Re: [PATCH] usb: roles: Fix a false positive recursive locking complaint

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Hi Bart,

On 9/4/24 2:15 PM, Bart Van Assche wrote:
On 9/4/24 2:00 PM, Badhri Jagan Sridharan wrote:
https://lore.kernel.org/all/ZsiYRAJST%2F2hAju1@xxxxxxxxxxxxxxxxx/ was
already accepted

Thanks, I hadn't noticed this yet.

and is perhaps better than what you are suggesting as
it does not use the internal methods of mutex_init().

Although I do not have a strong opinion about which patch is sent to
Linus, I think my patch has multiple advantages compared to the patch
mentioned above:
- Cleaner. lockdep_set_class() is not used. Hence, it is not possible
  that the wrong lockdep key is used (the one assigned by
  mutex_init()).
- The lock_class_key declaration occurs close to the sw->lock
  declaration.
- The lockdep_register_key() call occurs close to __mutex_init() call
  that uses the registered key.
- Needs less memory in debug kernels. The advantage of __mutex_init()
  compared to mutex_init() is that it does not allocate (static) memory
  for a lockdep key.

Thanks for the patch.

While I agree on (1) & (4), *may* be a good reason to reconsider.
However, I have seen almost 30+ instances of the prior
method (https://lore.kernel.org/all/20240822223717.253433-1-amitsd@xxxxxxxxxx/)
of registering lockdep key, which is what I followed.
However, if that's is not the right way, it brings into question the purpose
of lockdep_set_class() considering I would always and unconditionally use
__mutex_init()  if I want to manage the lockdep class keys myself or
mutex_init() if I didn't.


Thanks,

Amit

Thanks,

Bart.





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