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global resources: > the filecache and the v4 state table > 2/ it prevents races for per-netns config, typically > ensure config changes are synchronised w.r.t. server > startup/shutdown. > > This patch splits out the first used. A subsequent patch improves the > second. > > "nfsd_users" is changed to a kref which is can be taken to delay > the shutdown of global services. nfsd_startup_get(), it is succeeds, > ensure the global services will remain until nfsd_startup_put(). > > The new mutex, nfsd_startup_mutex, is only take for startup and > shutdown. It is not needed to protect the kref. > > The locking needed by nfsd_file_cache_purge() is now provided internally > by that function so calls don't need to be concerned. > > This replaces NFSD_FILE_CACHE_UP which is effective just a flag which > says nfsd_users is non-zero. > > Signed-off-by: NeilBrown > --- > fs/nfsd/export.c | 6 ------ > fs/nfsd/filecache.c | 31 +++++++++++-------------------- > fs/nfsd/nfsd.h | 3 +++ > fs/nfsd/nfssvc.c | 41 +++++++++++++++++++++++++++-------------- > 4 files changed, 41 insertions(+), 40 deletions(-) > > diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c > index cadfc2bae60e..1ea3d72ef5c9 100644 > --- a/fs/nfsd/export.c > +++ b/fs/nfsd/export.c > @@ -243,13 +243,7 @@ static struct cache_head *expkey_alloc(void) > > static void expkey_flush(void) > { > - /* > - * Take the nfsd_mutex here to ensure that the file cache is not > - * destroyed while we're in the middle of flushing. > - */ > - mutex_lock(&nfsd_mutex); > nfsd_file_cache_purge(current->nsproxy->net_ns); > - mutex_unlock(&nfsd_mutex); > } > > static const struct cache_detail svc_expkey_cache_template = { > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > index e108b6c705b4..0a9116b7530c 100644 > --- a/fs/nfsd/filecache.c > +++ b/fs/nfsd/filecache.c > @@ -50,8 +50,6 @@ > > #define NFSD_LAUNDRETTE_DELAY (2 * HZ) > > -#define NFSD_FILE_CACHE_UP (0) > - > /* We only care about NFSD_MAY_READ/WRITE for this cache */ > #define NFSD_FILE_MAY_MASK (NFSD_MAY_READ|NFSD_MAY_WRITE|NFSD_MAY_LOCALIO) > > @@ -70,7 +68,6 @@ struct nfsd_fcache_disposal { > static struct kmem_cache *nfsd_file_slab; > static struct kmem_cache *nfsd_file_mark_slab; > static struct list_lru nfsd_file_lru; > -static unsigned long nfsd_file_flags; > static struct fsnotify_group *nfsd_file_fsnotify_group; > static struct delayed_work nfsd_filecache_laundrette; > static struct rhltable nfsd_file_rhltable > @@ -112,9 +109,12 @@ static const struct rhashtable_params nfsd_file_rhash_params = { > static void > nfsd_file_schedule_laundrette(void) > { > - if (test_bit(NFSD_FILE_CACHE_UP, &nfsd_file_flags)) > - queue_delayed_work(system_unbound_wq, &nfsd_filecache_laundrette, > + if (nfsd_startup_get()) { > + queue_delayed_work(system_unbound_wq, > + &nfsd_filecache_laundrette, > NFSD_LAUNDRETTE_DELAY); > + nfsd_startup_put(); > + } > } > > static void > @@ -795,10 +795,6 @@ nfsd_file_cache_init(void) > { > int ret; > > - lockdep_assert_held(&nfsd_mutex); > - if (test_and_set_bit(NFSD_FILE_CACHE_UP, &nfsd_file_flags) == 1) > - return 0; > - > ret = rhltable_init(&nfsd_file_rhltable, &nfsd_file_rhash_params); > if (ret) > goto out; > @@ -853,8 +849,6 @@ nfsd_file_cache_init(void) > > INIT_DELAYED_WORK(&nfsd_filecache_laundrette, nfsd_file_gc_worker); > out: > - if (ret) > - clear_bit(NFSD_FILE_CACHE_UP, &nfsd_file_flags); > return ret; > out_notifier: > lease_unregister_notifier(&nfsd_file_lease_notifier); > @@ -958,9 +952,10 @@ nfsd_file_cache_start_net(struct net *net) > void > nfsd_file_cache_purge(struct net *net) > { > - lockdep_assert_held(&nfsd_mutex); > - if (test_bit(NFSD_FILE_CACHE_UP, &nfsd_file_flags) == 1) > + if (nfsd_startup_get()) { > __nfsd_file_cache_purge(net); > + nfsd_startup_put(); > + } > } > > void > @@ -975,10 +970,6 @@ nfsd_file_cache_shutdown(void) > { > int i; > > - lockdep_assert_held(&nfsd_mutex); > - if (test_and_clear_bit(NFSD_FILE_CACHE_UP, &nfsd_file_flags) == 0) > - return; > - > lease_unregister_notifier(&nfsd_file_lease_notifier); > shrinker_free(nfsd_file_shrinker); > /* > @@ -1347,8 +1338,7 @@ int nfsd_file_cache_stats_show(struct seq_file *m, void *v) > unsigned long lru = 0, total_age = 0; > > /* Serialize with server shutdown */ > - mutex_lock(&nfsd_mutex); > - if (test_bit(NFSD_FILE_CACHE_UP, &nfsd_file_flags) == 1) { > + if (nfsd_startup_get()) { > struct bucket_table *tbl; > struct rhashtable *ht; > > @@ -1360,8 +1350,9 @@ int nfsd_file_cache_stats_show(struct seq_file *m, void *v) > tbl = rht_dereference_rcu(ht->tbl, ht); > buckets = tbl->size; > rcu_read_unlock(); > + > + nfsd_startup_put(); > } > - mutex_unlock(&nfsd_mutex); > > for_each_possible_cpu(i) { > hits += per_cpu(nfsd_file_cache_hits, i); > diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h > index 1bfd0b4e9af7..8ad9fcc23789 100644 > --- a/fs/nfsd/nfsd.h > +++ b/fs/nfsd/nfsd.h > @@ -80,6 +80,9 @@ extern const struct svc_version nfsd_version2, nfsd_version3, nfsd_version4; > extern struct mutex nfsd_mutex; > extern atomic_t nfsd_th_cnt; /* number of available threads */ > > +bool nfsd_startup_get(void); > +void nfsd_startup_put(void); > + > extern const struct seq_operations nfs_exports_op; > > /* > diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c > index 82b0111ac469..b2080e5a71e6 100644 > --- a/fs/nfsd/nfssvc.c > +++ b/fs/nfsd/nfssvc.c > @@ -270,38 +270,51 @@ static int nfsd_init_socks(struct net *net, const struct cred *cred) > return 0; > } > > -static int nfsd_users = 0; > +static struct kref nfsd_users = KREF_INIT(0); > +static DEFINE_MUTEX(nfsd_startup_mutex); > > static int nfsd_startup_generic(void) > { > - int ret; > + int ret = 0; > > - if (nfsd_users++) > + if (kref_get_unless_zero(&nfsd_users)) > return 0; > + mutex_lock(&nfsd_startup_mutex); > + if (kref_get_unless_zero(&nfsd_users)) > + goto out_unlock; > > ret = nfsd_file_cache_init(); > if (ret) > - goto dec_users; > + goto out_unlock; > > ret = nfs4_state_start(); > if (ret) > goto out_file_cache; > - return 0; > + kref_init(&nfsd_users); > +out_unlock: > + mutex_unlock(&nfsd_startup_mutex); > + return ret; > > out_file_cache: > nfsd_file_cache_shutdown(); > -dec_users: > - nfsd_users--; > - return ret; > + goto out_unlock; > } > > -static void nfsd_shutdown_generic(void) > +static void nfsd_shutdown_cb(struct kref *kref) > { > - if (--nfsd_users) > - return; > - > nfs4_state_shutdown(); > nfsd_file_cache_shutdown(); > + mutex_unlock(&nfsd_startup_mutex); > +} > + > +bool nfsd_startup_get(void) > +{ > + return kref_get_unless_zero(&nfsd_users); > +} > + > +void nfsd_startup_put(void) > +{ > + kref_put_mutex(&nfsd_users, nfsd_shutdown_cb, &nfsd_startup_mutex); > } > > static bool nfsd_needs_lockd(struct nfsd_net *nn) > @@ -416,7 +429,7 @@ static int nfsd_startup_net(struct net *net, const struct cred *cred) > nn->lockd_up = false; > } > out_socks: > - nfsd_shutdown_generic(); > + nfsd_startup_put(); > return ret; > } > > @@ -443,7 +456,7 @@ static void nfsd_shutdown_net(struct net *net) > percpu_ref_exit(&nn->nfsd_net_ref); > > nn->nfsd_net_up = false; > - nfsd_shutdown_generic(); > + nfsd_startup_put(); > } > > static DEFINE_SPINLOCK(nfsd_notifier_lock); [ Adding Cc: chenxiaosong@chenxiaosong.com who seems to be working on a crasher related to nfsd_users. ] I like where this is going. - I'm struggling a little with the names of nfsd_startup_get/put. But I don't have a better suggestion. I think we're marking a critical section of sorts. pin/unpin maybe? - Maybe someone has a way to exercise NFSD service startup and shutdown. We don't have much testing in this area, upstream. A CI-style "do this thing 1000 times while the server is under load" might be good. -- Chuck Lever