Return-Path: Received: from fieldses.org ([173.255.197.46]:46894 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751108AbbEDVsY (ORCPT ); Mon, 4 May 2015 17:48:24 -0400 Date: Mon, 4 May 2015 17:48:22 -0400 From: "J. Bruce Fields" To: NeilBrown Cc: Al Viro , Kinglong Mee , "linux-nfs@vger.kernel.org" Subject: Re: [PATCH RFC] NFSD: fix cannot umounting mount points under pseudo root Message-ID: <20150504214822.GA16827@fieldses.org> References: <20150429191934.GA23980@fieldses.org> <20150430075225.21a71056@notabene.brown> <20150430213602.GB9509@fieldses.org> <20150501115326.51f5613a@notabene.brown> <20150501020324.GP889@ZenIV.linux.org.uk> <20150501122333.1476c999@notabene.brown> <20150501022939.GQ889@ZenIV.linux.org.uk> <20150501130826.40721dd0@notabene.brown> <20150501132953.GA2583@fieldses.org> <20150503091653.35169382@notabene.brown> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20150503091653.35169382@notabene.brown> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Sun, May 03, 2015 at 09:16:53AM +1000, NeilBrown wrote: > On Fri, 1 May 2015 09:29:53 -0400 "J. Bruce Fields" > wrote: > > > On Fri, May 01, 2015 at 01:08:26PM +1000, NeilBrown wrote: > > > On Fri, 1 May 2015 03:29:40 +0100 Al Viro wrote: > > > > > > > On Fri, May 01, 2015 at 12:23:33PM +1000, NeilBrown wrote: > > > > > > What kind of consistency warranties do callers expect, BTW? You do realize > > > > > > that between iterate_dir() and callbacks an entry might have been removed > > > > > > and/or replaced? > > > > > > > > > > For READDIR_PLUS, lookup_one_len is called on each name and it requires > > > > > i_mutex, so the code currently holds i_mutex over the whole sequence. > > > > > This is triggering a deadlock. > > > > > > > > Yes, I've seen the context. However, you are _not_ holding it between > > > > actual iterate_dir() and those callbacks, which opens a window when > > > > directory might have been changed. > > > > > > > > Again, what kind of consistency is expected by callers? Are they ready to > > > > cope with "there's no such entry anymore" or "inumber is nothing like > > > > what we'd put in ->ino, since it's no the same object" or "->d_type is > > > > completely unrelated to what we'd found, since the damn thing had been > > > > removed and created from scratch"? > > > > > > Ah, sorry. > > > > > > Yes, the callers are prepared for "there's no such entry anymore". > > > They don't use d_type, so don't care if it might be meaningless. > > > NFSv4 doesn't use ino either, but NFSv3 does and isn't properly cautious > > > about ino changing. > > > > > > In nfs3xdr, we should probably pass 'ino' to encode_entryplus_baggage() and > > > thence to compose_entry_fh() and it should report failure if > > > dchild->d_inode->i_ino doesn't match. > > > > Just to make sure I understand the concern..... So it shouldn't really > > be a problem if readdir and lookup find different objects for the same > > name, the problem is just when we mix attributes from the two objects, > > right? Looks like the v3 code could return an inode number derived from > > the readdir and a filehandle from the lookup, which is a problem. The > > v4 code will get everything from the result of the lookup, which should > > be OK. > > That agrees with my understanding, yes. > > I did wonder for a little while about the possibility of a directory > containing both 'a' and 'b', and NFSv4 doing the readdir and the stat of 'a', > and the a "mv a b" happening before the stat of 'b'. > > Then the readdir response will show both 'a' and 'b' referring to the same > object with a link count of 1. > > I can't quite decide if that is a problem or not. > > > > > > > Simply not returning the extra attributes is perfectly acceptable in NFSv3. > > > > Right, so no big deal anyway.--b. > > Not a big deal, but we should really add a patch like the following ("like" > as in "actually compile tested and documented" which this one isn't). Doesn't seem to break anything. Any second thoughts, or can I add a signed-off-by? --b. commit e11f8acace69 Author: NeilBrown Date: Sun May 3 09:16:53 2015 +1000 nfsd: stop READDIRPLUS returning inconsistent attributes The NFSv3 READDIRPLUS gets some of the returned attributes from the readdir, and some from an inode returned from a new lookup. The two objects could be different thanks to intervening renames. The attributes in READDIRPLUS are optional, so let's just skip them if we notice this case. Signed-off-by: J. Bruce Fields diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c index e4b2b4322553..f6e7cbabac5a 100644 --- a/fs/nfsd/nfs3xdr.c +++ b/fs/nfsd/nfs3xdr.c @@ -805,7 +805,7 @@ encode_entry_baggage(struct nfsd3_readdirres *cd, __be32 *p, const char *name, static __be32 compose_entry_fh(struct nfsd3_readdirres *cd, struct svc_fh *fhp, - const char *name, int namlen) + const char *name, int namlen, u64 ino) { struct svc_export *exp; struct dentry *dparent, *dchild; @@ -830,19 +830,21 @@ compose_entry_fh(struct nfsd3_readdirres *cd, struct svc_fh *fhp, goto out; if (d_really_is_negative(dchild)) goto out; + if (dchild->d_inode->i_ino != ino) + goto out; rv = fh_compose(fhp, exp, dchild, &cd->fh); out: dput(dchild); return rv; } -static __be32 *encode_entryplus_baggage(struct nfsd3_readdirres *cd, __be32 *p, const char *name, int namlen) +static __be32 *encode_entryplus_baggage(struct nfsd3_readdirres *cd, __be32 *p, const char *name, int namlen, u64 ino) { struct svc_fh *fh = &cd->scratch; __be32 err; fh_init(fh, NFS3_FHSIZE); - err = compose_entry_fh(cd, fh, name, namlen); + err = compose_entry_fh(cd, fh, name, namlen, ino); if (err) { *p++ = 0; *p++ = 0; @@ -927,7 +929,7 @@ encode_entry(struct readdir_cd *ccd, const char *name, int namlen, p = encode_entry_baggage(cd, p, name, namlen, ino); if (plus) - p = encode_entryplus_baggage(cd, p, name, namlen); + p = encode_entryplus_baggage(cd, p, name, namlen, ino); num_entry_words = p - cd->buffer; } else if (*(page+1) != NULL) { /* temporarily encode entry into next page, then move back to @@ -941,7 +943,7 @@ encode_entry(struct readdir_cd *ccd, const char *name, int namlen, p1 = encode_entry_baggage(cd, p1, name, namlen, ino); if (plus) - p1 = encode_entryplus_baggage(cd, p1, name, namlen); + p1 = encode_entryplus_baggage(cd, p1, name, namlen, ino); /* determine entry word length and lengths to go in pages */ num_entry_words = p1 - tmp;