On Fri, Mar 13, 2009 at 01:18:31PM -0400, bfields wrote:
> On Thu, Mar 12, 2009 at 12:49:25PM +0200, Benny Halevy wrote:
> > On Mar. 12, 2009, 2:05 +0200, "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote:
> > > On Wed, Mar 11, 2009 at 08:52:14PM +0200, Benny Halevy wrote:
> > >>> @@ -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.
>
> Right. So for now I'm taking your first suggestion. Thanks again for
> the review.
By the way, what I've got now is the following.--b.
commit 466c8f95fa8a70335002c2002f7a6c27b65e6e93
Author: J. Bruce Fields <bfields@xxxxxxxxxxxxxx>
Date: Sun Feb 22 14:51:34 2009 -0800
nfsd4: remove use of mutex for file_hashtable
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 <bfields@xxxxxxxxxxxxxx>
Cc: Alexandros Batsakis <batsakis@xxxxxxxxxx>
Reviewed-by: Benny Halevy <bhalevy@xxxxxxxxxxx>
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 fdcd7cf..a4bcfe0 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;
@@ -116,33 +120,23 @@ 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);
- list_del(&fp->fi_hash);
- iput(fp->fi_inode);
- kmem_cache_free(file_slab, fp);
-}
-
static inline void
put_nfs4_file(struct nfs4_file *fi)
{
- kref_put(&fi->fi_ref, free_nfs4_file);
+ if (atomic_dec_and_lock(&fi->fi_ref, &recall_lock)) {
+ list_del(&fi->fi_hash);
+ spin_unlock(&recall_lock);
+ iput(fi->fi_inode);
+ kmem_cache_free(file_slab, fi);
+ }
}
static inline void
get_nfs4_file(struct nfs4_file *fi)
{
- kref_get(&fi->fi_ref);
+ atomic_inc(&fi->fi_ref);
}
static int num_delegations;
@@ -1000,11 +994,13 @@ alloc_init_file(struct inode *ino)
fp = kmem_cache_alloc(file_slab, GFP_KERNEL);
if (fp) {
- kref_init(&fp->fi_ref);
+ atomic_set(&fp->fi_ref, 1);
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 +1173,15 @@ 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) {
get_nfs4_file(fp);
+ spin_unlock(&recall_lock);
return fp;
}
}
+ spin_unlock(&recall_lock);
return NULL;
}
diff --git a/include/linux/nfsd/state.h b/include/linux/nfsd/state.h
index 503b6bb..a6e4a00 100644
--- a/include/linux/nfsd/state.h
+++ b/include/linux/nfsd/state.h
@@ -214,7 +214,7 @@ struct nfs4_stateowner {
* share_acces, share_deny on the file.
*/
struct nfs4_file {
- struct kref fi_ref;
+ atomic_t fi_ref;
struct list_head fi_hash; /* hash by "struct inode *" */
struct list_head fi_stateids;
struct list_head fi_delegations;
--
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