From: "J. Bruce Fields" Subject: Re: [PATCH 12/14] nfsd4: remove use of mutex for file_hashtable Date: Wed, 11 Mar 2009 20:05:40 -0400 Message-ID: <20090312000540.GB21854@fieldses.org> References: <1236731222-3294-5-git-send-email-bfields@fieldses.org> <1236731222-3294-6-git-send-email-bfields@fieldses.org> <1236731222-3294-7-git-send-email-bfields@fieldses.org> <1236731222-3294-8-git-send-email-bfields@fieldses.org> <1236731222-3294-9-git-send-email-bfields@fieldses.org> <1236731222-3294-10-git-send-email-bfields@fieldses.org> <1236731222-3294-11-git-send-email-bfields@fieldses.org> <1236731222-3294-12-git-send-email-bfields@fieldses.org> <1236731222-3294-13-git-send-email-bfields@fieldses.org> <49B8085E.5080808@panasas.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-nfs@vger.kernel.org, Alexandros Batsakis To: Benny Halevy Return-path: Received: from mail.fieldses.org ([141.211.133.115]:58993 "EHLO pickle.fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752604AbZCLAFm (ORCPT ); Wed, 11 Mar 2009 20:05:42 -0400 In-Reply-To: <49B8085E.5080808@panasas.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, Mar 11, 2009 at 08:52:14PM +0200, Benny Halevy wrote: > On Mar. 11, 2009, 2:27 +0200, "J. Bruce Fields" wrote: > > From: J. Bruce Fields > > > > As part of reducing the scope of the client_mutex, and in order to > > remove the need for mutexes from the callback code (so that callbacks > > can be done as asynchronous rpc calls), move manipulations of the > > file_hashtable under the recall_lock. > > > > Update the relevant comments while we're here. > > > > Signed-off-by: J. Bruce Fields > > Cc: Alexandros Batsakis > > --- > > fs/nfsd/nfs4callback.c | 2 -- > > fs/nfsd/nfs4state.c | 29 +++++++++++++++++------------ > > 2 files changed, 17 insertions(+), 14 deletions(-) > > > > diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c > > index 3fd7136..5dcd38e 100644 > > --- a/fs/nfsd/nfs4callback.c > > +++ b/fs/nfsd/nfs4callback.c > > @@ -491,8 +491,6 @@ out_put_cred: > > * or deleg_return. > > */ > > put_nfs4_client(clp); > > - nfs4_lock_state(); > > nfs4_put_delegation(dp); > > - nfs4_unlock_state(); > > return; > > } > > diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c > > index 56e81f9..2f4cb9a 100644 > > --- a/fs/nfsd/nfs4state.c > > +++ b/fs/nfsd/nfs4state.c > > @@ -78,14 +78,18 @@ static struct nfs4_delegation * find_delegation_stateid(struct inode *ino, state > > static char user_recovery_dirname[PATH_MAX] = "/var/lib/nfs/v4recovery"; > > static void nfs4_set_recdir(char *recdir); > > > > -/* Locking: > > - * > > - * client_mutex: > > - * protects clientid_hashtbl[], clientstr_hashtbl[], > > - * unconfstr_hashtbl[], uncofid_hashtbl[]. > > - */ > > +/* Locking: */ > > + > > +/* Currently used for almost all code touching nfsv4 state: */ > > static DEFINE_MUTEX(client_mutex); > > > > +/* > > + * Currently used for the del_recall_lru and file hash table. In an > > + * effort to decrease the scope of the client_mutex, this spinlock may > > + * eventually cover more: > > + */ > > +static DEFINE_SPINLOCK(recall_lock); > > + > > static struct kmem_cache *stateowner_slab = NULL; > > static struct kmem_cache *file_slab = NULL; > > static struct kmem_cache *stateid_slab = NULL; > > @@ -116,19 +120,15 @@ opaque_hashval(const void *ptr, int nbytes) > > return x; > > } > > > > -/* > > - * Delegation state > > - */ > > - > > -/* recall_lock protects the del_recall_lru */ > > -static DEFINE_SPINLOCK(recall_lock); > > static struct list_head del_recall_lru; > > > > static void > > free_nfs4_file(struct kref *kref) > > { > > struct nfs4_file *fp = container_of(kref, struct nfs4_file, fi_ref); > > + spin_lock(&recall_lock); > > list_del(&fp->fi_hash); > > + spin_unlock(&recall_lock); > > iput(fp->fi_inode); > > kmem_cache_free(file_slab, fp); > > } > > @@ -1004,7 +1004,9 @@ alloc_init_file(struct inode *ino) > > INIT_LIST_HEAD(&fp->fi_hash); > > INIT_LIST_HEAD(&fp->fi_stateids); > > INIT_LIST_HEAD(&fp->fi_delegations); > > + spin_lock(&recall_lock); > > list_add(&fp->fi_hash, &file_hashtbl[hashval]); > > + spin_unlock(&recall_lock); > > fp->fi_inode = igrab(ino); > > fp->fi_id = current_fileid++; > > fp->fi_had_conflict = false; > > @@ -1177,12 +1179,15 @@ find_file(struct inode *ino) > > unsigned int hashval = file_hashval(ino); > > struct nfs4_file *fp; > > > > + spin_lock(&recall_lock); > > list_for_each_entry(fp, &file_hashtbl[hashval], fi_hash) { > > if (fp->fi_inode == ino) { > > + spin_unlock(&recall_lock); > > Hmm, I'm afraid there's a race here since potentially > you could take the reference on the file after it has been freed. > find_file should call get_nfs4_file if and only if it's still hashed, > i.e. atomically with looking it up on the list. > > On the same lines, the lock should be taken in put_nfs4_file > rather than in free_nfs4_file. > > That being said, I'm not sure we're unhashing the file in the right > place... it's too late for me right now but my hunch is that open > should alloc_init the nfs4_file as done today and close should unhash > it (under the recall spinlock), and then put it. > put_nfs4_file can stay the same and free_nfs4_file should just do the > iput and kmem_cache_free. > > The main difference is that find_file will fail finding the nfs4_file > struct after close. (get_nfs4_file in find_file should still happen > under the lock though) It's probably better for the nfs4_file to be visible longer, but either is correct. The only reason the delegation has a reference on this is to keep track of which files have seen conflicts. Maybe there's some better way. Thanks for catching this.... --b.