Re: [RFC PATCH 8/9] NFS: Use NFSv4.2's OFFLOAD_STATUS operation

[Chuck Lever <chuck.lever@oracle.com>]

On Tue, Oct 08, 2024 at 06:10:44PM -0400, NeilBrown wrote:
> On Wed, 09 Oct 2024, cel@kernel.org wrote:
> > From: Chuck Lever <chuck.lever@oracle.com>
> > 
> > We've found that there are cases where a transport disconnection
> > results in the loss of callback RPCs. NFS servers typically do not
> > retransmit callback operations after a disconnect.
> > 
> > This can be a problem for the Linux NFS client's current
> > implementation of asynchronous COPY, which waits indefinitely for a
> > CB_OFFLOAD callback. If a transport disconnect occurs while an async
> > COPY is running, there's a good chance the client will never get the
> > completing CB_OFFLOAD.
> > 
> > Fix this by implementing the OFFLOAD_STATUS operation so that the
> > Linux NFS client can probe the NFS server if it doesn't see a
> > CB_OFFLOAD in a reasonable amount of time.
> > 
> > This patch implements a simplistic check. As future work, the client
> > might also be able to detect whether there is no forward progress on
> > the request asynchronous COPY operation, and CANCEL it.
> > 
> > Suggested-by: Olga Kornievskaia <kolga@netapp.com>
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=218735
> > Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> > ---
> >  fs/nfs/nfs42proc.c | 56 ++++++++++++++++++++++++++++++++++++++++------
> >  1 file changed, 49 insertions(+), 7 deletions(-)
> > 
> > diff --git a/fs/nfs/nfs42proc.c b/fs/nfs/nfs42proc.c
> > index 175330843558..fc4f64750dc5 100644
> > --- a/fs/nfs/nfs42proc.c
> > +++ b/fs/nfs/nfs42proc.c
> > @@ -175,6 +175,11 @@ int nfs42_proc_deallocate(struct file *filep, loff_t offset, loff_t len)
> >  	return err;
> >  }
> >  
> > +/* Wait this long before checking progress on a COPY operation */
> > +enum {
> > +	NFS42_COPY_TIMEOUT	= 3 * HZ,
> > +};
> > +
> >  static int handle_async_copy(struct nfs42_copy_res *res,
> >  			     struct nfs_server *dst_server,
> >  			     struct nfs_server *src_server,
> > @@ -184,9 +189,10 @@ static int handle_async_copy(struct nfs42_copy_res *res,
> >  			     bool *restart)
> >  {
> >  	struct nfs4_copy_state *copy, *tmp_copy = NULL, *iter;
> > -	int status = NFS4_OK;
> >  	struct nfs_open_context *dst_ctx = nfs_file_open_context(dst);
> >  	struct nfs_open_context *src_ctx = nfs_file_open_context(src);
> > +	int status = NFS4_OK;
> > +	u64 copied;
> >  
> >  	copy = kzalloc(sizeof(struct nfs4_copy_state), GFP_KERNEL);
> >  	if (!copy)
> > @@ -224,7 +230,9 @@ static int handle_async_copy(struct nfs42_copy_res *res,
> >  		spin_unlock(&src_server->nfs_client->cl_lock);
> >  	}
> >  
> > -	status = wait_for_completion_interruptible(&copy->completion);
> > +wait:
> > +	status = wait_for_completion_interruptible_timeout(&copy->completion,
> > +							   NFS42_COPY_TIMEOUT);
> >  	spin_lock(&dst_server->nfs_client->cl_lock);
> >  	list_del_init(&copy->copies);
> >  	spin_unlock(&dst_server->nfs_client->cl_lock);
> > @@ -233,15 +241,21 @@ static int handle_async_copy(struct nfs42_copy_res *res,
> >  		list_del_init(&copy->src_copies);
> >  		spin_unlock(&src_server->nfs_client->cl_lock);
> >  	}
> > -	if (status == -ERESTARTSYS) {
> > -		goto out_cancel;
> > -	} else if (copy->flags || copy->error == NFS4ERR_PARTNER_NO_AUTH) {
> > -		status = -EAGAIN;
> > -		*restart = true;
> > +	switch (status) {
> > +	case 0:
> > +		goto timeout;
> > +	case -ERESTARTSYS:
> >  		goto out_cancel;
> > +	default:
> > +		if (copy->flags || copy->error == NFS4ERR_PARTNER_NO_AUTH) {
> > +			status = -EAGAIN;
> > +			*restart = true;
> > +			goto out_cancel;
> > +		}
> >  	}
> >  out:
> >  	res->write_res.count = copy->count;
> > +	/* Copy out the updated write verifier provided by CB_OFFLOAD. */
> >  	memcpy(&res->write_res.verifier, &copy->verf, sizeof(copy->verf));
> >  	status = -copy->error;
> >  
> > @@ -253,6 +267,34 @@ static int handle_async_copy(struct nfs42_copy_res *res,
> >  	if (!nfs42_files_from_same_server(src, dst))
> >  		nfs42_do_offload_cancel_async(src, src_stateid);
> >  	goto out_free;
> > +timeout:
> > +	status = nfs42_proc_offload_status(src, &copy->stateid, &copied);
> > +	switch (status) {
> > +	case 0:
> > +	case -EREMOTEIO:
> > +		/* The server recognized the copy stateid, so it hasn't
> > +		 * rebooted. Don't overwrite the verifier returned in the
> > +		 * COPY result. */
> > +		res->write_res.count = copied;
> > +		goto out_free;
> > +	case -EINPROGRESS:
> > +		goto wait;
> > +	case -EBADF:
> > +		/* Server did not recognize the copy stateid. It has
> > +		 * probably restarted and lost the plot. State recovery
> > +		 * might redrive the COPY from the beginning, in this
> > +		 * case? */
> > +		res->write_res.count = 0;
> > +		status = -EREMOTEIO;
> > +		break;
> > +	case -EOPNOTSUPP:
> > +		/* RFC 7862 REQUIREs server to support OFFLOAD_STATUS when
> > +		 * it has signed up for an async COPY, so server is not
> > +		 * spec-compliant. */
> > +		res->write_res.count = 0;
> > +		status = -EREMOTEIO;
> 
> Should -ERESTARTSYS be handled here?

The "default" is to "goto out;" handle_async_copy() will return
-ERESTARTSYS in that case. What more should be done?


> NeilBrown
> 
> 
> > +	}
> > +	goto out;
> >  }
> >  
> >  static int process_copy_commit(struct file *dst, loff_t pos_dst,
> > -- 
> > 2.46.2
> > 
> > 
> > 
> 

-- 
Chuck Lever