Return-Path: Received: from fieldses.org ([174.143.236.118]:46091 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756290Ab0LHBMl (ORCPT ); Tue, 7 Dec 2010 20:12:41 -0500 Date: Tue, 7 Dec 2010 20:12:39 -0500 From: "J. Bruce Fields" To: Suresh Jayaraman Cc: Neil Brown , "linux-nfs@vger.kernel.org" Subject: Re: [PATCH] nfsd: Fix possible BUG_ON firing in set_change_info Message-ID: <20101208011239.GB30196@fieldses.org> References: <20101202111430.57275603@notabene.brown> <4CF73AC6.4020105@suse.de> Content-Type: text/plain; charset=us-ascii In-Reply-To: <4CF73AC6.4020105@suse.de> Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 On Thu, Dec 02, 2010 at 11:50:54AM +0530, Suresh Jayaraman wrote: > On 12/02/2010 05:44 AM, Neil Brown wrote: > > > > If vfs_getattr in fill_post_wcc returns an error, we don't > > set fh_post_change. > ^^^ Did you mean fh_post_saved? > > > For NFSv4, this can result in set_change_info triggering a BUG_ON. > > i.e. fh_post_saved being zero isn't really a bug. > > > > So: > > - instead of BUGging when fh_post_saved is zero, just clear ->atomic. > > - if vfs_getattr fails in fill_post_wcc, take a copy of i_ctime anyway. > > This will be used i seg_change_info, but not overly trusted. > > - While we are there, remove the pointless 'if' statements in set_change_info. > > There is no harm setting all the values. > > The 'if' statement was introduced when ext4 i_version support was added > via commit c654b8a9. While there is no harm setting all the values, it > may not really be required. If you mean that you interpret the spec as allowing us to return garbage changeattr values in the non-atomic case, no, I don't agree. It's true that a client that tries to use them must be aware of the potential pitfalls, but not true that we therefore have license to return inaccurate post-op attributes. --b. > > >From the spec: > > "For a client to use the change_info4 information > appropriately and correctly, the server must report the pre- and > post-operation change attribute values atomically. When the server > is unable to report the before and after values atomically with > respect to the directory operation, the server must indicate that > fact in the change_info4 return value. When the information is not > atomically reported, the client should not assume that other clients > have not changed the directory." > > Though the spec doesn't talk about the case we have specifically, it > appears to me that the proposed behavior is the best we could aim for. > > > Signed-off-by: NeilBrown > > > > -- > > > > If you think the code is clearer with the if() structure, feel free > > to leave that part unchanged. > > > > NeilBrown > > > > diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c > > index 2a533a0..7e84a85 100644 > > --- a/fs/nfsd/nfs3xdr.c > > +++ b/fs/nfsd/nfs3xdr.c > > @@ -260,9 +260,11 @@ void fill_post_wcc(struct svc_fh *fhp) > > err = vfs_getattr(fhp->fh_export->ex_path.mnt, fhp->fh_dentry, > > &fhp->fh_post_attr); > > fhp->fh_post_change = fhp->fh_dentry->d_inode->i_version; > > - if (err) > > + if (err) { > > fhp->fh_post_saved = 0; > > - else > > + /* Grab the ctime anyway - set_change_info might use it */ > > + fhp->fh_post_attr.ctime = fhp->fh_dentry->d_inode->i_ctime; > > + } else > > fhp->fh_post_saved = 1; > > } > > > > diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h > > index 4d476ff..60fce3d 100644 > > --- a/fs/nfsd/xdr4.h > > +++ b/fs/nfsd/xdr4.h > > @@ -484,18 +484,17 @@ static inline bool nfsd4_not_cached(struct nfsd4_compoundres *resp) > > static inline void > > set_change_info(struct nfsd4_change_info *cinfo, struct svc_fh *fhp) > > { > > - BUG_ON(!fhp->fh_pre_saved || !fhp->fh_post_saved); > > - cinfo->atomic = 1; > > + BUG_ON(!fhp->fh_pre_saved); > > + cinfo->atomic = fhp->fh_post_saved; > > cinfo->change_supported = IS_I_VERSION(fhp->fh_dentry->d_inode); > > - if (cinfo->change_supported) { > > - cinfo->before_change = fhp->fh_pre_change; > > - cinfo->after_change = fhp->fh_post_change; > > - } else { > > - cinfo->before_ctime_sec = fhp->fh_pre_ctime.tv_sec; > > - cinfo->before_ctime_nsec = fhp->fh_pre_ctime.tv_nsec; > > - cinfo->after_ctime_sec = fhp->fh_post_attr.ctime.tv_sec; > > - cinfo->after_ctime_nsec = fhp->fh_post_attr.ctime.tv_nsec; > > - } > > + > > + cinfo->before_change = fhp->fh_pre_change; > > + cinfo->after_change = fhp->fh_post_change; > > + cinfo->before_ctime_sec = fhp->fh_pre_ctime.tv_sec; > > + cinfo->before_ctime_nsec = fhp->fh_pre_ctime.tv_nsec; > > + cinfo->after_ctime_sec = fhp->fh_post_attr.ctime.tv_sec; > > + cinfo->after_ctime_nsec = fhp->fh_post_attr.ctime.tv_nsec; > > + > > } > > > > int nfs4svc_encode_voidres(struct svc_rqst *, __be32 *, void *); > > > -- > Suresh Jayaraman