[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: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index f83ab4cf426503d4b6714035e8b5601817e960c7..df4019f04560d54df1b1c0faa270f18b3afd0d40 100644 (file)
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -880,6 +880,16 @@ out:
        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;