Re: [PATCH v1 1/3] sunrpc: take a xprt offline using sysfs

[Trond Myklebust <trondmy@hammerspace.com>]

On Thu, 2021-06-03 at 18:59 -0400, Olga Kornievskaia wrote:
> From: Olga Kornievskaia <kolga@netapp.com>
> 
> Using sysfs's xprt_state attribute, mark a particular transport
> offline.
> It will not be picked during the round-robin selection. It's not
> allowed
> to take the main (1st created transport associated with the
> rpc_client)
> offline.
> 
> Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
> ---
>  include/linux/sunrpc/xprt.h |  2 ++
>  net/sunrpc/clnt.c           |  1 +
>  net/sunrpc/sysfs.c          | 42 +++++++++++++++++++++++++++++++++--
> --
>  net/sunrpc/xprtmultipath.c  |  3 ++-
>  4 files changed, 43 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/sunrpc/xprt.h
> b/include/linux/sunrpc/xprt.h
> index 13a4eaf385cf..72a858f032c7 100644
> --- a/include/linux/sunrpc/xprt.h
> +++ b/include/linux/sunrpc/xprt.h
> @@ -293,6 +293,7 @@ struct rpc_xprt {
>         struct rcu_head         rcu;
>         const struct xprt_class *xprt_class;
>         struct rpc_sysfs_xprt   *xprt_sysfs;
> +       bool                    main; /* marked if it's the 1st
> transport */
>  };
>  
>  #if defined(CONFIG_SUNRPC_BACKCHANNEL)
> @@ -426,6 +427,7 @@
> void                        xprt_release_write(struct rpc_xprt *,
> struct rpc_task *);
>  #define XPRT_BOUND             (4)
>  #define XPRT_BINDING           (5)
>  #define XPRT_CLOSING           (6)
> +#define XPRT_OFFLINE           (7)
>  #define XPRT_CONGESTED         (9)
>  #define XPRT_CWND_WAIT         (10)
>  #define XPRT_WRITE_SPACE       (11)
> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
> index 9bf820bad84c..408618765aa5 100644
> --- a/net/sunrpc/clnt.c
> +++ b/net/sunrpc/clnt.c
> @@ -412,6 +412,7 @@ static struct rpc_clnt * rpc_new_client(const
> struct rpc_create_args *args,
>         }
>  
>         rpc_clnt_set_transport(clnt, xprt, timeout);
> +       xprt->main = true;
>         xprt_iter_init(&clnt->cl_xpi, xps);
>         xprt_switch_put(xps);
>  
> diff --git a/net/sunrpc/sysfs.c b/net/sunrpc/sysfs.c
> index ec06c9257c07..02c918c5061b 100644
> --- a/net/sunrpc/sysfs.c
> +++ b/net/sunrpc/sysfs.c
> @@ -118,7 +118,7 @@ static ssize_t rpc_sysfs_xprt_state_show(struct
> kobject *kobj,
>         struct rpc_xprt *xprt = rpc_sysfs_xprt_kobj_get_xprt(kobj);
>         ssize_t ret;
>         int locked, connected, connecting, close_wait, bound,
> binding,
> -           closing, congested, cwnd_wait, write_space;
> +           closing, congested, cwnd_wait, write_space, offline;
>  
>         if (!xprt)
>                 return 0;
> @@ -136,8 +136,9 @@ static ssize_t rpc_sysfs_xprt_state_show(struct
> kobject *kobj,
>                 congested = test_bit(XPRT_CONGESTED, &xprt->state);
>                 cwnd_wait = test_bit(XPRT_CWND_WAIT, &xprt->state);
>                 write_space = test_bit(XPRT_WRITE_SPACE, &xprt-
> >state);
> +               offline = test_bit(XPRT_OFFLINE, &xprt->state);
>  
> -               ret = sprintf(buf, "state=%s %s %s %s %s %s %s %s %s
> %s\n",
> +               ret = sprintf(buf, "state=%s %s %s %s %s %s %s %s %s
> %s %s\n",
>                               locked ? "LOCKED" : "",
>                               connected ? "CONNECTED" : "",
>                               connecting ? "CONNECTING" : "",
> @@ -147,7 +148,8 @@ static ssize_t rpc_sysfs_xprt_state_show(struct
> kobject *kobj,
>                               closing ? "CLOSING" : "",
>                               congested ? "CONGESTED" : "",
>                               cwnd_wait ? "CWND_WAIT" : "",
> -                             write_space ? "WRITE_SPACE" : "");
> +                             write_space ? "WRITE_SPACE" : "",
> +                             offline ? "OFFLINE" : "");
>         }
>  
>         xprt_put(xprt);
> @@ -223,6 +225,38 @@ static ssize_t
> rpc_sysfs_xprt_dstaddr_store(struct kobject *kobj,
>         goto out;
>  }
>  
> +static ssize_t rpc_sysfs_xprt_state_change(struct kobject *kobj,
> +                                          struct kobj_attribute
> *attr,
> +                                          const char *buf, size_t
> count)
> +{
> +       struct rpc_xprt *xprt = rpc_sysfs_xprt_kobj_get_xprt(kobj);
> +       int offline = 0;
> +
> +       if (!xprt)
> +               return 0;
> +
> +       if (!strncmp(buf, "offline", 7))
> +               offline = 1;
> +       else
> +               return -EINVAL;
> +
> +       if (wait_on_bit_lock(&xprt->state, XPRT_LOCKED,
> TASK_KILLABLE)) {
> +               count = -EINTR;
> +               goto out_put;
> +       }
> +       if (offline) {
> +               if (xprt->main)
> +                       count = -EINVAL;
> +               else
> +                       set_bit(XPRT_OFFLINE, &xprt->state);
> +       }

Is there any way to put the transport back online? What say the problem
with the downed IP address gets fixed?

> +
> +       xprt_release_write(xprt, NULL);
> +out_put:
> +       xprt_put(xprt);
> +       return count;
> +}
> +
>  int rpc_sysfs_init(void)
>  {
>         rpc_sunrpc_kset = kset_create_and_add("sunrpc", NULL,
> kernel_kobj);
> @@ -293,7 +327,7 @@ static struct kobj_attribute rpc_sysfs_xprt_info
> = __ATTR(xprt_info,
>         0444, rpc_sysfs_xprt_info_show, NULL);
>  
>  static struct kobj_attribute rpc_sysfs_xprt_change_state =
> __ATTR(xprt_state,
> -       0644, rpc_sysfs_xprt_state_show, NULL);
> +       0644, rpc_sysfs_xprt_state_show,
> rpc_sysfs_xprt_state_change);
>  
>  static struct attribute *rpc_sysfs_xprt_attrs[] = {
>         &rpc_sysfs_xprt_dstaddr.attr,
> diff --git a/net/sunrpc/xprtmultipath.c b/net/sunrpc/xprtmultipath.c
> index 07e76ae1028a..39551b794b80 100644
> --- a/net/sunrpc/xprtmultipath.c
> +++ b/net/sunrpc/xprtmultipath.c
> @@ -230,7 +230,8 @@ void xprt_iter_default_rewind(struct
> rpc_xprt_iter *xpi)
>  static
>  bool xprt_is_active(const struct rpc_xprt *xprt)
>  {
> -       return kref_read(&xprt->kref) != 0;
> +       return (kref_read(&xprt->kref) != 0 &&
> +               !test_bit(XPRT_OFFLINE, &xprt->state));
>  }
>  
>  static

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