remove_suid bangs on xattrs

[Chris Mason <chris.mason@oracle.com>]

Hi everyone,

I'm looking into a 2.6.35 btrfs performance regression, and perf tells
me that I'm spending a lot of time hammering on xattrs inside
remove_suid.  This is pretty surprising because I'm running as root, and
my files are not suid.  Looking back to this commit:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=b53767719b6cd8789392ea3e7e2eb7b8906898f0

We've changed remove_suid's semantics from

if (file_is_suid)
    try to remove it

To something that always checks to see if we have removal permissions.

Was this intentional?  It didn't cause my 2.6.35 regression (that's all
my fault) but it does look wrong to me:

diff --git a/mm/filemap.c b/mm/filemap.c
index 4fb1546..79f24a9 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1627,12 +1627,18 @@ int __remove_suid(struct dentry *dentry, int kill)
 
 int remove_suid(struct dentry *dentry)
 {
-       int kill = should_remove_suid(dentry);
+       int killsuid = should_remove_suid(dentry);
+       int killpriv = security_inode_need_killpriv(dentry);
+       int error = 0;
 
-       if (unlikely(kill))
-               return __remove_suid(dentry, kill);
+       if (killpriv < 0)
+               return killpriv;
+       if (killpriv)
+               error = security_inode_killpriv(dentry);
+       if (!error && killsuid)
+               error = __remove_suid(dentry, killsuid);
 
-       return 0;
+       return error;
 }
 EXPORT_SYMBOL(remove_suid);

-chris