From: Benny Halevy Subject: Re: [PATCH 12/14] nfsd4: remove use of mutex for file_hashtable Date: Thu, 12 Mar 2009 12:49:25 +0200 Message-ID: <49B8E8B5.4010205@panasas.com> 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> <20090312000540.GB21854@fieldses.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-nfs@vger.kernel.org, Alexandros Batsakis To: "J. Bruce Fields" Return-path: Received: from gw-ca.panasas.com ([209.116.51.66]:30536 "EHLO laguna.int.panasas.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755666AbZCLKta (ORCPT ); Thu, 12 Mar 2009 06:49:30 -0400 In-Reply-To: <20090312000540.GB21854@fieldses.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Mar. 12, 2009, 2:05 +0200, "J. Bruce Fields" wrote: > 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. I see. What matters is the stateids associated with the file. Benny > > 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.