From: Benny Halevy Subject: Re: [PATCH 12/14] nfsd4: remove use of mutex for file_hashtable Date: Wed, 11 Mar 2009 20:52:14 +0200 Message-ID: <49B8085E.5080808@panasas.com> References: <1236731222-3294-1-git-send-email-bfields@fieldses.org> <1236731222-3294-2-git-send-email-bfields@fieldses.org> <1236731222-3294-3-git-send-email-bfields@fieldses.org> <1236731222-3294-4-git-send-email-bfields@fieldses.org> <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> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: linux-nfs@vger.kernel.org, "J. Bruce Fields" , Alexandros Batsakis To: "J. Bruce Fields" Return-path: Received: from gw-ca.panasas.com ([209.116.51.66]:20561 "EHLO laguna.int.panasas.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752860AbZCKSwT (ORCPT ); Wed, 11 Mar 2009 14:52:19 -0400 In-Reply-To: <1236731222-3294-13-git-send-email-bfields@fieldses.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: 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) Benny > get_nfs4_file(fp); > return fp; > } > } > + spin_unlock(&recall_lock); > return NULL; > } >