linux-kernel - Re: [PATCH v2 00/34] Compiler-Based Capability- and Locking-Analysis

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Message-ID: <76f8c8e1-5f32-4f31-a960-9285a15340e3@acm.org>
Date: Wed, 5 Mar 2025 07:27:32 -0800
From: Bart Van Assche <bvanassche@....org>
To: Peter Zijlstra <peterz@...radead.org>, Marco Elver <elver@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>,
 Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
 "Paul E. McKenney" <paulmck@...nel.org>,
 Alexander Potapenko <glider@...gle.com>, Arnd Bergmann <arnd@...db.de>,
 Bill Wendling <morbo@...gle.com>, Boqun Feng <boqun.feng@...il.com>,
 Dmitry Vyukov <dvyukov@...gle.com>, Eric Dumazet <edumazet@...gle.com>,
 Frederic Weisbecker <frederic@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Herbert Xu <herbert@...dor.apana.org.au>, Ingo Molnar <mingo@...nel.org>,
 Jann Horn <jannh@...gle.com>, Jiri Slaby <jirislaby@...nel.org>,
 Joel Fernandes <joel@...lfernandes.org>, Jonathan Corbet <corbet@....net>,
 Josh Triplett <josh@...htriplett.org>, Justin Stitt
 <justinstitt@...gle.com>, Kees Cook <kees@...nel.org>,
 Kentaro Takeda <takedakn@...data.co.jp>, Mark Rutland
 <mark.rutland@....com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Miguel Ojeda <ojeda@...nel.org>, Nathan Chancellor <nathan@...nel.org>,
 Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
 Steven Rostedt <rostedt@...dmis.org>,
 Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
 Thomas Gleixner <tglx@...utronix.de>, Uladzislau Rezki <urezki@...il.com>,
 Waiman Long <longman@...hat.com>, Will Deacon <will@...nel.org>,
 kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
 llvm@...ts.linux.dev, rcu@...r.kernel.org, linux-crypto@...r.kernel.org,
 linux-serial@...r.kernel.org
Subject: Re: [PATCH v2 00/34] Compiler-Based Capability- and Locking-Analysis

On 3/5/25 3:20 AM, Peter Zijlstra wrote:
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 248416ecd01c..d27607d9c2dc 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -945,6 +945,7 @@ static inline unsigned int blk_boundary_sectors_left(sector_t offset,
>    */
>   static inline struct queue_limits
>   queue_limits_start_update(struct request_queue *q)
> +	__acquires(q->limits_lock)
>   {
>   	mutex_lock(&q->limits_lock);
>   	return q->limits;
> @@ -965,6 +966,7 @@ int blk_validate_limits(struct queue_limits *lim);
>    * starting update.
>    */
>   static inline void queue_limits_cancel_update(struct request_queue *q)
> +	__releases(q->limits_lock)
>   {
>   	mutex_unlock(&q->limits_lock);
>   }

The above is incomplete. Here is what I came up with myself:

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 248416ecd01c..0d011270e642 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -945,15 +945,19 @@ static inline unsigned int 
blk_boundary_sectors_left(sector_t offset,
   */
  static inline struct queue_limits
  queue_limits_start_update(struct request_queue *q)
+       ACQUIRE(q->limits_lock)
  {
         mutex_lock(&q->limits_lock);
         return q->limits;
  }
  int queue_limits_commit_update_frozen(struct request_queue *q,
-               struct queue_limits *lim);
+               struct queue_limits *lim)
+       RELEASE(q->limits_lock);
  int queue_limits_commit_update(struct request_queue *q,
-               struct queue_limits *lim);
-int queue_limits_set(struct request_queue *q, struct queue_limits *lim);
+               struct queue_limits *lim)
+       RELEASE(q->limits_lock);
+int queue_limits_set(struct request_queue *q, struct queue_limits *lim)
+       EXCLUDES(q->limits_lock);
  int blk_validate_limits(struct queue_limits *lim);

  /**
@@ -965,6 +969,7 @@ int blk_validate_limits(struct queue_limits *lim);
   * starting update.
   */
  static inline void queue_limits_cancel_update(struct request_queue *q)
+       RELEASE(q->limits_lock)
  {
         mutex_unlock(&q->limits_lock);
  }

> diff --git a/include/linux/device.h b/include/linux/device.h
> index 80a5b3268986..283fb85d96c8 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -1026,21 +1026,25 @@ static inline bool dev_pm_test_driver_flags(struct device *dev, u32 flags)
>   }
>   
>   static inline void device_lock(struct device *dev)
> +	__acquires(dev->mutex)
>   {
>   	mutex_lock(&dev->mutex);
>   }
>   
>   static inline int device_lock_interruptible(struct device *dev)
> +	__cond_acquires(0, dev->mutex)
>   {
>   	return mutex_lock_interruptible(&dev->mutex);
>   }
>   
>   static inline int device_trylock(struct device *dev)
> +	__cond_acquires(true, dev->mutex)
>   {
>   	return mutex_trylock(&dev->mutex);
>   }
>   
>   static inline void device_unlock(struct device *dev)
> +	__releases(dev->mutex)
>   {
>   	mutex_unlock(&dev->mutex);
>   }

I propose to annotate these functions with __no_capability_analysis as a
first step. Review of all callers of these functions in the entire
kernel tree learned me that annotating these functions results in a
significant number of false positives and not to the discovery of any
bugs. The false positives are triggered by conditional locking. An
example of code that triggers false positive thread-safety warnings:

static void ath9k_hif_usb_firmware_fail(struct hif_device_usb *hif_dev)
{
	struct device *dev = &hif_dev->udev->dev;
	struct device *parent = dev->parent;

	complete_all(&hif_dev->fw_done);

	if (parent)
		device_lock(parent);

	device_release_driver(dev);

	if (parent)
		device_unlock(parent);
}

Thanks,

Bart.