Re: [PATCH net] rhashtable: fix sparse RCU warnings on bit lock in bucket pointer

[NeilBrown <neilb@suse.com>]

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On Wed, May 15 2019, Jakub Kicinski wrote:

> Since the bit_spin_lock() operations don't actually dereference
> the pointer, it's fine to forcefully drop the RCU annotation.
> This fixes 7 sparse warnings per include site.
>
> Fixes: 8f0db018006a ("rhashtable: use bit_spin_locks to protect hash bucket.")
> Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
> Reviewed-by: Simon Horman <simon.horman@netronome.com>

Hi, sorry for not responding to your initial post, but I'm otherwise
engaged this week and cannot give it any real time.  I don't object to
this patch, but I'll try to have a proper look next week, if only to
find out how I didn't get the warnings, as I was testing with sparse.

Thanks,
NeilBrown


> ---
>  include/linux/rhashtable.h | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
> index f7714d3b46bd..bea1e0440ab4 100644
> --- a/include/linux/rhashtable.h
> +++ b/include/linux/rhashtable.h
> @@ -325,27 +325,27 @@ static inline struct rhash_lock_head __rcu **rht_bucket_insert(
>   */
>  
>  static inline void rht_lock(struct bucket_table *tbl,
> -			    struct rhash_lock_head **bkt)
> +			    struct rhash_lock_head __rcu **bkt)
>  {
>  	local_bh_disable();
> -	bit_spin_lock(0, (unsigned long *)bkt);
> +	bit_spin_lock(0, (unsigned long __force *)bkt);
>  	lock_map_acquire(&tbl->dep_map);
>  }
>  
>  static inline void rht_lock_nested(struct bucket_table *tbl,
> -				   struct rhash_lock_head **bucket,
> +				   struct rhash_lock_head __rcu **bkt,
>  				   unsigned int subclass)
>  {
>  	local_bh_disable();
> -	bit_spin_lock(0, (unsigned long *)bucket);
> +	bit_spin_lock(0, (unsigned long __force *)bkt);
>  	lock_acquire_exclusive(&tbl->dep_map, subclass, 0, NULL, _THIS_IP_);
>  }
>  
>  static inline void rht_unlock(struct bucket_table *tbl,
> -			      struct rhash_lock_head **bkt)
> +			      struct rhash_lock_head __rcu **bkt)
>  {
>  	lock_map_release(&tbl->dep_map);
> -	bit_spin_unlock(0, (unsigned long *)bkt);
> +	bit_spin_unlock(0, (unsigned long __force *)bkt);
>  	local_bh_enable();
>  }
>  
> -- 
> 2.21.0

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