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authorJ. Bruce Fields <bfields@redhat.com>2013-10-17 21:34:21 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2013-11-09 00:16:38 -0500
commitf27c9298fd717e1f7e63e314a7a85a3a7e77139d (patch)
treeba217e7745e5c0d7e0279a5d7ddb79cb1a03662b /fs/exportfs
parentefbf201f7a0be7ffc6532e672fbccb0eed4f5de0 (diff)
downloadlinux-stericsson-f27c9298fd717e1f7e63e314a7a85a3a7e77139d.tar.gz
exportfs: fix quadratic behavior in filehandle lookup
Suppose we're given the filehandle for a directory whose closest ancestor in the dcache is its Nth ancestor. The main loop in reconnect_path searches for an IS_ROOT ancestor of target_dir, reconnects that ancestor to its parent, then recommences the search for an IS_ROOT ancestor from target_dir. This behavior is quadratic in N. And there's really no need to restart the search from target_dir each time: once a directory has been looked up, it won't become IS_ROOT again. So instead of starting from target_dir each time, we can continue where we left off. This simplifies the code and improves performance on very deep directory heirachies. (I can't think of any reason anyone should need heirarchies a hundred or more deep, but the performance improvement may be valuable if only to limit damage in case of abuse.) Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: J. Bruce Fields <bfields@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/exportfs')
-rw-r--r--fs/exportfs/expfs.c66
1 files changed, 13 insertions, 53 deletions
diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
index b33b9c4deea0..48a359dd286e 100644
--- a/fs/exportfs/expfs.c
+++ b/fs/exportfs/expfs.c
@@ -69,27 +69,6 @@ find_acceptable_alias(struct dentry *result,
return NULL;
}
-/*
- * Find root of a disconnected subtree and return a reference to it.
- */
-static struct dentry *
-find_disconnected_root(struct dentry *dentry)
-{
- dget(dentry);
- while (!IS_ROOT(dentry)) {
- struct dentry *parent = dget_parent(dentry);
-
- if (!(parent->d_flags & DCACHE_DISCONNECTED)) {
- dput(parent);
- break;
- }
-
- dput(dentry);
- dentry = parent;
- }
- return dentry;
-}
-
static bool dentry_connected(struct dentry *dentry)
{
dget(dentry);
@@ -225,45 +204,26 @@ out_reconnected:
static int
reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
{
- int err = -ESTALE;
+ struct dentry *dentry, *parent;
- while (target_dir->d_flags & DCACHE_DISCONNECTED) {
- struct dentry *dentry = find_disconnected_root(target_dir);
+ dentry = dget(target_dir);
+ while (dentry->d_flags & DCACHE_DISCONNECTED) {
BUG_ON(dentry == mnt->mnt_sb->s_root);
- if (!IS_ROOT(dentry)) {
- /* must have found a connected parent - great */
- clear_disconnected(target_dir);
- dput(dentry);
+ if (IS_ROOT(dentry))
+ parent = reconnect_one(mnt, dentry, nbuf);
+ else
+ parent = dget_parent(dentry);
+
+ if (!parent)
break;
- } else {
- struct dentry *parent;
- /*
- * We have hit the top of a disconnected path, try to
- * find parent and connect.
- */
- parent = reconnect_one(mnt, dentry, nbuf);
- if (!parent)
- goto out_reconnected;
- if (IS_ERR(parent)) {
- err = PTR_ERR(parent);
- break;
- }
- dput(parent);
- }
dput(dentry);
+ if (IS_ERR(parent))
+ return PTR_ERR(parent);
+ dentry = parent;
}
-
- if (target_dir->d_flags & DCACHE_DISCONNECTED) {
- /* something went wrong - oh-well */
- if (!err)
- err = -ESTALE;
- return err;
- }
-
- return 0;
-out_reconnected:
+ dput(dentry);
clear_disconnected(target_dir);
return 0;
}