linux-kernel - Re: drivers/input/keyboard/applespi.c:1833 applespi_drain

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Message-ID: <ZoLj2LL0NzdS1gZL@google.com>
Date: Mon, 1 Jul 2024 10:14:00 -0700
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: oe-kbuild@...ts.linux.dev,
	Ronald Tschalär <ronald@...ovation.ch>,
	lkp@...el.com, oe-kbuild-all@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: drivers/input/keyboard/applespi.c:1833 applespi_drain_writes()
 warn: mixing irqsave and irq

Hi Dan,

On Mon, Jul 01, 2024 at 06:30:38PM +0200, Dan Carpenter wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   6d6444ba82053c716fb5ac83346202659023044e
> commit: 038b1a05eae6666b731920e46f47d8e2332e07ff Input: add Apple SPI keyboard and trackpad driver
> config: x86_64-randconfig-161-20240628 (https://download.01.org/0day-ci/archive/20240628/202406280337.1Av9qm8V-lkp@intel.com/config)
> compiler: clang version 18.1.5 (https://github.com/llvm/llvm-project 617a15a9eac96088ae5e9134248d8236e34b91b1)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> | Closes: https://lore.kernel.org/r/202406280337.1Av9qm8V-lkp@intel.com/
> 
> smatch warnings:
> drivers/input/keyboard/applespi.c:1833 applespi_drain_writes() warn: mixing irqsave and irq
> drivers/input/keyboard/applespi.c:1845 applespi_drain_reads() warn: mixing irqsave and irq
> 
> vim +1833 drivers/input/keyboard/applespi.c
> 
> 038b1a05eae666 Ronald Tschalär 2019-07-15  1826  static void applespi_drain_writes(struct applespi_data *applespi)
> 038b1a05eae666 Ronald Tschalär 2019-07-15  1827  {
> 038b1a05eae666 Ronald Tschalär 2019-07-15  1828  	unsigned long flags;
> 038b1a05eae666 Ronald Tschalär 2019-07-15  1829  
> 038b1a05eae666 Ronald Tschalär 2019-07-15  1830  	spin_lock_irqsave(&applespi->cmd_msg_lock, flags);
> 
> _irqsave() sort of implies that potentially the caller has disabled IRQs,
> otherwise we would use spin_lock_irq() if we knew they hadn't disabled
> IRQs.
> 
> 038b1a05eae666 Ronald Tschalär 2019-07-15  1831  
> 038b1a05eae666 Ronald Tschalär 2019-07-15  1832  	applespi->drain = true;
> 038b1a05eae666 Ronald Tschalär 2019-07-15 @1833  	wait_event_lock_irq(applespi->drain_complete, !applespi->write_active,
> 038b1a05eae666 Ronald Tschalär 2019-07-15  1834  			    applespi->cmd_msg_lock);
> 
> This will renable IRQs briefly and then disable them again.
> 
> 038b1a05eae666 Ronald Tschalär 2019-07-15  1835  
> 038b1a05eae666 Ronald Tschalär 2019-07-15  1836  	spin_unlock_irqrestore(&applespi->cmd_msg_lock, flags);
> 
> This will set them back to how they were at the start of the function.
> 
> The issue is that if the caller really wanted IRQs disabled, then it's
> not necessarilly a good idea to enable them at all in the
> wait_event_lock_irq() macro.  I suspect that in real life no callers
> disable IRQs so it's not an issue.  But anyway, that's what the warning
> is about.

applespi_drain_writes() and applespi_drain_reads() are only called from
the process context with interrupts enabled, so it looks like we should
simply change spin_lock_irqsave() to spin_lock_irq().

I am taking patches ;)

Thanks.

-- 
Dmitry