Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762064AbXFTI5F (ORCPT ); Wed, 20 Jun 2007 04:57:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755035AbXFTI4x (ORCPT ); Wed, 20 Jun 2007 04:56:53 -0400 Received: from wa-out-1112.google.com ([209.85.146.183]:2080 "EHLO wa-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751682AbXFTI4w (ORCPT ); Wed, 20 Jun 2007 04:56:52 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=qitxAJFRtztEr6L8EJvBo3XD8wmC1B9F+SeL2zx/Y1GRW7WGT6pN1rrgBaHwHEx82jiE9SnDV9+FxyOuiUTIRTKeoH/JoaJKgjiJzDY7ouoxRcAkw5cs+mM4sizogPn+pMs4lg8XUXDbnFeaDqjX5ANKVaoD/hgsfkwUrmOUIdw= Message-ID: <344eb09a0706200156l2d22ac65o49b893aa29b17291@mail.gmail.com> Date: Wed, 20 Jun 2007 14:26:52 +0530 From: "Bharata B Rao" To: "Jan Blunck" Subject: Re: [RFC PATCH 3/4] Lookup changes to support union mount. Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20070620055050.GB4267@in.ibm.com> <20070620055326.GE4267@in.ibm.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3126 Lines: 76 On 6/20/07, Jan Blunck wrote: > On Wed, 20 Jun 2007 11:23:26 +0530, Bharata B Rao wrote: > > > +/* > > + * Looks for the given @name in dcache by walking through all the layers > > + * of the union stack, starting from the top. > > + * FIXME: If we don't find the dentry in a upper layer, we descend to the > > + * next layer. So there is a chance to miss this dentry in the top layer > > + * if this is the _first_ time lookup of the dentry in this layer. A real > > + * lookup might have fetched a valid dentry in this layer itself, while we > > + * chose to descend to the next lower layer. One solution is not have this > > + * function itself, do the toplevel lookup in dcache and if it fails proceed > > + * to real_lookup_union() directly. > > + */ > > +struct dentry *__d_lookup_union(struct nameidata *nd, struct qstr *name) > > +{ > > + struct dentry *dentry; > > + struct nameidata nd_tmp; > > + struct vfsmount *mnt = mntget(nd->mnt); > > + struct qstr this; > > + int err; > > + > > + nd_tmp.mnt = nd->mnt; > > + nd_tmp.dentry = nd->dentry; > > + > > + this.name = name->name; > > + this.len = name->len; > > + this.hash = name->hash; > > + > > + do { > > + /* d_hash() is a repetition for the top layer. */ > > + if (nd_tmp.dentry->d_op && nd_tmp.dentry->d_op->d_hash) { > > + err = nd_tmp.dentry->d_op->d_hash(nd_tmp.dentry, &this); > > + if (err < 0) > > + goto out; > > + } > > + > > + dentry = __d_lookup(nd_tmp.dentry, &this); > > + if (dentry) { > > + if (dentry->d_inode) { > > + if (nd->mnt != nd_tmp.mnt) { > > + mntput(nd->mnt); > > + nd->mnt = mntget(nd_tmp.mnt); > > + } > > + mntput(mnt); > > + return dentry; > > + } else { > > + dput(dentry); > > + } > > + } > > + } while (next_union_mount(&nd_tmp)); > > +out: > > + mntput(mnt); > > + return NULL; > > +} > > + > > The reference counting for vfsmount is wrong. next_union_mount() should be > something similar to follow_down(). You should grab the reference to the > underlying mount before doing the lookup. Ok ok, you already have a valid > reference in struct union_mount but anyway. The idea is that a reference to the top layer's vfsmount and dentry is taken by the user of the union mount point/directory (eg. lookup, readdir etc) and that should ensure that all the bottom layers are valid until the top level reference is held. Regards, Bharata. -- "Men come and go but mountains remain" -- Ruskin Bond. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/