The following commit has been merged into the timers/urgent branch of tip:

Commit-ID:     3940f5349b476197fb079c5aa19c9a988de64efb
Gitweb:        https://git.kernel.org/tip/3940f5349b476197fb079c5aa19c9a988de64efb
Author:        Fernando Fernandez Mancera <ffmancera@riseup.net>
AuthorDate:    Tue, 01 Apr 2025 11:23:03 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Fri, 11 Apr 2025 07:28:20 +02:00

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@linutronix.de>
Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/Z-uwd4Bnn7FcCShX@gmail.com
---
 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 80e262b..cb9852a 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);