From: Jeff Layton <jlayton@redhat.com>
Subject: [RHEL5 PATCH] RPC: when downsizing response buffer, account for 	checksum (BZ 238687)
Date: Mon, 7 May 2007 18:02:41 -0400
Bugzilla: 238687
Message-Id: <20070507220241.GH6129@dantu.rdu.redhat.com>
Changelog: [nfs] RPC: when downsizing response buffer, account for checksum


Currently, when the RPC layer is building a response it calls svc_reserve to
downsize the reservation in the response buffer. The size that it uses in this
situation does not account for the possibility of a checksum at the end of
the packet.

This is mostly evident when mounting NFSv2/3 with sec=krb5i or sec=krb5p. When
you do this and do a bunch of I/O to the filesystem, you'll get printk's that
look something like this:

	RPC request reserved 164 but used 208

NFSv4 seems to have a large enough reserved size for compound packets that it
usually papers over this problem.

These are soft reservations, and overflowing them generally isn't harmful,
but this can generate a lot of printk spam on a busy mount. The following
patch is a backport of the patch I've sent upstream to resolve this. The
upstream patch is currently in -mm.

diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index f61142a..7d47c16 100644
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -175,7 +175,7 @@ nfsd3_proc_read(struct svc_rqst *rqstp, struct nfsd3_readargs *argp,
 	if (NFSSVC_MAXBLKSIZE < resp->count)
 		resp->count = NFSSVC_MAXBLKSIZE;
 
-	svc_reserve(rqstp, ((1 + NFS3_POST_OP_ATTR_WORDS + 3)<<2) + resp->count +4);
+	svc_reserve_auth(rqstp, ((1 + NFS3_POST_OP_ATTR_WORDS + 3)<<2) + resp->count +4);
 
 	fh_copy(&resp->fh, &argp->fh);
 	nfserr = nfsd_read(rqstp, &resp->fh, NULL,
diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
index 4e06810..21f2ff7 100644
--- a/fs/nfsd/nfsproc.c
+++ b/fs/nfsd/nfsproc.c
@@ -154,7 +154,7 @@ nfsd_proc_read(struct svc_rqst *rqstp, struct nfsd_readargs *argp,
 				argp->count);
 		argp->count = NFSSVC_MAXBLKSIZE;
 	}
-	svc_reserve(rqstp, (19<<2) + argp->count + 4);
+	svc_reserve_auth(rqstp, (19<<2) + argp->count + 4);
 
 	resp->count = argp->count;
 	nfserr = nfsd_read(rqstp, fh_copy(&resp->fh, &argp->fh), NULL,
diff --git a/include/linux/sunrpc/auth.h b/include/linux/sunrpc/auth.h
index a6de332..d7cf890 100644
--- a/include/linux/sunrpc/auth.h
+++ b/include/linux/sunrpc/auth.h
@@ -20,9 +20,6 @@
 /* size of the nodename buffer */
 #define UNX_MAXNODENAME	32
 
-/* Maximum size (in bytes) of an rpc credential or verifier */
-#define RPC_MAX_AUTH_SIZE (400)
-
 /* Work around the lack of a VFS credential */
 struct auth_cred {
 	uid_t	uid;
diff --git a/include/linux/sunrpc/msg_prot.h b/include/linux/sunrpc/msg_prot.h
index f43f237..a519176 100644
--- a/include/linux/sunrpc/msg_prot.h
+++ b/include/linux/sunrpc/msg_prot.h
@@ -34,6 +34,9 @@ enum rpc_auth_flavors {
 	RPC_AUTH_GSS_SPKMP = 390011,
 };
 
+/* Maximum size (in bytes) of an rpc credential or verifier */
+#define RPC_MAX_AUTH_SIZE (400)
+
 enum rpc_msg_type {
 	RPC_CALL = 0,
 	RPC_REPLY = 1
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 94350f5..486abfe 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -326,4 +326,23 @@ int		   svc_register(struct svc_serv *, int, unsigned short);
 void		   svc_wake_up(struct svc_serv *);
 void		   svc_reserve(struct svc_rqst *rqstp, int space);
 
+/*
+ * When we want to reduce the size of the reserved space in the response
+ * buffer, we need to take into account the size of any checksum data that
+ * may be at the end of the packet. This is difficult to determine exactly
+ * for all cases without actually generating the checksum, so we just use a
+ * static value.
+ */
+static inline void 
+svc_reserve_auth(struct svc_rqst *rqstp, int space)
+{
+	int			added_space = 0;
+
+	switch(rqstp->rq_authop->flavour) {
+		case RPC_AUTH_GSS:
+			added_space = RPC_MAX_AUTH_SIZE;
+	}
+	return svc_reserve(rqstp, space + added_space);
+}
+
 #endif /* SUNRPC_SVC_H */
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 0aab5b5..2d390d1 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -379,7 +379,7 @@ svc_process(struct svc_serv *serv, struct svc_rqst *rqstp)
 	 * better idea of reply size
 	 */
 	if (procp->pc_xdrressize)
-		svc_reserve(rqstp, procp->pc_xdrressize<<2);
+		svc_reserve_auth(rqstp, procp->pc_xdrressize<<2);
 
 	/* Call the function that processes the request. */
 	if (!versp->vs_dispatch) {