[PATCH] v9fs: fix races in fid allocation

Fid management cleanup.  The patch attempts to fix the races in dentry's
fid management.

Dentries don't keep the opened fids anymore, they are moved to the file
structs.  Ideally there should be no more than one fid with fidcreate equal
to zero in the dentry's list of fids.

v9fs_fid_create initializes the important fields (fid, fidcreated) before
v9fs_fid is added to the list.  v9fs_fid_lookup returns only fids that are
not created by v9fs_create.  v9fs_fid_get_created returns the fid created
by the same process by v9fs_create (if any) and removes it from dentry's
list

Signed-off-by: Latchesar Ionkov <lucho@ionkov.net>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 95 insertions, 81 deletions

diff --git a/fs/9p/fid.c b/fs/9p/fid.c
index 821c9c4d76a..d95f8626d17 100644
--- a/fs/9p/fid.c
+++ b/fs/9p/fid.c
@@ -71,21 +71,28 @@ static int v9fs_fid_insert(struct v9fs_fid *fid, struct dentry *dentry)
  *
  */
 
-struct v9fs_fid *v9fs_fid_create(struct dentry *dentry)
+struct v9fs_fid *v9fs_fid_create(struct dentry *dentry,
+	struct v9fs_session_info *v9ses, int fid, int create)
 {
 	struct v9fs_fid *new;
 
+	dprintk(DEBUG_9P, "fid create dentry %p, fid %d, create %d\n",
+		dentry, fid, create);
+
 	new = kmalloc(sizeof(struct v9fs_fid), GFP_KERNEL);
 	if (new == NULL) {
 		dprintk(DEBUG_ERROR, "Out of Memory\n");
 		return ERR_PTR(-ENOMEM);
 	}
 
-	new->fid = -1;
+	new->fid = fid;
+	new->v9ses = v9ses;
 	new->fidopen = 0;
-	new->fidcreate = 0;
+	new->fidcreate = create;
 	new->fidclunked = 0;
 	new->iounit = 0;
+	new->rdir_pos = 0;
+	new->rdir_fcall = NULL;
 
 	if (v9fs_fid_insert(new, dentry) == 0)
 		return new;
@@ -109,6 +116,59 @@ void v9fs_fid_destroy(struct v9fs_fid *fid)
 }
 
 /**
+ * v9fs_fid_walk_up - walks from the process current directory
+ * 	up to the specified dentry.
+ */
+static struct v9fs_fid *v9fs_fid_walk_up(struct dentry *dentry)
+{
+	int fidnum, cfidnum, err;
+	struct v9fs_fid *cfid;
+	struct dentry *cde;
+	struct v9fs_session_info *v9ses;
+
+	v9ses = v9fs_inode2v9ses(current->fs->pwd->d_inode);
+	cfid = v9fs_fid_lookup(current->fs->pwd);
+	if (cfid == NULL) {
+		dprintk(DEBUG_ERROR, "process cwd doesn't have a fid\n");
+		return ERR_PTR(-ENOENT);
+	}
+
+	cfidnum = cfid->fid;
+	cde = current->fs->pwd;
+	/* TODO: take advantage of multiwalk */
+
+	fidnum = v9fs_get_idpool(&v9ses->fidpool);
+	if (fidnum < 0) {
+		dprintk(DEBUG_ERROR, "could not get a new fid num\n");
+		err = -ENOENT;
+		goto clunk_fid;
+	}
+
+	while (cde != dentry) {
+		if (cde == cde->d_parent) {
+			dprintk(DEBUG_ERROR, "can't find dentry\n");
+			err = -ENOENT;
+			goto clunk_fid;
+		}
+
+		err = v9fs_t_walk(v9ses, cfidnum, fidnum, "..", NULL);
+		if (err < 0) {
+			dprintk(DEBUG_ERROR, "problem walking to parent\n");
+			goto clunk_fid;
+		}
+
+		cfidnum = fidnum;
+		cde = cde->d_parent;
+	}
+
+	return v9fs_fid_create(dentry, v9ses, fidnum, 0);
+
+clunk_fid:
+	v9fs_t_clunk(v9ses, fidnum, NULL);
+	return ERR_PTR(err);
+}
+
+/**
  * v9fs_fid_lookup - retrieve the right fid from a  particular dentry
  * @dentry: dentry to look for fid in
  * @type: intent of lookup (operation or traversal)
@@ -119,49 +179,25 @@ void v9fs_fid_destroy(struct v9fs_fid *fid)
  *
  */
 
-struct v9fs_fid *v9fs_fid_lookup(struct dentry *dentry, int type)
+struct v9fs_fid *v9fs_fid_lookup(struct dentry *dentry)
 {
 	struct list_head *fid_list = (struct list_head *)dentry->d_fsdata;
 	struct v9fs_fid *current_fid = NULL;
 	struct v9fs_fid *temp = NULL;
 	struct v9fs_fid *return_fid = NULL;
-	int found_parent = 0;
-	int found_user = 0;
 
-	dprintk(DEBUG_9P, " dentry: %s (%p) type %d\n", dentry->d_iname, dentry,
-		type);
+	dprintk(DEBUG_9P, " dentry: %s (%p)\n", dentry->d_iname, dentry);
 
-	if (fid_list && !list_empty(fid_list)) {
+	if (fid_list) {
 		list_for_each_entry_safe(current_fid, temp, fid_list, list) {
-			if (current_fid->uid == current->uid) {
-				if (return_fid == NULL) {
-					if ((type == FID_OP)
-					    || (!current_fid->fidopen)) {
-						return_fid = current_fid;
-						found_user = 1;
-					}
-				}
-			}
-			if (current_fid->pid == current->real_parent->pid) {
-				if ((return_fid == NULL) || (found_parent)
-				    || (found_user)) {
-					if ((type == FID_OP)
-					    || (!current_fid->fidopen)) {
-						return_fid = current_fid;
-						found_parent = 1;
-						found_user = 0;
-					}
-				}
-			}
-			if (current_fid->pid == current->pid) {
-				if ((type == FID_OP) ||
-				    (!current_fid->fidopen)) {
-					return_fid = current_fid;
-					found_parent = 0;
-					found_user = 0;
-				}
+			if (!current_fid->fidcreate) {
+				return_fid = current_fid;
+				break;
 			}
 		}
+
+		if (!return_fid)
+			return_fid = current_fid;
 	}
 
 	/* we are at the root but didn't match */
@@ -187,55 +223,33 @@ struct v9fs_fid *v9fs_fid_lookup(struct dentry *dentry, int type)
 
 /* XXX - there may be some duplication we can get rid of */
 		if (par == dentry) {
-			/* we need to fid_lookup the starting point */
-			int fidnum = -1;
-			int oldfid = -1;
-			int result = -1;
-			struct v9fs_session_info *v9ses =
-			    v9fs_inode2v9ses(current->fs->pwd->d_inode);
-
-			current_fid =
-			    v9fs_fid_lookup(current->fs->pwd, FID_WALK);
-			if (current_fid == NULL) {
-				dprintk(DEBUG_ERROR,
-					"process cwd doesn't have a fid\n");
-				return return_fid;
-			}
-			oldfid = current_fid->fid;
-			par = current->fs->pwd;
-			/* TODO: take advantage of multiwalk */
+			return_fid = v9fs_fid_walk_up(dentry);
+			if (IS_ERR(return_fid))
+				return_fid = NULL;
+		}
+	}
 
-			fidnum = v9fs_get_idpool(&v9ses->fidpool);
-			if (fidnum < 0) {
-				dprintk(DEBUG_ERROR,
-					"could not get a new fid num\n");
-				return return_fid;
-			}
+	return return_fid;
+}
 
-			while (par != dentry) {
-				result =
-				    v9fs_t_walk(v9ses, oldfid, fidnum, "..",
-						NULL);
-				if (result < 0) {
-					dprintk(DEBUG_ERROR,
-						"problem walking to parent\n");
-
-					break;
-				}
-				oldfid = fidnum;
-				if (par == par->d_parent) {
-					dprintk(DEBUG_ERROR,
-						"can't find dentry\n");
-					break;
-				}
-				par = par->d_parent;
-			}
-			if (par == dentry) {
-				return_fid = v9fs_fid_create(dentry);
-				return_fid->fid = fidnum;
+struct v9fs_fid *v9fs_fid_get_created(struct dentry *dentry)
+{
+	struct list_head *fid_list;
+	struct v9fs_fid *fid, *ftmp, *ret;
+
+	dprintk(DEBUG_9P, " dentry: %s (%p)\n", dentry->d_iname, dentry);
+	fid_list = (struct list_head *)dentry->d_fsdata;
+	ret = NULL;
+	if (fid_list) {
+		list_for_each_entry_safe(fid, ftmp, fid_list, list) {
+			if (fid->fidcreate && fid->pid == current->pid) {
+				list_del(&fid->list);
+				ret = fid;
+				break;
 			}
 		}
 	}
 
-	return return_fid;
+	dprintk(DEBUG_9P, "return %p\n", ret);
+	return ret;
 }