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[ Upstream commit 3940f5349b476197fb079c5aa19c9a988de64efb ]
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
Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.