[PATCH net-next] net: ethernet: mtk_wed: annotate RCU release in attach()

[Simon Horman]

On Wed, Apr 23, 2025 at 05:08:08PM +0200, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg at intel.com>
> 
> There are some sparse warnings in wifi, and it seems that
> it's actually possible to annotate a function pointer with
> __releases(), making the sparse warnings go away. In a way
> that also serves as documentation that rcu_read_unlock()
> must be called in the attach method, so add that annotation.
> 
> Signed-off-by: Johannes Berg <johannes.berg at intel.com>

Reviewed-by: Simon Horman <horms at kernel.org>

Thinking out loud:

* Without this patch I see the following, but with this patch I do not.

  .../mt7915/mmio.c:636:5: warning: context imbalance in 'mt7915_mmio_wed_init' - wrong count at exit
  .../mt7996/mmio.c:302:5: warning: context imbalance in 'mt7996_mmio_wed_init' - wrong count at exit

* The only implementation of this callback I found is mtk_wed_attach
  which is already annotated as __releases(RCU);

* The only caller of this callback I could find is mtk_wed_device_attach()
  which takes rcu_read_unlock(). And the the callback needs to release it
  to avoid imbalance.