[PATCH] knfsd: reduce stack consumption

A typical nfsd call trace is
 nfsd -> svc_process -> nfsd_dispatch -> nfsd3_proc_write ->
   nfsd_write ->nfsd_vfs_write -> vfs_writev

These add up to over 300 bytes on the stack.
Looking at each of these, I see that nfsd_write (which includes
 nfsd_vfs_write) contributes 0x8c to stack usage itself!!

It turns out this is because it puts a 'struct iattr' on the stack so
it can kill suid if needed.  The following patch saves about 50 bytes
off the stack in this call path.
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

fs/nfsd/vfs.c

@@ -880,6 +880,16 @@ nfsd_vfs_read(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
 	return err;
 }
 
+static void kill_suid(struct dentry *dentry)
+{
+	struct iattr	ia;
+	ia.ia_valid = ATTR_KILL_SUID | ATTR_KILL_SGID;
+
+	down(&dentry->d_inode->i_sem);
+	notify_change(dentry, &ia);
+	up(&dentry->d_inode->i_sem);
+}
+
 static inline int
 nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
 				loff_t offset, struct kvec *vec, int vlen,
@@ -933,14 +943,8 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
 	}
 
 	/* clear setuid/setgid flag after write */
-	if (err >= 0 && (inode->i_mode & (S_ISUID | S_ISGID))) {
-		struct iattr	ia;
-		ia.ia_valid = ATTR_KILL_SUID | ATTR_KILL_SGID;
-
-		down(&inode->i_sem);
-		notify_change(dentry, &ia);
-		up(&inode->i_sem);
-	}
+	if (err >= 0 && (inode->i_mode & (S_ISUID | S_ISGID)))
+		kill_suid(dentry);
 
 	if (err >= 0 && stable) {
 		static ino_t	last_ino;