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Commit 9f708e40 authored by Neil Brown's avatar Neil Brown Committed by Linus Torvalds
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[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: default avatarNeil Brown <neilb@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent a334de28

fs/nfsd/vfs.c

+12 −8
Original line number Diff line number Diff line
@@ -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;