From: Neil Brown Date: Fri, 6 Jan 2006 08:19:59 +0000 (-0800) Subject: [PATCH] knfsd: reduce stack consumption X-Git-Tag: v2.6.16-rc1~936^2~64 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9f708e40fe040e79f6c393a282f0701c9f8dc174;p=linux-2.6 [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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c index f83ab4cf42..df4019f045 100644 --- 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;