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authorAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>2010-06-30 19:18:50 +0530
committerEric Van Hensbergen <ericvh@gmail.com>2010-08-02 14:28:35 -0500
commita534c8d15b1f1d0f861fc2bb9e0529bd8486ec3f (patch)
tree0451da7a61bd7e3eb5968d65beee3243f7f51b5d /fs/9p/fid.c
parentebf46264a004818fe5b23f0ac18ac7336897d807 (diff)
downloadlinux-a534c8d15b1f1d0f861fc2bb9e0529bd8486ec3f.tar.bz2
fs/9p: Prevent parallel rename when doing fid_lookup
During fid lookup we need to make sure that the dentry->d_parent doesn't change so that we can safely walk the parent dentries. To ensure that we need to prevent cross directory rename during fid_lookup. Add a per superblock rename_sem rw_semaphore to prevent parallel fid lookup and rename. Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com> Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
Diffstat (limited to 'fs/9p/fid.c')
-rw-r--r--fs/9p/fid.c114
1 files changed, 78 insertions, 36 deletions
diff --git a/fs/9p/fid.c b/fs/9p/fid.c
index 5d6cfcbf73e7..358563689064 100644
--- a/fs/9p/fid.c
+++ b/fs/9p/fid.c
@@ -97,6 +97,34 @@ static struct p9_fid *v9fs_fid_find(struct dentry *dentry, u32 uid, int any)
return ret;
}
+/*
+ * We need to hold v9ses->rename_sem as long as we hold references
+ * to returned path array. Array element contain pointers to
+ * dentry names.
+ */
+static int build_path_from_dentry(struct v9fs_session_info *v9ses,
+ struct dentry *dentry, char ***names)
+{
+ int n = 0, i;
+ char **wnames;
+ struct dentry *ds;
+
+ for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
+ n++;
+
+ wnames = kmalloc(sizeof(char *) * n, GFP_KERNEL);
+ if (!wnames)
+ goto err_out;
+
+ for (ds = dentry, i = (n-1); i >= 0; i--, ds = ds->d_parent)
+ wnames[i] = (char *)ds->d_name.name;
+
+ *names = wnames;
+ return n;
+err_out:
+ return -ENOMEM;
+}
+
/**
* v9fs_fid_lookup - lookup for a fid, try to walk if not found
* @dentry: dentry to look for fid in
@@ -112,7 +140,7 @@ struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
int i, n, l, clone, any, access;
u32 uid;
struct p9_fid *fid, *old_fid = NULL;
- struct dentry *d, *ds;
+ struct dentry *ds;
struct v9fs_session_info *v9ses;
char **wnames, *uname;
@@ -139,50 +167,62 @@ struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
fid = v9fs_fid_find(dentry, uid, any);
if (fid)
return fid;
-
+ /*
+ * we don't have a matching fid. To do a TWALK we need
+ * parent fid. We need to prevent rename when we want to
+ * look at the parent.
+ */
+ down_read(&v9ses->rename_sem);
ds = dentry->d_parent;
fid = v9fs_fid_find(ds, uid, any);
- if (!fid) { /* walk from the root */
- n = 0;
- for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
- n++;
-
- fid = v9fs_fid_find(ds, uid, any);
- if (!fid) { /* the user is not attached to the fs yet */
- if (access == V9FS_ACCESS_SINGLE)
- return ERR_PTR(-EPERM);
-
- if (v9fs_proto_dotu(v9ses) ||
- v9fs_proto_dotl(v9ses))
- uname = NULL;
- else
- uname = v9ses->uname;
+ if (fid) {
+ /* Found the parent fid do a lookup with that */
+ fid = p9_client_walk(fid, 1, (char **)&dentry->d_name.name, 1);
+ goto fid_out;
+ }
+ up_read(&v9ses->rename_sem);
- fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
- v9ses->aname);
+ /* start from the root and try to do a lookup */
+ fid = v9fs_fid_find(dentry->d_sb->s_root, uid, any);
+ if (!fid) {
+ /* the user is not attached to the fs yet */
+ if (access == V9FS_ACCESS_SINGLE)
+ return ERR_PTR(-EPERM);
- if (IS_ERR(fid))
- return fid;
+ if (v9fs_proto_dotu(v9ses) || v9fs_proto_dotl(v9ses))
+ uname = NULL;
+ else
+ uname = v9ses->uname;
- v9fs_fid_add(ds, fid);
- }
- } else /* walk from the parent */
- n = 1;
+ fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
+ v9ses->aname);
+ if (IS_ERR(fid))
+ return fid;
- if (ds == dentry)
+ v9fs_fid_add(dentry->d_sb->s_root, fid);
+ }
+ /* If we are root ourself just return that */
+ if (dentry->d_sb->s_root == dentry)
return fid;
-
- wnames = kmalloc(sizeof(char *) * n, GFP_KERNEL);
- if (!wnames)
- return ERR_PTR(-ENOMEM);
-
- for (d = dentry, i = (n-1); i >= 0; i--, d = d->d_parent)
- wnames[i] = (char *) d->d_name.name;
-
+ /*
+ * Do a multipath walk with attached root.
+ * When walking parent we need to make sure we
+ * don't have a parallel rename happening
+ */
+ down_read(&v9ses->rename_sem);
+ n = build_path_from_dentry(v9ses, dentry, &wnames);
+ if (n < 0) {
+ fid = ERR_PTR(n);
+ goto err_out;
+ }
clone = 1;
i = 0;
while (i < n) {
l = min(n - i, P9_MAXWELEM);
+ /*
+ * We need to hold rename lock when doing a multipath
+ * walk to ensure none of the patch component change
+ */
fid = p9_client_walk(fid, l, &wnames[i], clone);
if (IS_ERR(fid)) {
if (old_fid) {
@@ -194,15 +234,17 @@ struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
p9_client_clunk(old_fid);
}
kfree(wnames);
- return fid;
+ goto err_out;
}
old_fid = fid;
i += l;
clone = 0;
}
-
kfree(wnames);
+fid_out:
v9fs_fid_add(dentry, fid);
+err_out:
+ up_read(&v9ses->rename_sem);
return fid;
}