warning related to i8253_lock:

  WARNING: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected
  ...
  systemd-sleep/3324 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
  ffffffffb2c23398 (i8253_lock){+.+.}-{2:2}, at: pcspkr_event+0x3f/0xe0 [pcspkr]

  ...
  ... which became HARDIRQ-irq-unsafe at:
  ...
    lock_acquire+0xd0/0x2f0
    _raw_spin_lock+0x30/0x40
    clockevent_i8253_disable+0x1c/0x60
    pit_timer_init+0x25/0x50
    hpet_time_init+0x46/0x50
    x86_late_time_init+0x1b/0x40
    start_kernel+0x962/0xa00
    x86_64_start_reservations+0x24/0x30
    x86_64_start_kernel+0xed/0xf0
    common_startup_64+0x13e/0x141
  ...

Lockdep complains due pit_timer_init() using the lock in an IRQ-unsafe
fashion, but it's a false positive, because there is no deadlock
possible at that point due to init ordering: at the point where
pit_timer_init() is called there is no other possible usage of
i8253_lock because the system is still in the very early boot stage
with no interrupts.

But in any case, pit_timer_init() should disable interrupts before
calling clockevent_i8253_disable() out of general principle, and to
keep lockdep working even in this scenario.

Use scoped_guard() for that, as suggested by Thomas Gleixner.

[ mingo: Cleaned up the changelog. ]

Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Fernando Fernandez Mancera <ffmancera@...eup.net>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/r/20250327234357.3383-1-ffmancera@riseup.net
---
 arch/x86/kernel/i8253.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/i8253.c b/arch/x86/kernel/i8253.c
index 80e262bb627f..cb9852ad6098 100644
--- a/arch/x86/kernel/i8253.c
+++ b/arch/x86/kernel/i8253.c
@@ -46,7 +46,8 @@ bool __init pit_timer_init(void)
 		 * VMMs otherwise steal CPU time just to pointlessly waggle
 		 * the (masked) IRQ.
 		 */
-		clockevent_i8253_disable();
+		scoped_guard(irq)
+			clockevent_i8253_disable();
 		return false;
 	}
 	clockevent_i8253_init(true);