From a534c8d15b1f1d0f861fc2bb9e0529bd8486ec3f Mon Sep 17 00:00:00 2001 From: "Aneesh Kumar K.V" Date: Wed, 30 Jun 2010 19:18:50 +0530 Subject: 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 Signed-off-by: Venkateswararao Jujjuri Signed-off-by: Eric Van Hensbergen --- fs/9p/fid.c | 114 +++++++++++++++++++++++++++++++++++++++++------------------- 1 file changed, 78 insertions(+), 36 deletions(-) (limited to 'fs/9p/fid.c') 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; } -- cgit