Re: [PATCH v3 07/26] xprtrdma: Improve locking around rpcrdma_rep destruction

[Trond Myklebust <trondmy@hammerspace.com>]

On Mon, 2021-04-19 at 14:02 -0400, Chuck Lever wrote:
> Currently rpcrdma_reps_destroy() assumes that, at transport
> tear-down, the content of the rb_free_reps list is the same as the
> content of the rb_all_reps list. Although that is usually true,
> using the rb_all_reps list should be more reliable because of
> the way it's managed. And, rpcrdma_reps_unmap() uses rb_all_reps;
> these two functions should both traverse the "all" list.
> 
> Ensure that all rpcrdma_reps are always destroyed whether they are
> on the rep free list or not.
> 
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  net/sunrpc/xprtrdma/verbs.c |   31 ++++++++++++++++++++++++-------
>  1 file changed, 24 insertions(+), 7 deletions(-)
> 
> diff --git a/net/sunrpc/xprtrdma/verbs.c
> b/net/sunrpc/xprtrdma/verbs.c
> index 1b599a623eea..482fdc9e25c2 100644
> --- a/net/sunrpc/xprtrdma/verbs.c
> +++ b/net/sunrpc/xprtrdma/verbs.c
> @@ -1007,16 +1007,23 @@ struct rpcrdma_rep *rpcrdma_rep_create(struct
> rpcrdma_xprt *r_xprt,
>         return NULL;
>  }
>  
> -/* No locking needed here. This function is invoked only by the
> - * Receive completion handler, or during transport shutdown.
> - */
> -static void rpcrdma_rep_destroy(struct rpcrdma_rep *rep)
> +static void rpcrdma_rep_destroy_locked(struct rpcrdma_rep *rep)

The name here is extremely confusing. As far as I can tell, this isn't
called with any lock?

>  {
> -       list_del(&rep->rr_all);
>         rpcrdma_regbuf_free(rep->rr_rdmabuf);
>         kfree(rep);
>  }
>  
> +static void rpcrdma_rep_destroy(struct rpcrdma_rep *rep)
> +{
> +       struct rpcrdma_buffer *buf = &rep->rr_rxprt->rx_buf;
> +
> +       spin_lock(&buf->rb_lock);
> +       list_del(&rep->rr_all);
> +       spin_unlock(&buf->rb_lock);
> +
> +       rpcrdma_rep_destroy_locked(rep);
> +}
> +
>  static struct rpcrdma_rep *rpcrdma_rep_get_locked(struct
> rpcrdma_buffer *buf)
>  {
>         struct llist_node *node;
> @@ -1049,8 +1056,18 @@ static void rpcrdma_reps_destroy(struct
> rpcrdma_buffer *buf)
>  {
>         struct rpcrdma_rep *rep;
>  
> -       while ((rep = rpcrdma_rep_get_locked(buf)) != NULL)
> -               rpcrdma_rep_destroy(rep);
> +       spin_lock(&buf->rb_lock);
> +       while ((rep = list_first_entry_or_null(&buf->rb_all_reps,
> +                                              struct rpcrdma_rep,
> +                                              rr_all)) != NULL) {
> +               list_del(&rep->rr_all);
> +               spin_unlock(&buf->rb_lock);
> +
> +               rpcrdma_rep_destroy_locked(rep);
> +
> +               spin_lock(&buf->rb_lock);
> +       }
> +       spin_unlock(&buf->rb_lock);
>  }
>  
>  /**
> 
> 

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com