Re: [PATCH for-next v15 2/2] RDMA/rxe: Convert read side locking to rcu

[Jason Gunthorpe <jgg@nvidia.com>]

On Mon, Jun 06, 2022 at 09:18:04AM -0500, Bob Pearson wrote:
> Use rcu_read_lock() for protecting read side operations in rxe_pool.c.
> 
> Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
>  drivers/infiniband/sw/rxe/rxe_pool.c | 26 ++++++++++----------------
>  1 file changed, 10 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/infiniband/sw/rxe/rxe_pool.c b/drivers/infiniband/sw/rxe/rxe_pool.c
> index 7a5685f0713e..103bf0c03441 100644
> +++ b/drivers/infiniband/sw/rxe/rxe_pool.c
> @@ -195,16 +195,15 @@ void *rxe_pool_get_index(struct rxe_pool *pool, u32 index)
>  {
>  	struct rxe_pool_elem *elem;
>  	struct xarray *xa = &pool->xa;
> -	unsigned long flags;
>  	void *obj;
>  
> -	xa_lock_irqsave(xa, flags);
> +	rcu_read_lock();
>  	elem = xa_load(xa, index);
>  	if (elem && kref_get_unless_zero(&elem->ref_cnt))
>  		obj = elem->obj;
>  	else
>  		obj = NULL;
> -	xa_unlock_irqrestore(xa, flags);
> +	rcu_read_unlock();
>  
>  	return obj;
>  }
> @@ -221,16 +220,15 @@ int __rxe_cleanup(struct rxe_pool_elem *elem, bool sleepable)
>  	struct rxe_pool *pool = elem->pool;
>  	struct xarray *xa = &pool->xa;
>  	static int timeout = RXE_POOL_TIMEOUT;
> -	unsigned long flags;
>  	int ret, err = 0;
>  	void *xa_ret;
>  
> +	WARN_ON(!in_task());

I think this should just be

if (sleepable)
    might_sleep();


?

It all seems OK, any chance the AH bit can be split to its own patch
or is it all interconnected? It would be easier for rc this way.

Jason