[PATCH] 9p: fix segfault caused by race condition in meta-data operations

Running dbench multithreaded exposed a race condition where fid structures
were removed while in use.  This patch adds semaphores to meta-data operations
to protect the fid structure.  Some cleanup of error-case handling in the
inode operations is also included.

Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 196 insertions, 129 deletions

diff --git a/fs/9p/fid.c b/fs/9p/fid.c
index 27507201f9e7..a9b6301a04fc 100644
--- a/fs/9p/fid.c
+++ b/fs/9p/fid.c
@@ -25,6 +25,7 @@
 #include <linux/fs.h>
 #include <linux/sched.h>
 #include <linux/idr.h>
+#include <asm/semaphore.h>
 
 #include "debug.h"
 #include "v9fs.h"
@@ -84,6 +85,7 @@ struct v9fs_fid *v9fs_fid_create(struct v9fs_session_info *v9ses, int fid)
         new->iounit = 0;
         new->rdir_pos = 0;
         new->rdir_fcall = NULL;
+        init_MUTEX(&new->lock);
         INIT_LIST_HEAD(&new->list);
 
         return new;
@@ -102,11 +104,11 @@ void v9fs_fid_destroy(struct v9fs_fid *fid)
 }
 
 /**
- * v9fs_fid_lookup - retrieve the right fid from a  particular dentry
+ * v9fs_fid_lookup - return a locked fid from a dentry
  * @dentry: dentry to look for fid in
- * @type: intent of lookup (operation or traversal)
  *
- * find a fid in the dentry
+ * find a fid in the dentry, obtain its semaphore and return a reference to it.
+ * code calling lookup is responsible for releasing lock
  *
  * TODO: only match fids that have the same uid as current user
  *
@@ -124,7 +126,68 @@ struct v9fs_fid *v9fs_fid_lookup(struct dentry *dentry)
 
         if (!return_fid) {
                 dprintk(DEBUG_ERROR, "Couldn't find a fid in dentry\n");
+                return_fid = ERR_PTR(-EBADF);
         }
 
+        if(down_interruptible(&return_fid->lock))
+                return ERR_PTR(-EINTR);
+
         return return_fid;
 }
+
+/**
+ * v9fs_fid_clone - lookup the fid for a dentry, clone a private copy and release it
+ * @dentry: dentry to look for fid in
+ *
+ * find a fid in the dentry and then clone to a new private fid
+ *
+ * TODO: only match fids that have the same uid as current user
+ *
+ */
+
+struct v9fs_fid *v9fs_fid_clone(struct dentry *dentry)
+{
+        struct v9fs_session_info *v9ses = v9fs_inode2v9ses(dentry->d_inode);
+        struct v9fs_fid *base_fid, *new_fid = ERR_PTR(-EBADF);
+        struct v9fs_fcall *fcall = NULL;
+        int fid, err;
+
+        base_fid = v9fs_fid_lookup(dentry);
+
+        if(IS_ERR(base_fid))
+                return base_fid;
+
+        if(base_fid) {  /* clone fid */
+                fid = v9fs_get_idpool(&v9ses->fidpool);
+                if (fid < 0) {
+                        eprintk(KERN_WARNING, "newfid fails!\n");
+                        new_fid = ERR_PTR(-ENOSPC);
+                        goto Release_Fid;
+                }
+
+                err = v9fs_t_walk(v9ses, base_fid->fid, fid, NULL, &fcall);
+                if (err < 0) {
+                        dprintk(DEBUG_ERROR, "clone walk didn't work\n");
+                        v9fs_put_idpool(fid, &v9ses->fidpool);
+                        new_fid = ERR_PTR(err);
+                        goto Free_Fcall;
+                }
+                new_fid = v9fs_fid_create(v9ses, fid);
+                if (new_fid == NULL) {
+                        dprintk(DEBUG_ERROR, "out of memory\n");
+                        new_fid = ERR_PTR(-ENOMEM);
+                }
+Free_Fcall:
+                kfree(fcall);
+        }
+
+Release_Fid:
+        up(&base_fid->lock);
+        return new_fid;
+}
+
+void v9fs_fid_clunk(struct v9fs_session_info *v9ses, struct v9fs_fid *fid)
+{
+        v9fs_t_clunk(v9ses, fid->fid);
+        v9fs_fid_destroy(fid);
+}
diff --git a/fs/9p/fid.h b/fs/9p/fid.h
index aa974d6875c3..48fc170c26c8 100644
--- a/fs/9p/fid.h
+++ b/fs/9p/fid.h
@@ -30,6 +30,8 @@ struct v9fs_fid {
         struct list_head list;   /* list of fids associated with a dentry */
         struct list_head active; /* XXX - debug */
 
+        struct semaphore lock;
+
         u32 fid;
         unsigned char fidopen;    /* set when fid is opened */
         unsigned char fidclunked; /* set when fid has already been clunked */
@@ -55,3 +57,6 @@ struct v9fs_fid *v9fs_fid_get_created(struct dentry *);
 void v9fs_fid_destroy(struct v9fs_fid *fid);
 struct v9fs_fid *v9fs_fid_create(struct v9fs_session_info *, int fid);
 int v9fs_fid_insert(struct v9fs_fid *fid, struct dentry *dentry);
+struct v9fs_fid *v9fs_fid_clone(struct dentry *dentry);
+void v9fs_fid_clunk(struct v9fs_session_info *v9ses, struct v9fs_fid *fid);
+
diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index e86a07151280..9f17b0cacdd0 100644
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -55,53 +55,22 @@ int v9fs_file_open(struct inode *inode, struct file *file)
         struct v9fs_fid *vfid;
         struct v9fs_fcall *fcall = NULL;
         int omode;
-        int fid = V9FS_NOFID;
         int err;
 
         dprintk(DEBUG_VFS, "inode: %p file: %p \n", inode, file);
 
-        vfid = v9fs_fid_lookup(file->f_path.dentry);
-        if (!vfid) {
-                dprintk(DEBUG_ERROR, "Couldn't resolve fid from dentry\n");
-                return -EBADF;
-        }
-
-        fid = v9fs_get_idpool(&v9ses->fidpool);
-        if (fid < 0) {
-                eprintk(KERN_WARNING, "newfid fails!\n");
-                return -ENOSPC;
-        }
+        vfid = v9fs_fid_clone(file->f_path.dentry);
+        if (IS_ERR(vfid))
+                return PTR_ERR(vfid);
 
-        err = v9fs_t_walk(v9ses, vfid->fid, fid, NULL, &fcall);
-        if (err < 0) {
-                dprintk(DEBUG_ERROR, "rewalk didn't work\n");
-                if (fcall && fcall->id == RWALK)
-                        goto clunk_fid;
-                else {
-                        v9fs_put_idpool(fid, &v9ses->fidpool);
-                        goto free_fcall;
-                }
-        }
-        kfree(fcall);
-
-        /* TODO: do special things for O_EXCL, O_NOFOLLOW, O_SYNC */
-        /* translate open mode appropriately */
         omode = v9fs_uflags2omode(file->f_flags);
-        err = v9fs_t_open(v9ses, fid, omode, &fcall);
+        err = v9fs_t_open(v9ses, vfid->fid, omode, &fcall);
         if (err < 0) {
                 PRINT_FCALL_ERROR("open failed", fcall);
-                goto clunk_fid;
-        }
-
-        vfid = kmalloc(sizeof(struct v9fs_fid), GFP_KERNEL);
-        if (vfid == NULL) {
-                dprintk(DEBUG_ERROR, "out of memory\n");
-                err = -ENOMEM;
-                goto clunk_fid;
+                goto Clunk_Fid;
         }
 
         file->private_data = vfid;
-        vfid->fid = fid;
         vfid->fidopen = 1;
         vfid->fidclunked = 0;
         vfid->iounit = fcall->params.ropen.iounit;
@@ -112,10 +81,8 @@ int v9fs_file_open(struct inode *inode, struct file *file)
 
         return 0;
 
-clunk_fid:
-        v9fs_t_clunk(v9ses, fid);
-
-free_fcall:
+Clunk_Fid:
+        v9fs_fid_clunk(v9ses, vfid);
         kfree(fcall);
 
         return err;
diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index 05d30e89ba45..9109ba1d6969 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -416,12 +416,8 @@ static int v9fs_remove(struct inode *dir, struct dentry *file, int rmdir)
         sb = file_inode->i_sb;
         v9ses = v9fs_inode2v9ses(file_inode);
         v9fid = v9fs_fid_lookup(file);
-
-        if (!v9fid) {
-                dprintk(DEBUG_ERROR,
-                        "no v9fs_fid\n");
-                return -EBADF;
-        }
+        if(IS_ERR(v9fid))
+                return PTR_ERR(v9fid);
 
         fid = v9fid->fid;
         if (fid < 0) {
@@ -433,11 +429,13 @@ static int v9fs_remove(struct inode *dir, struct dentry *file, int rmdir)
         result = v9fs_t_remove(v9ses, fid, &fcall);
         if (result < 0) {
                 PRINT_FCALL_ERROR("remove fails", fcall);
+                goto Error;
         }
 
         v9fs_put_idpool(fid, &v9ses->fidpool);
         v9fs_fid_destroy(v9fid);
 
+Error:
         kfree(fcall);
         return result;
 }
@@ -473,9 +471,13 @@ v9fs_vfs_create(struct inode *dir, struct dentry *dentry, int mode,
         inode = NULL;
         vfid = NULL;
         v9ses = v9fs_inode2v9ses(dir);
-        dfid = v9fs_fid_lookup(dentry->d_parent);
-        perm = unixmode2p9mode(v9ses, mode);
+        dfid = v9fs_fid_clone(dentry->d_parent);
+        if(IS_ERR(dfid)) {
+                err = PTR_ERR(dfid);
+                goto error;
+        }
 
+        perm = unixmode2p9mode(v9ses, mode);
         if (nd && nd->flags & LOOKUP_OPEN)
                 flags = nd->intent.open.flags - 1;
         else
@@ -485,9 +487,10 @@ v9fs_vfs_create(struct inode *dir, struct dentry *dentry, int mode,
                 perm, v9fs_uflags2omode(flags), NULL, &fid, &qid, &iounit);
 
         if (err)
-                goto error;
+                goto clunk_dfid;
 
         vfid = v9fs_clone_walk(v9ses, dfid->fid, dentry);
+        v9fs_fid_clunk(v9ses, dfid);
         if (IS_ERR(vfid)) {
                 err = PTR_ERR(vfid);
                 vfid = NULL;
@@ -525,6 +528,9 @@ v9fs_vfs_create(struct inode *dir, struct dentry *dentry, int mode,
 
         return 0;
 
+clunk_dfid:
+        v9fs_fid_clunk(v9ses, dfid);
+
 error:
         if (vfid)
                 v9fs_fid_destroy(vfid);
@@ -551,7 +557,12 @@ static int v9fs_vfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
         inode = NULL;
         vfid = NULL;
         v9ses = v9fs_inode2v9ses(dir);
-        dfid = v9fs_fid_lookup(dentry->d_parent);
+        dfid = v9fs_fid_clone(dentry->d_parent);
+        if(IS_ERR(dfid)) {
+                err = PTR_ERR(dfid);
+                goto error;
+        }
+
         perm = unixmode2p9mode(v9ses, mode | S_IFDIR);
 
         err = v9fs_create(v9ses, dfid->fid, (char *) dentry->d_name.name,
@@ -559,37 +570,36 @@ static int v9fs_vfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
 
         if (err) {
                 dprintk(DEBUG_ERROR, "create error %d\n", err);
-                goto error;
-        }
-
-        err = v9fs_t_clunk(v9ses, fid);
-        if (err) {
-                dprintk(DEBUG_ERROR, "clunk error %d\n", err);
-                goto error;
+                goto clean_up_dfid;
         }
 
         vfid = v9fs_clone_walk(v9ses, dfid->fid, dentry);
         if (IS_ERR(vfid)) {
                 err = PTR_ERR(vfid);
                 vfid = NULL;
-                goto error;
+                goto clean_up_dfid;
         }
 
+        v9fs_fid_clunk(v9ses, dfid);
         inode = v9fs_inode_from_fid(v9ses, vfid->fid, dir->i_sb);
         if (IS_ERR(inode)) {
                 err = PTR_ERR(inode);
                 inode = NULL;
-                goto error;
+                goto clean_up_fids;
         }
 
         dentry->d_op = &v9fs_dentry_operations;
         d_instantiate(dentry, inode);
         return 0;
 
-error:
+clean_up_fids:
         if (vfid)
                 v9fs_fid_destroy(vfid);
 
+clean_up_dfid:
+        v9fs_fid_clunk(v9ses, dfid);
+
+error:
         return err;
 }
 
@@ -622,28 +632,23 @@ static struct dentry *v9fs_vfs_lookup(struct inode *dir, struct dentry *dentry,
         dentry->d_op = &v9fs_dentry_operations;
         dirfid = v9fs_fid_lookup(dentry->d_parent);
 
-        if (!dirfid) {
-                dprintk(DEBUG_ERROR, "no dirfid\n");
-                return ERR_PTR(-EINVAL);
-        }
+        if(IS_ERR(dirfid))
+                return ERR_PTR(PTR_ERR(dirfid));
 
         dirfidnum = dirfid->fid;
 
-        if (dirfidnum < 0) {
-                dprintk(DEBUG_ERROR, "no dirfid for inode %p, #%lu\n",
-                        dir, dir->i_ino);
-                return ERR_PTR(-EBADF);
-        }
-
         newfid = v9fs_get_idpool(&v9ses->fidpool);
         if (newfid < 0) {
                 eprintk(KERN_WARNING, "newfid fails!\n");
-                return ERR_PTR(-ENOSPC);
+                result = -ENOSPC;
+                goto Release_Dirfid;
         }
 
         result = v9fs_t_walk(v9ses, dirfidnum, newfid,
                 (char *)dentry->d_name.name, &fcall);
 
+        up(&dirfid->lock);
+
         if (result < 0) {
                 if (fcall && fcall->id == RWALK)
                         v9fs_t_clunk(v9ses, newfid);
@@ -701,8 +706,12 @@ static struct dentry *v9fs_vfs_lookup(struct inode *dir, struct dentry *dentry,
 
         return NULL;
 
-      FreeFcall:
+Release_Dirfid:
+        up(&dirfid->lock);
+
+FreeFcall:
         kfree(fcall);
+
         return ERR_PTR(result);
 }
 
@@ -746,10 +755,8 @@ v9fs_vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
         struct inode *old_inode = old_dentry->d_inode;
         struct v9fs_session_info *v9ses = v9fs_inode2v9ses(old_inode);
         struct v9fs_fid *oldfid = v9fs_fid_lookup(old_dentry);
-        struct v9fs_fid *olddirfid =
-            v9fs_fid_lookup(old_dentry->d_parent);
-        struct v9fs_fid *newdirfid =
-            v9fs_fid_lookup(new_dentry->d_parent);
+        struct v9fs_fid *olddirfid;
+        struct v9fs_fid *newdirfid;
         struct v9fs_wstat wstat;
         struct v9fs_fcall *fcall = NULL;
         int fid = -1;
@@ -759,16 +766,26 @@ v9fs_vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 
         dprintk(DEBUG_VFS, "\n");
 
-        if ((!oldfid) || (!olddirfid) || (!newdirfid)) {
-                dprintk(DEBUG_ERROR, "problem with arguments\n");
-                return -EBADF;
+        if(IS_ERR(oldfid))
+                return PTR_ERR(oldfid);
+
+        olddirfid = v9fs_fid_clone(old_dentry->d_parent);
+        if(IS_ERR(olddirfid)) {
+                retval = PTR_ERR(olddirfid);
+                goto Release_lock;
+        }
+
+        newdirfid = v9fs_fid_clone(new_dentry->d_parent);
+        if(IS_ERR(newdirfid)) {
+                retval = PTR_ERR(newdirfid);
+                goto Clunk_olddir;
         }
 
         /* 9P can only handle file rename in the same directory */
         if (memcmp(&olddirfid->qid, &newdirfid->qid, sizeof(newdirfid->qid))) {
                 dprintk(DEBUG_ERROR, "old dir and new dir are different\n");
                 retval = -EXDEV;
-                goto FreeFcallnBail;
+                goto Clunk_newdir;
         }
 
         fid = oldfid->fid;
@@ -779,7 +796,7 @@ v9fs_vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
                 dprintk(DEBUG_ERROR, "no fid for old file #%lu\n",
                         old_inode->i_ino);
                 retval = -EBADF;
-                goto FreeFcallnBail;
+                goto Clunk_newdir;
         }
 
         v9fs_blank_wstat(&wstat);
@@ -788,11 +805,20 @@ v9fs_vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 
         retval = v9fs_t_wstat(v9ses, fid, &wstat, &fcall);
 
-      FreeFcallnBail:
         if (retval < 0)
                 PRINT_FCALL_ERROR("wstat error", fcall);
 
         kfree(fcall);
+
+Clunk_newdir:
+        v9fs_fid_clunk(v9ses, newdirfid);
+
+Clunk_olddir:
+        v9fs_fid_clunk(v9ses, olddirfid);
+
+Release_lock:
+        up(&oldfid->lock);
+
         return retval;
 }
 
@@ -810,15 +836,12 @@ v9fs_vfs_getattr(struct vfsmount *mnt, struct dentry *dentry,
 {
         struct v9fs_fcall *fcall = NULL;
         struct v9fs_session_info *v9ses = v9fs_inode2v9ses(dentry->d_inode);
-        struct v9fs_fid *fid = v9fs_fid_lookup(dentry);
+        struct v9fs_fid *fid = v9fs_fid_clone(dentry);
         int err = -EPERM;
 
         dprintk(DEBUG_VFS, "dentry: %p\n", dentry);
-        if (!fid) {
-                dprintk(DEBUG_ERROR,
-                        "couldn't find fid associated with dentry\n");
-                return -EBADF;
-        }
+        if(IS_ERR(fid))
+                return PTR_ERR(fid);
 
         err = v9fs_t_stat(v9ses, fid->fid, &fcall);
 
@@ -831,6 +854,7 @@ v9fs_vfs_getattr(struct vfsmount *mnt, struct dentry *dentry,
         }
 
         kfree(fcall);
+        v9fs_fid_clunk(v9ses, fid);
         return err;
 }
 
@@ -844,18 +868,14 @@ v9fs_vfs_getattr(struct vfsmount *mnt, struct dentry *dentry,
 static int v9fs_vfs_setattr(struct dentry *dentry, struct iattr *iattr)
 {
         struct v9fs_session_info *v9ses = v9fs_inode2v9ses(dentry->d_inode);
-        struct v9fs_fid *fid = v9fs_fid_lookup(dentry);
+        struct v9fs_fid *fid = v9fs_fid_clone(dentry);
         struct v9fs_fcall *fcall = NULL;
         struct v9fs_wstat wstat;
         int res = -EPERM;
 
         dprintk(DEBUG_VFS, "\n");
-
-        if (!fid) {
-                dprintk(DEBUG_ERROR,
-                        "Couldn't find fid associated with dentry\n");
-                return -EBADF;
-        }
+        if(IS_ERR(fid))
+                return PTR_ERR(fid);
 
         v9fs_blank_wstat(&wstat);
         if (iattr->ia_valid & ATTR_MODE)
@@ -887,6 +907,7 @@ static int v9fs_vfs_setattr(struct dentry *dentry, struct iattr *iattr)
         if (res >= 0)
                 res = inode_setattr(dentry->d_inode, iattr);
 
+        v9fs_fid_clunk(v9ses, fid);
         return res;
 }
 
@@ -987,18 +1008,15 @@ static int v9fs_readlink(struct dentry *dentry, char *buffer, int buflen)
 
         struct v9fs_fcall *fcall = NULL;
         struct v9fs_session_info *v9ses = v9fs_inode2v9ses(dentry->d_inode);
-        struct v9fs_fid *fid = v9fs_fid_lookup(dentry);
+        struct v9fs_fid *fid = v9fs_fid_clone(dentry);
 
-        if (!fid) {
-                dprintk(DEBUG_ERROR, "could not resolve fid from dentry\n");
-                retval = -EBADF;
-                goto FreeFcall;
-        }
+        if(IS_ERR(fid))
+                return PTR_ERR(fid);
 
         if (!v9ses->extended) {
                 retval = -EBADF;
                 dprintk(DEBUG_ERROR, "not extended\n");
-                goto FreeFcall;
+                goto ClunkFid;
         }
 
         dprintk(DEBUG_VFS, " %s\n", dentry->d_name.name);
@@ -1009,8 +1027,10 @@ static int v9fs_readlink(struct dentry *dentry, char *buffer, int buflen)
                 goto FreeFcall;
         }
 
-        if (!fcall)
-                return -EIO;
+        if (!fcall) {
+                retval = -EIO;
+                goto ClunkFid;
+        }
 
         if (!(fcall->params.rstat.stat.mode & V9FS_DMSYMLINK)) {
                 retval = -EINVAL;
@@ -1028,9 +1048,12 @@ static int v9fs_readlink(struct dentry *dentry, char *buffer, int buflen)
                 fcall->params.rstat.stat.extension.str, buffer);
         retval = buflen;
 
-      FreeFcall:
+FreeFcall:
         kfree(fcall);
 
+ClunkFid:
+        v9fs_fid_clunk(v9ses, fid);
+
         return retval;
 }
 
@@ -1123,52 +1146,58 @@ static int v9fs_vfs_mkspecial(struct inode *dir, struct dentry *dentry,
         int err;
         u32 fid, perm;
         struct v9fs_session_info *v9ses;
-        struct v9fs_fid *dfid, *vfid;
-        struct inode *inode;
+        struct v9fs_fid *dfid, *vfid = NULL;
+        struct inode *inode = NULL;
 
-        inode = NULL;
-        vfid = NULL;
         v9ses = v9fs_inode2v9ses(dir);
-        dfid = v9fs_fid_lookup(dentry->d_parent);
-        perm = unixmode2p9mode(v9ses, mode);
-
         if (!v9ses->extended) {
                 dprintk(DEBUG_ERROR, "not extended\n");
                 return -EPERM;
         }
 
+        dfid = v9fs_fid_clone(dentry->d_parent);
+        if(IS_ERR(dfid)) {
+                err = PTR_ERR(dfid);
+                goto error;
+        }
+
+        perm = unixmode2p9mode(v9ses, mode);
+
         err = v9fs_create(v9ses, dfid->fid, (char *) dentry->d_name.name,
                 perm, V9FS_OREAD, (char *) extension, &fid, NULL, NULL);
 
         if (err)
-                goto error;
+                goto clunk_dfid;
 
         err = v9fs_t_clunk(v9ses, fid);
         if (err)
-                goto error;
+                goto clunk_dfid;
 
         vfid = v9fs_clone_walk(v9ses, dfid->fid, dentry);
         if (IS_ERR(vfid)) {
                 err = PTR_ERR(vfid);
                 vfid = NULL;
-                goto error;
+                goto clunk_dfid;
         }
 
         inode = v9fs_inode_from_fid(v9ses, vfid->fid, dir->i_sb);
         if (IS_ERR(inode)) {
                 err = PTR_ERR(inode);
                 inode = NULL;
-                goto error;
+                goto free_vfid;
         }
 
         dentry->d_op = &v9fs_dentry_operations;
         d_instantiate(dentry, inode);
         return 0;
 
-error:
-        if (vfid)
-                v9fs_fid_destroy(vfid);
+free_vfid:
+        v9fs_fid_destroy(vfid);
+
+clunk_dfid:
+        v9fs_fid_clunk(v9ses, dfid);
 
+error:
         return err;
 
 }
@@ -1209,26 +1238,29 @@ v9fs_vfs_link(struct dentry *old_dentry, struct inode *dir,
               struct dentry *dentry)
 {
         int retval;
+        struct v9fs_session_info *v9ses = v9fs_inode2v9ses(dir);
         struct v9fs_fid *oldfid;
         char *name;
 
         dprintk(DEBUG_VFS, " %lu,%s,%s\n", dir->i_ino, dentry->d_name.name,
                 old_dentry->d_name.name);
 
-        oldfid = v9fs_fid_lookup(old_dentry);
-        if (!oldfid) {
-                dprintk(DEBUG_ERROR, "can't find oldfid\n");
-                return -EPERM;
-        }
+        oldfid = v9fs_fid_clone(old_dentry);
+        if(IS_ERR(oldfid))
+                return PTR_ERR(oldfid);
 
         name = __getname();
-        if (unlikely(!name))
-                return -ENOMEM;
+        if (unlikely(!name)) {
+                retval = -ENOMEM;
+                goto clunk_fid;
+        }
 
         sprintf(name, "%d\n", oldfid->fid);
         retval = v9fs_vfs_mkspecial(dir, dentry, V9FS_DMLINK, name);
         __putname(name);
 
+clunk_fid:
+        v9fs_fid_clunk(v9ses, oldfid);
         return retval;
 }