Return-Path: linux-nfs-owner@vger.kernel.org Received: from mx1.redhat.com ([209.132.183.28]:43750 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755594Ab3HASpv (ORCPT ); Thu, 1 Aug 2013 14:45:51 -0400 Message-ID: <51FAACD9.8020205@redhat.com> Date: Thu, 01 Aug 2013 14:45:45 -0400 From: Ric Wheeler MIME-Version: 1.0 To: Miklos Szeredi , Trond Myklebust CC: Anand Avati , Brian Foster , Linux FS Devel , Alexander Viro , David Howells , Eric Paris , Linux NFS list Subject: Re: [PATCH] [REPOST] fuse: drop dentry on failed revalidate References: <20130725055209.GA15621@sh-el5.eng.rdu2.redhat.com> <51F13948.3050100@redhat.com> <51F81465.9010402@redhat.com> <20130801163940.GA1356@tucsk.piliscsaba.szeredi.hu> In-Reply-To: <20130801163940.GA1356@tucsk.piliscsaba.szeredi.hu> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Sender: linux-nfs-owner@vger.kernel.org List-ID: On 08/01/2013 12:39 PM, Miklos Szeredi wrote: > On Tue, Jul 30, 2013 at 03:30:45PM -0400, Ric Wheeler wrote: >> On 07/30/2013 12:16 PM, Miklos Szeredi wrote: >>>>> fs/fuse/dir.c | 4 ++++ >>>>> 1 file changed, 4 insertions(+) >>>>> >>>>> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c >>>>> index a1d9047..83c217e 100644 >>>>> --- a/fs/fuse/dir.c >>>>> +++ b/fs/fuse/dir.c >>>>> @@ -226,6 +226,10 @@ static int fuse_dentry_revalidate(struct dentry >>>>> *entry, unsigned int flags) >>>>> if (!err) { >>>>> struct fuse_inode *fi = get_fuse_inode(inode); >>>>> if (outarg.nodeid != get_node_id(inode)) { >>>>> + if (!have_submounts(entry)) { >>>>> + shrink_dcache_parent(entry); >>>>> + d_drop(entry); >>>>> + } >>> Doing d_drop() on a subtree really has problems. Take this example: >>> >>> cd /mnt/foo/bar >>> mkdir my-mount-point >>> [->d_revalidate() drops "/mnt/foo"] >>> mount whatever on ./my-mount-point >>> cd / >>> >>> At this point that mount is not accessible in any way. The only way >>> to umount it is to lazy umount the parent mount. If the parent mount >>> was root, then that's not a practical thing to do. >>> >>> AFAICS nothing prevents this from happening on NFS and root privs are >>> not required (e.g. mounting a fuse fs on an NFS home dir). >>> > Here's a patch that tries to address the mount issue in NFS (and in FUSE in the > future). I haven't yet tested it, just interested in whether the concept looks > OK or not. > > Not sure if the ENOENT is the best error. Also I have a little fear that this > will cause a regression in some weird setup. Possibly we should use a new > dentry flag for unhashing the directory dentry specifically to invalidate it. > > Thanks, > Miklos Adding in the NFS list for broader review. I thought that the issue was primarily in FUSE itself, not seen in practice in NFS? Ric > > > > diff --git a/fs/dcache.c b/fs/dcache.c > index 87bdb53..5c51217 100644 > --- a/fs/dcache.c > +++ b/fs/dcache.c > @@ -1103,6 +1103,34 @@ rename_retry: > } > EXPORT_SYMBOL(have_submounts); > > +static bool __has_unlinked_ancestor(struct dentry *dentry) > +{ > + struct dentry *this; > + > + for (this = dentry; !IS_ROOT(this); this = this->d_parent) { > + if (d_unhashed(this)) > + return true; > + } > + return false; > +} > + > +/* > + * Called by mount code to check if the mountpoint is reachable (e.g. NFS can > + * unhash a directory dentry and then the complete subtree can become > + * unreachable). > + */ > +bool has_unlinked_ancestor(struct dentry *dentry) > +{ > + bool found; > + > + /* Need exclusion wrt. have_submounts() */ > + write_seqlock(&rename_lock); > + found = __has_unlinked_ancestor(dentry); > + write_sequnlock(&rename_lock); > + > + return found; > +} > + > /* > * Search the dentry child list of the specified parent, > * and move any unused dentries to the end of the unused > diff --git a/fs/internal.h b/fs/internal.h > index 7c5f01c..d232355 100644 > --- a/fs/internal.h > +++ b/fs/internal.h > @@ -126,6 +126,7 @@ extern int invalidate_inodes(struct super_block *, bool); > * dcache.c > */ > extern struct dentry *__d_alloc(struct super_block *, const struct qstr *); > +extern bool has_unlinked_ancestor(struct dentry *dentry); > > /* > * read_write.c > diff --git a/fs/namespace.c b/fs/namespace.c > index 7b1ca9b..bb92a9c 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -634,6 +634,15 @@ static struct mountpoint *new_mountpoint(struct dentry *dentry) > } > dentry->d_flags |= DCACHE_MOUNTED; > spin_unlock(&dentry->d_lock); > + > + if (has_unlinked_ancestor(dentry)) { > + spin_lock(&dentry->d_lock); > + dentry->d_flags &= ~DCACHE_MOUNTED; > + spin_unlock(&dentry->d_lock); > + kfree(mp); > + return ERR_PTR(-ENOENT); > + } > + > mp->m_dentry = dentry; > mp->m_count = 1; > list_add(&mp->m_hash, chain);