linux-kernel - Re: [PATCH v8 2/2] locking/lockdep: Test no new string literal is created in lockdep_set

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Message-ID: <ZuAVrkMQvk41PNKH@boqun-archlinux>
Date: Tue, 10 Sep 2024 02:47:26 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Ahmed Ehab <bottaawesome633@...il.com>
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>, linux-ext4@...r.kernel.org,
	syzkaller@...glegroups.com
Subject: Re: [PATCH v8 2/2] locking/lockdep: Test no new string literal is
 created in lockdep_set_subclass()

Hi Ahmed,

On Thu, Sep 05, 2024 at 04:12:20AM +0300, Ahmed Ehab wrote:
> Add a test case to ensure that no new name string literal will be
> created in lockdep_set_subclass(), otherwise a warning will be triggered
> in look_up_lock_class(). Add this to catch the problem in the future. 
> 

This overall looks good to me, I'm going to take it and create a PR for
tip in next release. However, please note a few things:

* Since you only send one of the patch from your original series, you
  should avoid use "2/2" in the title, because it could be confusing
  whether there is "1/2" lost in sending. If you want to make sure
  people aware that this is a continued work of the patch #2 in your
  original series, you can put some description after the following
  "---"

* You need also to put changes between patch versions after "---" so
  that people can know the context, for example, I have no idea why you
  send a v8 after v7 and what's the delta here. Here is an example of
  how to document the delta:

  	https://lore.kernel.org/rust-for-linux/20240827-static-mutex-v2-1-17fc32b20332@google.com/

Regards,
Boqun

> Signed-off-by: Ahmed Ehab <bottaawesome633@...il.com>
> ---
>  lib/locking-selftest.c | 40 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
> 
> diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
> index 6f6a5fc85b42..0783ee97c971 100644
> --- a/lib/locking-selftest.c
> +++ b/lib/locking-selftest.c
> @@ -2710,6 +2710,44 @@ static void local_lock_3B(void)
>  
>  }
>  
> +#if CONFIG_DEBUG_LOCK_ALLOC
> +static inline const char *rw_semaphore_lockdep_name(struct rw_semaphore *rwsem)
> +{
> +	return rwsem->dep_map.name;
> +}
> +#else
> +static inline const char *rw_semaphore_lockdep_name(struct rw_semaphore *rwsem)
> +{
> +	return NULL;
> +}
> +#endif
> +
> +static void lock_class_subclass_X1(void)
> +{
> +	const char *name_before_setting_subclass = rw_semaphore_lockdep_name(&rwsem_X1);
> +	const char *name_after_setting_subclass;
> +
> +	lockdep_set_subclass(&rwsem_X1, 1);
> +	name_after_setting_subclass = rw_semaphore_lockdep_name(&rwsem_X1);
> +	DEBUG_LOCKS_WARN_ON(name_before_setting_subclass != name_after_setting_subclass);
> +}
> +
> +/*
> + * after setting the subclass the lockdep_map.name changes
> + * if we initialize a new string literal for the subclass
> + * we will have a new name pointer
> + */
> +static void class_subclass_X1_name_test(void)
> +{
> +	printk("  --------------------------------------------------------------------------\n");
> +	printk("  | class and subclass name test|\n");
> +	printk("  ---------------------\n");
> +
> +	print_testname("lock class and subclass same name");
> +	dotest(lock_class_subclass_X1, SUCCESS, LOCKTYPE_RWSEM);
> +	pr_cont("\n");
> +}
> +
>  static void local_lock_tests(void)
>  {
>  	printk("  --------------------------------------------------------------------------\n");
> @@ -2920,6 +2958,8 @@ void locking_selftest(void)
>  	dotest(hardirq_deadlock_softirq_not_deadlock, FAILURE, LOCKTYPE_SPECIAL);
>  	pr_cont("\n");
>  
> +	class_subclass_X1_name_test();
> +
>  	if (unexpected_testcase_failures) {
>  		printk("-----------------------------------------------------------------\n");
>  		debug_locks = 0;
> -- 
> 2.46.0
>