[RFC PATCH 2/9] NFSD: Free async copy information in nfsd4_cb_offload_release()

[cel@xxxxxxxxxx]

From: Chuck Lever <chuck.lever@xxxxxxxxxx>

RFC 7862 Section 4.8 states:

> A copy offload stateid will be valid until either (A) the client
> or server restarts or (B) the client returns the resource by
> issuing an OFFLOAD_CANCEL operation or the client replies to a
> CB_OFFLOAD operation.

Currently, NFSD purges the metadata for an async COPY operation as
soon as the CB_OFFLOAD callback has been sent. It does not wait for
even the client's CB_OFFLOAD response, as the paragraph above
suggests that it should.

This makes the OFFLOAD_STATUS operation ineffective in the window
between the completion of the COPY and the server's receipt of the
CB_OFFLOAD response. This is important if, for example, the client
responds with NFS4ERR_DELAY, or the transport is lost before the
server receives the response. A client might use OFFLOAD_STATUS to
query the server about the missing CB_OFFLOAD, but NFSD will respond
to OFFLOAD_STATUS as if it had never heard of the presented copy
stateid.

This patch starts to address this issue by extending the lifetime of
struct nfsd4_copy at least until the server has seen the CB_OFFLOAD
response, or its CB_OFFLOAD operation has timed out.

Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
 fs/nfsd/nfs4proc.c | 18 +++++++++++-------
 fs/nfsd/xdr4.h     |  3 +++
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index b5a6bf4f459f..a3c564a9596c 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -57,6 +57,8 @@ module_param(inter_copy_offload_enable, bool, 0644);
 MODULE_PARM_DESC(inter_copy_offload_enable,
 		 "Enable inter server to server copy offload. Default: false");
 
+static void cleanup_async_copy(struct nfsd4_copy *copy);
+
 #ifdef CONFIG_NFSD_V4_2_INTER_SSC
 static int nfsd4_ssc_umount_timeout = 900000;		/* default to 15 mins */
 module_param(nfsd4_ssc_umount_timeout, int, 0644);
@@ -1598,8 +1600,10 @@ static void nfsd4_cb_offload_release(struct nfsd4_callback *cb)
 {
 	struct nfsd4_cb_offload *cbo =
 		container_of(cb, struct nfsd4_cb_offload, co_cb);
+	struct nfsd4_copy *copy =
+		container_of(cbo, struct nfsd4_copy, cp_cb_offload);
 
-	kfree(cbo);
+	cleanup_async_copy(copy);
 }
 
 static int nfsd4_cb_offload_done(struct nfsd4_callback *cb,
@@ -1730,13 +1734,10 @@ static void cleanup_async_copy(struct nfsd4_copy *copy)
 	nfs4_put_copy(copy);
 }
 
+/* Kick off a CB_OFFLOAD callback, but don't wait for the response */
 static void nfsd4_send_cb_offload(struct nfsd4_copy *copy)
 {
-	struct nfsd4_cb_offload *cbo;
-
-	cbo = kzalloc(sizeof(*cbo), GFP_KERNEL);
-	if (!cbo)
-		return;
+	struct nfsd4_cb_offload *cbo = &copy->cp_cb_offload;
 
 	memcpy(&cbo->co_res, &copy->cp_res, sizeof(copy->cp_res));
 	memcpy(&cbo->co_fh, &copy->fh, sizeof(copy->fh));
@@ -1786,10 +1787,13 @@ static int nfsd4_do_async_copy(void *data)
 	}
 
 do_callback:
+	/* The kthread exits forthwith. Ensure that a subsequent
+	 * OFFLOAD_CANCEL won't try to kill it again. */
+	set_bit(NFSD4_COPY_F_STOPPED, &copy->cp_flags);
+
 	set_bit(NFSD4_COPY_F_COMPLETED, &copy->cp_flags);
 	trace_nfsd_copy_async_done(copy);
 	nfsd4_send_cb_offload(copy);
-	cleanup_async_copy(copy);
 	return 0;
 }
 
diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h
index 2a21a7662e03..dec29afa43f3 100644
--- a/fs/nfsd/xdr4.h
+++ b/fs/nfsd/xdr4.h
@@ -699,6 +699,9 @@ struct nfsd4_copy {
 	struct nfsd42_write_res	cp_res;
 	struct knfsd_fh		fh;
 
+	/* offload callback */
+	struct nfsd4_cb_offload	cp_cb_offload;
+
 	struct nfs4_client      *cp_clp;
 
 	struct nfsd_file        *nf_src;
-- 
2.46.2