PATCH [v3 0/2] NFSD: use CB_GETATTR to handle GETATTR conflict with write delegation

PATCH [v3 0/2] NFSD: use CB_GETATTR to handle GETATTR conflict with write delegation

[Dai Ngo]

Currently GETATTR conflict with a write delegation is handled by
recalling the delegation before replying to the GETATTR.

This patch series add supports for CB_GETATTR callback to get the latest
change_info and size information of the file from the client that holds
the delegation to reply to the GETATTR from the second client.

NOTE: this patch series is mostly the same as the previous patches which
were backed out when un unrelated problem of NFSD server hang on reboot
was reported.

The only difference is the wait_on_bit() in nfsd4_deleg_getattr_conflict was
replaced with wait_on_bit_timeout() with 30ms timeout to avoid a potential
DOS attack by exhausting NFSD kernel threads with GETATTR conflicts.

v2:
  . update comments in nfsd4_deleg_getattr_conflict

v3:
  . rebase with nfsd-next

 fs/nfsd/nfs4callback.c |  97 ++++++++++++++++++++++++++++++++++++-
 fs/nfsd/nfs4state.c    | 115 ++++++++++++++++++++++++++++++++++++++++----
 fs/nfsd/nfs4xdr.c      |  10 +++-
 fs/nfsd/nfsd.h         |   1 +
 fs/nfsd/state.h        |  24 ++++++++-
 fs/nfsd/xdr4cb.h       |  18 +++++++
 6 files changed, 251 insertions(+), 14 deletions(-)

[PATCH v3 1/2] NFSD: add supports for CB_GETATTR callback

[Dai Ngo]

Includes:
   . CB_GETATTR proc for nfs4_cb_procedures[]
   . XDR encoding and decoding function for CB_GETATTR request/reply
   . add nfs4_cb_fattr to nfs4_delegation for sending CB_GETATTR
     and store file attributes from client's reply.

Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
---
 fs/nfsd/nfs4callback.c | 97 +++++++++++++++++++++++++++++++++++++++++-
 fs/nfsd/state.h        | 14 ++++++
 fs/nfsd/xdr4cb.h       | 18 ++++++++
 3 files changed, 128 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index 32dd2fbb1f30..e440f72b9d4e 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -85,7 +85,21 @@ static void encode_uint32(struct xdr_stream *xdr, u32 n)
 static void encode_bitmap4(struct xdr_stream *xdr, const __u32 *bitmap,
 			   size_t len)
 {
-	WARN_ON_ONCE(xdr_stream_encode_uint32_array(xdr, bitmap, len) < 0);
+	xdr_stream_encode_uint32_array(xdr, bitmap, len);
+}
+
+static int decode_cb_fattr4(struct xdr_stream *xdr, uint32_t *bitmap,
+				struct nfs4_cb_fattr *fattr)
+{
+	fattr->ncf_cb_change = 0;
+	fattr->ncf_cb_fsize = 0;
+	if (bitmap[0] & FATTR4_WORD0_CHANGE)
+		if (xdr_stream_decode_u64(xdr, &fattr->ncf_cb_change) < 0)
+			return -NFSERR_BAD_XDR;
+	if (bitmap[0] & FATTR4_WORD0_SIZE)
+		if (xdr_stream_decode_u64(xdr, &fattr->ncf_cb_fsize) < 0)
+			return -NFSERR_BAD_XDR;
+	return 0;
 }
 
 static void encode_nfs_cb_opnum4(struct xdr_stream *xdr, enum nfs_cb_opnum4 op)
@@ -333,6 +347,30 @@ encode_cb_recallany4args(struct xdr_stream *xdr,
 	hdr->nops++;
 }
 
+/*
+ * CB_GETATTR4args
+ *	struct CB_GETATTR4args {
+ *	   nfs_fh4 fh;
+ *	   bitmap4 attr_request;
+ *	};
+ *
+ * The size and change attributes are the only one
+ * guaranteed to be serviced by the client.
+ */
+static void
+encode_cb_getattr4args(struct xdr_stream *xdr, struct nfs4_cb_compound_hdr *hdr,
+			struct nfs4_cb_fattr *fattr)
+{
+	struct nfs4_delegation *dp =
+		container_of(fattr, struct nfs4_delegation, dl_cb_fattr);
+	struct knfsd_fh *fh = &dp->dl_stid.sc_file->fi_fhandle;
+
+	encode_nfs_cb_opnum4(xdr, OP_CB_GETATTR);
+	encode_nfs_fh4(xdr, fh);
+	encode_bitmap4(xdr, fattr->ncf_cb_bmap, ARRAY_SIZE(fattr->ncf_cb_bmap));
+	hdr->nops++;
+}
+
 /*
  * CB_SEQUENCE4args
  *
@@ -468,6 +506,26 @@ static void nfs4_xdr_enc_cb_null(struct rpc_rqst *req, struct xdr_stream *xdr,
 	xdr_reserve_space(xdr, 0);
 }
 
+/*
+ * 20.1.  Operation 3: CB_GETATTR - Get Attributes
+ */
+static void nfs4_xdr_enc_cb_getattr(struct rpc_rqst *req,
+		struct xdr_stream *xdr, const void *data)
+{
+	const struct nfsd4_callback *cb = data;
+	struct nfs4_cb_fattr *ncf =
+		container_of(cb, struct nfs4_cb_fattr, ncf_getattr);
+	struct nfs4_cb_compound_hdr hdr = {
+		.ident = cb->cb_clp->cl_cb_ident,
+		.minorversion = cb->cb_clp->cl_minorversion,
+	};
+
+	encode_cb_compound4args(xdr, &hdr);
+	encode_cb_sequence4args(xdr, cb, &hdr);
+	encode_cb_getattr4args(xdr, &hdr, ncf);
+	encode_cb_nops(&hdr);
+}
+
 /*
  * 20.2. Operation 4: CB_RECALL - Recall a Delegation
  */
@@ -523,6 +581,42 @@ static int nfs4_xdr_dec_cb_null(struct rpc_rqst *req, struct xdr_stream *xdr,
 	return 0;
 }
 
+/*
+ * 20.1.  Operation 3: CB_GETATTR - Get Attributes
+ */
+static int nfs4_xdr_dec_cb_getattr(struct rpc_rqst *rqstp,
+				  struct xdr_stream *xdr,
+				  void *data)
+{
+	struct nfsd4_callback *cb = data;
+	struct nfs4_cb_compound_hdr hdr;
+	int status;
+	u32 bitmap[3] = {0};
+	u32 attrlen;
+	struct nfs4_cb_fattr *ncf =
+		container_of(cb, struct nfs4_cb_fattr, ncf_getattr);
+
+	status = decode_cb_compound4res(xdr, &hdr);
+	if (unlikely(status))
+		return status;
+
+	status = decode_cb_sequence4res(xdr, cb);
+	if (unlikely(status || cb->cb_seq_status))
+		return status;
+
+	status = decode_cb_op_status(xdr, OP_CB_GETATTR, &cb->cb_status);
+	if (status)
+		return status;
+	if (xdr_stream_decode_uint32_array(xdr, bitmap, 3) < 0)
+		return -NFSERR_BAD_XDR;
+	if (xdr_stream_decode_u32(xdr, &attrlen) < 0)
+		return -NFSERR_BAD_XDR;
+	if (attrlen > (sizeof(ncf->ncf_cb_change) + sizeof(ncf->ncf_cb_fsize)))
+		return -NFSERR_BAD_XDR;
+	status = decode_cb_fattr4(xdr, bitmap, ncf);
+	return status;
+}
+
 /*
  * 20.2. Operation 4: CB_RECALL - Recall a Delegation
  */
@@ -831,6 +925,7 @@ static const struct rpc_procinfo nfs4_cb_procedures[] = {
 	PROC(CB_NOTIFY_LOCK,	COMPOUND,	cb_notify_lock,	cb_notify_lock),
 	PROC(CB_OFFLOAD,	COMPOUND,	cb_offload,	cb_offload),
 	PROC(CB_RECALL_ANY,	COMPOUND,	cb_recall_any,	cb_recall_any),
+	PROC(CB_GETATTR,	COMPOUND,	cb_getattr,	cb_getattr),
 };
 
 static unsigned int nfs4_cb_counts[ARRAY_SIZE(nfs4_cb_procedures)];
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index 0c8ec578ba7e..3bf418ee6c97 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -134,6 +134,16 @@ struct nfs4_cpntf_state {
 	time64_t		cpntf_time;	/* last time stateid used */
 };
 
+struct nfs4_cb_fattr {
+	struct nfsd4_callback ncf_getattr;
+	u32 ncf_cb_status;
+	u32 ncf_cb_bmap[1];
+
+	/* from CB_GETATTR reply */
+	u64 ncf_cb_change;
+	u64 ncf_cb_fsize;
+};
+
 /*
  * Represents a delegation stateid. The nfs4_client holds references to these
  * and they are put when it is being destroyed or when the delegation is
@@ -167,6 +177,9 @@ struct nfs4_delegation {
 	int			dl_retries;
 	struct nfsd4_callback	dl_recall;
 	bool			dl_recalled;
+
+	/* for CB_GETATTR */
+	struct nfs4_cb_fattr    dl_cb_fattr;
 };
 
 #define cb_to_delegation(cb) \
@@ -659,6 +672,7 @@ enum nfsd4_cb_op {
 	NFSPROC4_CLNT_CB_SEQUENCE,
 	NFSPROC4_CLNT_CB_NOTIFY_LOCK,
 	NFSPROC4_CLNT_CB_RECALL_ANY,
+	NFSPROC4_CLNT_CB_GETATTR,
 };
 
 /* Returns true iff a is later than b: */
diff --git a/fs/nfsd/xdr4cb.h b/fs/nfsd/xdr4cb.h
index 0d39af1b00a0..e8b00309c449 100644
--- a/fs/nfsd/xdr4cb.h
+++ b/fs/nfsd/xdr4cb.h
@@ -54,3 +54,21 @@
 #define NFS4_dec_cb_recall_any_sz	(cb_compound_dec_hdr_sz  +      \
 					cb_sequence_dec_sz +            \
 					op_dec_sz)
+
+/*
+ * 1: CB_GETATTR opcode (32-bit)
+ * N: file_handle
+ * 1: number of entry in attribute array (32-bit)
+ * 1: entry 0 in attribute array (32-bit)
+ */
+#define NFS4_enc_cb_getattr_sz		(cb_compound_enc_hdr_sz +       \
+					cb_sequence_enc_sz +            \
+					1 + enc_nfs4_fh_sz + 1 + 1)
+/*
+ * 4: fattr_bitmap_maxsz
+ * 1: attribute array len
+ * 2: change attr (64-bit)
+ * 2: size (64-bit)
+ */
+#define NFS4_dec_cb_getattr_sz		(cb_compound_dec_hdr_sz  +      \
+			cb_sequence_dec_sz + 4 + 1 + 2 + 2 + op_dec_sz)
-- 
2.39.3

[PATCH v3 2/2] NFSD: handle GETATTR conflict with write delegation

[Dai Ngo]

If the GETATTR request on a file that has write delegation in effect
and the request attributes include the change info and size attribute
then the request is handled as below:

Server sends CB_GETATTR to client to get the latest change info and file
size. If these values are the same as the server's cached values then
the GETATTR proceeds as normal.

If either the change info or file size is different from the server's
cached values, or the file was already marked as modified, then:

    . update time_modify and time_metadata into file's metadata
      with current time

    . encode GETATTR as normal except the file size is encoded with
      the value returned from CB_GETATTR

    . mark the file as modified

If the CB_GETATTR fails for any reasons, the delegation is recalled
and NFS4ERR_DELAY is returned for the GETATTR.

Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
---
 fs/nfsd/nfs4state.c | 115 ++++++++++++++++++++++++++++++++++++++++----
 fs/nfsd/nfs4xdr.c   |  10 +++-
 fs/nfsd/nfsd.h      |   1 +
 fs/nfsd/state.h     |  10 +++-
 4 files changed, 123 insertions(+), 13 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index d9260e77ef2d..948148182cc5 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -127,6 +127,7 @@ static void free_session(struct nfsd4_session *);
 
 static const struct nfsd4_callback_ops nfsd4_cb_recall_ops;
 static const struct nfsd4_callback_ops nfsd4_cb_notify_lock_ops;
+static const struct nfsd4_callback_ops nfsd4_cb_getattr_ops;
 
 static struct workqueue_struct *laundry_wq;
 
@@ -1189,6 +1190,10 @@ alloc_init_deleg(struct nfs4_client *clp, struct nfs4_file *fp,
 	dp->dl_recalled = false;
 	nfsd4_init_cb(&dp->dl_recall, dp->dl_stid.sc_client,
 		      &nfsd4_cb_recall_ops, NFSPROC4_CLNT_CB_RECALL);
+	nfsd4_init_cb(&dp->dl_cb_fattr.ncf_getattr, dp->dl_stid.sc_client,
+			&nfsd4_cb_getattr_ops, NFSPROC4_CLNT_CB_GETATTR);
+	dp->dl_cb_fattr.ncf_file_modified = false;
+	dp->dl_cb_fattr.ncf_cb_bmap[0] = FATTR4_WORD0_CHANGE | FATTR4_WORD0_SIZE;
 	get_nfs4_file(fp);
 	dp->dl_stid.sc_file = fp;
 	return dp;
@@ -3044,11 +3049,59 @@ nfsd4_cb_recall_any_release(struct nfsd4_callback *cb)
 	spin_unlock(&nn->client_lock);
 }
 
+static int
+nfsd4_cb_getattr_done(struct nfsd4_callback *cb, struct rpc_task *task)
+{
+	struct nfs4_cb_fattr *ncf =
+			container_of(cb, struct nfs4_cb_fattr, ncf_getattr);
+
+	ncf->ncf_cb_status = task->tk_status;
+	switch (task->tk_status) {
+	case -NFS4ERR_DELAY:
+		rpc_delay(task, 2 * HZ);
+		return 0;
+	default:
+		return 1;
+	}
+}
+
+static void
+nfsd4_cb_getattr_release(struct nfsd4_callback *cb)
+{
+	struct nfs4_cb_fattr *ncf =
+			container_of(cb, struct nfs4_cb_fattr, ncf_getattr);
+	struct nfs4_delegation *dp =
+			container_of(ncf, struct nfs4_delegation, dl_cb_fattr);
+
+	nfs4_put_stid(&dp->dl_stid);
+	clear_bit(CB_GETATTR_BUSY, &ncf->ncf_cb_flags);
+	wake_up_bit(&ncf->ncf_cb_flags, CB_GETATTR_BUSY);
+}
+
 static const struct nfsd4_callback_ops nfsd4_cb_recall_any_ops = {
 	.done		= nfsd4_cb_recall_any_done,
 	.release	= nfsd4_cb_recall_any_release,
 };
 
+static const struct nfsd4_callback_ops nfsd4_cb_getattr_ops = {
+	.done		= nfsd4_cb_getattr_done,
+	.release	= nfsd4_cb_getattr_release,
+};
+
+static void nfs4_cb_getattr(struct nfs4_cb_fattr *ncf)
+{
+	struct nfs4_delegation *dp =
+			container_of(ncf, struct nfs4_delegation, dl_cb_fattr);
+
+	if (test_and_set_bit(CB_GETATTR_BUSY, &ncf->ncf_cb_flags))
+		return;
+	/* set to proper status when nfsd4_cb_getattr_done runs */
+	ncf->ncf_cb_status = NFS4ERR_IO;
+
+	refcount_inc(&dp->dl_stid.sc_count);
+	nfsd4_run_cb(&ncf->ncf_getattr);
+}
+
 static struct nfs4_client *create_client(struct xdr_netobj name,
 		struct svc_rqst *rqstp, nfs4_verifier *verf)
 {
@@ -5854,6 +5907,8 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
 	struct svc_fh *parent = NULL;
 	int cb_up;
 	int status = 0;
+	struct kstat stat;
+	struct path path;
 
 	cb_up = nfsd4_cb_channel_good(oo->oo_owner.so_client);
 	open->op_recall = false;
@@ -5891,6 +5946,18 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
 	if (open->op_share_access & NFS4_SHARE_ACCESS_WRITE) {
 		open->op_delegate_type = NFS4_OPEN_DELEGATE_WRITE;
 		trace_nfsd_deleg_write(&dp->dl_stid.sc_stateid);
+		path.mnt = currentfh->fh_export->ex_path.mnt;
+		path.dentry = currentfh->fh_dentry;
+		if (vfs_getattr(&path, &stat,
+				(STATX_SIZE | STATX_CTIME | STATX_CHANGE_COOKIE),
+				AT_STATX_SYNC_AS_STAT)) {
+			nfs4_put_stid(&dp->dl_stid);
+			destroy_delegation(dp);
+			goto out_no_deleg;
+		}
+		dp->dl_cb_fattr.ncf_cur_fsize = stat.size;
+		dp->dl_cb_fattr.ncf_initial_cinfo =
+			nfsd4_change_attribute(&stat, d_inode(currentfh->fh_dentry));
 	} else {
 		open->op_delegate_type = NFS4_OPEN_DELEGATE_READ;
 		trace_nfsd_deleg_read(&dp->dl_stid.sc_stateid);
@@ -8720,6 +8787,8 @@ nfsd4_get_writestateid(struct nfsd4_compound_state *cstate,
  * nfsd4_deleg_getattr_conflict - Recall if GETATTR causes conflict
  * @rqstp: RPC transaction context
  * @inode: file to be checked for a conflict
+ * @modified: return true if file was modified
+ * @size: new size of file if modified is true
  *
  * This function is called when there is a conflict between a write
  * delegation and a change/size GETATTR from another client. The server
@@ -8728,22 +8797,22 @@ nfsd4_get_writestateid(struct nfsd4_compound_state *cstate,
  * delegation before replying to the GETATTR. See RFC 8881 section
  * 18.7.4.
  *
- * The current implementation does not support CB_GETATTR yet. However
- * this can avoid recalling the delegation could be added in follow up
- * work.
- *
  * Returns 0 if there is no conflict; otherwise an nfs_stat
  * code is returned.
  */
 __be32
-nfsd4_deleg_getattr_conflict(struct svc_rqst *rqstp, struct inode *inode)
+nfsd4_deleg_getattr_conflict(struct svc_rqst *rqstp, struct inode *inode,
+				bool *modified, u64 *size)
 {
 	__be32 status;
 	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
 	struct file_lock_context *ctx;
 	struct file_lock *fl;
 	struct nfs4_delegation *dp;
+	struct iattr attrs;
+	struct nfs4_cb_fattr *ncf;
 
+	*modified = false;
 	ctx = locks_inode_context(inode);
 	if (!ctx)
 		return 0;
@@ -8768,12 +8837,38 @@ nfsd4_deleg_getattr_conflict(struct svc_rqst *rqstp, struct inode *inode)
 				return 0;
 			}
 break_lease:
-			spin_unlock(&ctx->flc_lock);
 			nfsd_stats_wdeleg_getattr_inc(nn);
-			status = nfserrno(nfsd_open_break_lease(inode, NFSD_MAY_READ));
-			if (status != nfserr_jukebox ||
-					!nfsd_wait_for_delegreturn(rqstp, inode))
-				return status;
+			dp = fl->fl_owner;
+			ncf = &dp->dl_cb_fattr;
+			nfs4_cb_getattr(&dp->dl_cb_fattr);
+			spin_unlock(&ctx->flc_lock);
+			wait_on_bit_timeout(&ncf->ncf_cb_flags, CB_GETATTR_BUSY,
+					TASK_INTERRUPTIBLE, NFSD_CB_GETATTR_TIMEOUT);
+			if (ncf->ncf_cb_status) {
+				/* Recall delegation only if client didn't respond */
+				status = nfserrno(nfsd_open_break_lease(inode, NFSD_MAY_READ));
+				if (status != nfserr_jukebox ||
+						!nfsd_wait_for_delegreturn(rqstp, inode))
+					return status;
+			}
+			if (!ncf->ncf_file_modified &&
+					(ncf->ncf_initial_cinfo != ncf->ncf_cb_change ||
+					ncf->ncf_cur_fsize != ncf->ncf_cb_fsize))
+				ncf->ncf_file_modified = true;
+			if (ncf->ncf_file_modified) {
+				/*
+				 * Per section 10.4.3 of RFC 8881, the server would
+				 * not update the file's metadata with the client's
+				 * modified size
+				 */
+				attrs.ia_mtime = attrs.ia_ctime = current_time(inode);
+				attrs.ia_valid = ATTR_MTIME | ATTR_CTIME;
+				setattr_copy(&nop_mnt_idmap, inode, &attrs);
+				mark_inode_dirty(inode);
+				ncf->ncf_cur_fsize = ncf->ncf_cb_fsize;
+				*size = ncf->ncf_cur_fsize;
+				*modified = true;
+			}
 			return 0;
 		}
 		break;
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index e3f761cd5ee7..9e8f230fc96e 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -3507,6 +3507,8 @@ nfsd4_encode_fattr4(struct svc_rqst *rqstp, struct xdr_stream *xdr,
 		unsigned long	mask[2];
 	} u;
 	unsigned long bit;
+	bool file_modified = false;
+	u64 size = 0;
 
 	WARN_ON_ONCE(bmval[1] & NFSD_WRITEONLY_ATTRS_WORD1);
 	WARN_ON_ONCE(!nfsd_attrs_supported(minorversion, bmval));
@@ -3533,7 +3535,8 @@ nfsd4_encode_fattr4(struct svc_rqst *rqstp, struct xdr_stream *xdr,
 	}
 	args.size = 0;
 	if (u.attrmask[0] & (FATTR4_WORD0_CHANGE | FATTR4_WORD0_SIZE)) {
-		status = nfsd4_deleg_getattr_conflict(rqstp, d_inode(dentry));
+		status = nfsd4_deleg_getattr_conflict(rqstp, d_inode(dentry),
+					&file_modified, &size);
 		if (status)
 			goto out;
 	}
@@ -3543,7 +3546,10 @@ nfsd4_encode_fattr4(struct svc_rqst *rqstp, struct xdr_stream *xdr,
 			  AT_STATX_SYNC_AS_STAT);
 	if (err)
 		goto out_nfserr;
-	args.size = args.stat.size;
+	if (file_modified)
+		args.size = size;
+	else
+		args.size = args.stat.size;
 
 	if (!(args.stat.result_mask & STATX_BTIME))
 		/* underlying FS does not offer btime so we can't share it */
diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
index 8daf22d766c6..16c5a05f340e 100644
--- a/fs/nfsd/nfsd.h
+++ b/fs/nfsd/nfsd.h
@@ -367,6 +367,7 @@ void		nfsd_lockd_shutdown(void);
 #define	NFSD_CLIENT_MAX_TRIM_PER_RUN	128
 #define	NFS4_CLIENTS_PER_GB		1024
 #define NFSD_DELEGRETURN_TIMEOUT	(HZ / 34)	/* 30ms */
+#define	NFSD_CB_GETATTR_TIMEOUT		NFSD_DELEGRETURN_TIMEOUT
 
 /*
  * The following attributes are currently not supported by the NFSv4 server:
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index 3bf418ee6c97..01c6f3445646 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -142,8 +142,16 @@ struct nfs4_cb_fattr {
 	/* from CB_GETATTR reply */
 	u64 ncf_cb_change;
 	u64 ncf_cb_fsize;
+
+	unsigned long ncf_cb_flags;
+	bool ncf_file_modified;
+	u64 ncf_initial_cinfo;
+	u64 ncf_cur_fsize;
 };
 
+/* bits for ncf_cb_flags */
+#define	CB_GETATTR_BUSY		0
+
 /*
  * Represents a delegation stateid. The nfs4_client holds references to these
  * and they are put when it is being destroyed or when the delegation is
@@ -773,5 +781,5 @@ static inline bool try_to_expire_client(struct nfs4_client *clp)
 }
 
 extern __be32 nfsd4_deleg_getattr_conflict(struct svc_rqst *rqstp,
-				struct inode *inode);
+		struct inode *inode, bool *file_modified, u64 *size);
 #endif   /* NFSD4_STATE_H */
-- 
2.39.3

Re: PATCH [v3 0/2] NFSD: use CB_GETATTR to handle GETATTR conflict with write delegation

[Chuck Lever]

On Thu, Feb 15, 2024 at 02:05:20PM -0800, Dai Ngo wrote:
> Currently GETATTR conflict with a write delegation is handled by
> recalling the delegation before replying to the GETATTR.
> 
> This patch series add supports for CB_GETATTR callback to get the latest
> change_info and size information of the file from the client that holds
> the delegation to reply to the GETATTR from the second client.
> 
> NOTE: this patch series is mostly the same as the previous patches which
> were backed out when un unrelated problem of NFSD server hang on reboot
> was reported.
> 
> The only difference is the wait_on_bit() in nfsd4_deleg_getattr_conflict was
> replaced with wait_on_bit_timeout() with 30ms timeout to avoid a potential
> DOS attack by exhausting NFSD kernel threads with GETATTR conflicts.
> 
> v2:
>   . update comments in nfsd4_deleg_getattr_conflict
> 
> v3:
>   . rebase with nfsd-next
> 
>  fs/nfsd/nfs4callback.c |  97 ++++++++++++++++++++++++++++++++++++-
>  fs/nfsd/nfs4state.c    | 115 ++++++++++++++++++++++++++++++++++++++++----
>  fs/nfsd/nfs4xdr.c      |  10 +++-
>  fs/nfsd/nfsd.h         |   1 +
>  fs/nfsd/state.h        |  24 ++++++++-
>  fs/nfsd/xdr4cb.h       |  18 +++++++
>  6 files changed, 251 insertions(+), 14 deletions(-)
> 

Applied to nfsd-next. Thanks for your efforts!

-- 
Chuck Lever

Re: PATCH [v3 0/2] NFSD: use CB_GETATTR to handle GETATTR conflict with write delegation

[Dan Shelton]

On Thu, 15 Feb 2024 at 23:11, Dai Ngo <dai.ngo@oracle.com> wrote:
>
> Currently GETATTR conflict with a write delegation is handled by
> recalling the delegation before replying to the GETATTR.
>
> This patch series add supports for CB_GETATTR callback to get the latest
> change_info and size information of the file from the client that holds
> the delegation to reply to the GETATTR from the second client.
>
> NOTE: this patch series is mostly the same as the previous patches which
> were backed out when un unrelated problem of NFSD server hang on reboot
> was reported.
>
> The only difference is the wait_on_bit() in nfsd4_deleg_getattr_conflict was
> replaced with wait_on_bit_timeout() with 30ms timeout to avoid a potential
> DOS attack by exhausting NFSD kernel threads with GETATTR conflicts.

I have a concern about this static and very tiny timeout.
What will happen if the ICMPv6 latency is well over 30ms, like 660ms
(average 250mbit/s satellite latency)?

Would that not ruin delegations?

Dan
-- 
Dan Shelton - Cluster Specialist Win/Lin/Bsd

Re: PATCH [v3 0/2] NFSD: use CB_GETATTR to handle GETATTR conflict with write delegation

[Trond Myklebust]

On Sat, 2024-02-17 at 00:34 +0100, Dan Shelton wrote:
> On Thu, 15 Feb 2024 at 23:11, Dai Ngo <dai.ngo@oracle.com> wrote:
> > 
> > Currently GETATTR conflict with a write delegation is handled by
> > recalling the delegation before replying to the GETATTR.
> > 
> > This patch series add supports for CB_GETATTR callback to get the
> > latest
> > change_info and size information of the file from the client that
> > holds
> > the delegation to reply to the GETATTR from the second client.
> > 
> > NOTE: this patch series is mostly the same as the previous patches
> > which
> > were backed out when un unrelated problem of NFSD server hang on
> > reboot
> > was reported.
> > 
> > The only difference is the wait_on_bit() in
> > nfsd4_deleg_getattr_conflict was
> > replaced with wait_on_bit_timeout() with 30ms timeout to avoid a
> > potential
> > DOS attack by exhausting NFSD kernel threads with GETATTR
> > conflicts.
> 
> I have a concern about this static and very tiny timeout.
> What will happen if the ICMPv6 latency is well over 30ms, like 660ms
> (average 250mbit/s satellite latency)?
> 
> Would that not ruin delegations?

That's a very valid point, not least because clients do not optimise
for back channel RPC calls, and because the consequences of a timeout
would be either to recall the delegation or to fence the client. The
former just makes a bad back channel situation worse. The latter just
interrupts I/O for no good reason
.

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

Re: PATCH [v3 0/2] NFSD: use CB_GETATTR to handle GETATTR conflict with write delegation

[Chuck Lever]

On Sat, Feb 17, 2024 at 12:34:45AM +0100, Dan Shelton wrote:
> On Thu, 15 Feb 2024 at 23:11, Dai Ngo <dai.ngo@oracle.com> wrote:
> >
> > Currently GETATTR conflict with a write delegation is handled by
> > recalling the delegation before replying to the GETATTR.
> >
> > This patch series add supports for CB_GETATTR callback to get the latest
> > change_info and size information of the file from the client that holds
> > the delegation to reply to the GETATTR from the second client.
> >
> > NOTE: this patch series is mostly the same as the previous patches which
> > were backed out when un unrelated problem of NFSD server hang on reboot
> > was reported.
> >
> > The only difference is the wait_on_bit() in nfsd4_deleg_getattr_conflict was
> > replaced with wait_on_bit_timeout() with 30ms timeout to avoid a potential
> > DOS attack by exhausting NFSD kernel threads with GETATTR conflicts.
> 
> I have a concern about this static and very tiny timeout.
> What will happen if the ICMPv6 latency is well over 30ms, like 660ms
> (average 250mbit/s satellite latency)?

CB_GETATTR is an optimization for write delegation. Without
CB_GETATTR, or if the client does not respond within 30ms, the
server recalls the delegation. We expect no impact on clients
that connect on a high bandwidth-latency product link.

To lengthen that timeout would require the implementation of a
mechanism for NFSD to defer requests without tying up an NFSD
thread. So for the moment, the proposed CB_GETATTR implementation
will help fast local clients but should not negatively impact
remote clients, and we cannot in good faith provide a tunable
to extend that timeout beyond a few dozen milliseconds.


> Would that not ruin delegations?

As stated above, it should not impact write delegation, and Dai can
correct me if I'm wrong, but I believe CB_GETATTR is not used if the
server has offered a read delegation. NFSD implemented only read
delegation until very recently.

IIRC, there is instrumentation in v6.6 or v6.7's NFSD to measure
how often a CB_GETATTR might have been beneficial. I can provide
more detail when I'm in front of my desktop computer.


-- 
Chuck Lever

Re: PATCH [v3 0/2] NFSD: use CB_GETATTR to handle GETATTR conflict with write delegation

[dai.ngo]

On 2/16/24 6:17 PM, Chuck Lever wrote:
> On Sat, Feb 17, 2024 at 12:34:45AM +0100, Dan Shelton wrote:
>> On Thu, 15 Feb 2024 at 23:11, Dai Ngo <dai.ngo@oracle.com> wrote:
>>> Currently GETATTR conflict with a write delegation is handled by
>>> recalling the delegation before replying to the GETATTR.
>>>
>>> This patch series add supports for CB_GETATTR callback to get the latest
>>> change_info and size information of the file from the client that holds
>>> the delegation to reply to the GETATTR from the second client.
>>>
>>> NOTE: this patch series is mostly the same as the previous patches which
>>> were backed out when un unrelated problem of NFSD server hang on reboot
>>> was reported.
>>>
>>> The only difference is the wait_on_bit() in nfsd4_deleg_getattr_conflict was
>>> replaced with wait_on_bit_timeout() with 30ms timeout to avoid a potential
>>> DOS attack by exhausting NFSD kernel threads with GETATTR conflicts.
>> I have a concern about this static and very tiny timeout.
>> What will happen if the ICMPv6 latency is well over 30ms, like 660ms
>> (average 250mbit/s satellite latency)?
> CB_GETATTR is an optimization for write delegation. Without
> CB_GETATTR, or if the client does not respond within 30ms, the
> server recalls the delegation. We expect no impact on clients
> that connect on a high bandwidth-latency product link.
>
> To lengthen that timeout would require the implementation of a
> mechanism for NFSD to defer requests without tying up an NFSD
> thread. So for the moment, the proposed CB_GETATTR implementation
> will help fast local clients but should not negatively impact
> remote clients, and we cannot in good faith provide a tunable
> to extend that timeout beyond a few dozen milliseconds.
>
>
>> Would that not ruin delegations?
> As stated above, it should not impact write delegation, and Dai can
> correct me if I'm wrong, but I believe CB_GETATTR is not used if the
> server has offered a read delegation.

Yes, CB_GETATTR is only used for write delegation.

>   NFSD implemented only read
> delegation until very recently.
>
> IIRC, there is instrumentation in v6.6 or v6.7's NFSD to measure
> how often a CB_GETATTR might have been beneficial. I can provide
> more detail when I'm in front of my desktop computer.

# cat  /proc/net/rpc/nfsd |grep wdele

-Dai

>
>