rculfhash: put thread offline before taking mutex (fix G.P. deadlock)

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/rculfhash.c b/rculfhash.c
index 6cc606d9e0dcbea64a7af89327c3874c636caa4c..f95ef5dc083aa4e22618512708beb37cee22e1e3 100644 (file)
--- a/rculfhash.c
+++ b/rculfhash.c
@@ -221,6 +221,13 @@ struct cds_lfht {
        cds_lfht_compare_fct compare_fct;
        unsigned long hash_seed;
        int flags;
+       /*
+        * We need to put the work threads offline (QSBR) when taking this
+        * mutex, because we use synchronize_rcu within this mutex critical
+        * section, which waits on read-side critical sections, and could
+        * therefore cause grace-period deadlock if we hold off RCU G.P.
+        * completion.
+        */
        pthread_mutex_t resize_mutex;   /* resize mutex: add/del mutex */
        unsigned int in_progress_resize, in_progress_destroy;
        void (*cds_lfht_call_rcu)(struct rcu_head *head,
@@ -228,6 +235,8 @@ struct cds_lfht {
        void (*cds_lfht_synchronize_rcu)(void);
        void (*cds_lfht_rcu_read_lock)(void);
        void (*cds_lfht_rcu_read_unlock)(void);
+       void (*cds_lfht_rcu_thread_offline)(void);
+       void (*cds_lfht_rcu_thread_online)(void);
        unsigned long count;            /* global approximate item count */
        struct ht_items_count *percpu_count;    /* per-cpu item count */
 };
@@ -879,6 +888,7 @@ void init_table_link(struct cds_lfht *ht, unsigned long i, unsigned long len)
 {
        unsigned long j;
 
+       ht->cds_lfht_rcu_thread_online();
        ht->cds_lfht_rcu_read_lock();
        for (j = 0; j < len; j++) {
                struct cds_lfht_node *new_node =
@@ -892,6 +902,7 @@ void init_table_link(struct cds_lfht *ht, unsigned long i, unsigned long len)
                        break;
        }
        ht->cds_lfht_rcu_read_unlock();
+       ht->cds_lfht_rcu_thread_offline();
 }
 
 /*
@@ -942,6 +953,7 @@ void remove_table(struct cds_lfht *ht, unsigned long i, unsigned long len)
 {
        unsigned long j;
 
+       ht->cds_lfht_rcu_thread_online();
        ht->cds_lfht_rcu_read_lock();
        for (j = 0; j < len; j++) {
                struct cds_lfht_node *fini_node =
@@ -957,6 +969,7 @@ void remove_table(struct cds_lfht *ht, unsigned long i, unsigned long len)
                        break;
        }
        ht->cds_lfht_rcu_read_unlock();
+       ht->cds_lfht_rcu_thread_offline();
 }
 
 /*
@@ -1006,7 +1019,9 @@ struct cds_lfht *cds_lfht_new(cds_lfht_hash_fct hash_fct,
                                        void (*func)(struct rcu_head *head)),
                        void (*cds_lfht_synchronize_rcu)(void),
                        void (*cds_lfht_rcu_read_lock)(void),
-                       void (*cds_lfht_rcu_read_unlock)(void))
+                       void (*cds_lfht_rcu_read_unlock)(void),
+                       void (*cds_lfht_rcu_thread_offline)(void),
+                       void (*cds_lfht_rcu_thread_online)(void))
 {
        struct cds_lfht *ht;
        unsigned long order;
@@ -1022,14 +1037,18 @@ struct cds_lfht *cds_lfht_new(cds_lfht_hash_fct hash_fct,
        ht->cds_lfht_synchronize_rcu = cds_lfht_synchronize_rcu;
        ht->cds_lfht_rcu_read_lock = cds_lfht_rcu_read_lock;
        ht->cds_lfht_rcu_read_unlock = cds_lfht_rcu_read_unlock;
+       ht->cds_lfht_rcu_thread_offline = cds_lfht_rcu_thread_offline;
+       ht->cds_lfht_rcu_thread_online = cds_lfht_rcu_thread_online;
        ht->percpu_count = alloc_per_cpu_items_count();
        /* this mutex should not nest in read-side C.S. */
        pthread_mutex_init(&ht->resize_mutex, NULL);
        order = get_count_order_ulong(max(init_size, MIN_TABLE_SIZE)) + 1;
        ht->flags = flags;
+       ht->cds_lfht_rcu_thread_offline();
        pthread_mutex_lock(&ht->resize_mutex);
        init_table(ht, 0, order);
        pthread_mutex_unlock(&ht->resize_mutex);
+       ht->cds_lfht_rcu_thread_online();
        return ht;
 }
 
@@ -1314,9 +1333,11 @@ void cds_lfht_resize(struct cds_lfht *ht, unsigned long new_size)
 {
        resize_target_update_count(ht, new_size);
        CMM_STORE_SHARED(ht->t.resize_initiated, 1);
+       ht->cds_lfht_rcu_thread_offline();
        pthread_mutex_lock(&ht->resize_mutex);
        _do_cds_lfht_resize(ht);
        pthread_mutex_unlock(&ht->resize_mutex);
+       ht->cds_lfht_rcu_thread_online();
 }
 
 static
@@ -1326,9 +1347,11 @@ void do_resize_cb(struct rcu_head *head)
                caa_container_of(head, struct rcu_resize_work, head);
        struct cds_lfht *ht = work->ht;
 
+       ht->cds_lfht_rcu_thread_offline();
        pthread_mutex_lock(&ht->resize_mutex);
        _do_cds_lfht_resize(ht);
        pthread_mutex_unlock(&ht->resize_mutex);
+       ht->cds_lfht_rcu_thread_online();
        poison_free(work);
        cmm_smp_mb();   /* finish resize before decrement */
        uatomic_dec(&ht->in_progress_resize);

diff --git a/tests/test_urcu_hash.c b/tests/test_urcu_hash.c
index 959749568d5589022d4bab6a63fea7a924770cc4..d7c2fc2da4098ea37de585590564e403032fadbe 100644 (file)
--- a/tests/test_urcu_hash.c
+++ b/tests/test_urcu_hash.c
@@ -717,7 +717,8 @@ int main(int argc, char **argv)
                        init_hash_size,
                        opt_auto_resize ? CDS_LFHT_AUTO_RESIZE : 0,
                        call_rcu, synchronize_rcu, rcu_read_lock,
-                       rcu_read_unlock);
+                       rcu_read_unlock, rcu_thread_offline,
+                       rcu_thread_online);
        ret = populate_hash();
        assert(!ret);
         err = create_all_cpu_call_rcu_data(0);

diff --git a/urcu/rculfhash.h b/urcu/rculfhash.h
index 8f501ea29b7b1e549c9b2d87f9ecf2e769251af0..4e0b1975a37be667f6a3306b72167ac79aa6efa9 100644 (file)
--- a/urcu/rculfhash.h
+++ b/urcu/rculfhash.h
@@ -94,7 +94,9 @@ struct cds_lfht *cds_lfht_new(cds_lfht_hash_fct hash_fct,
                                void (*func)(struct rcu_head *head)),
                        void (*cds_lfht_synchronize_rcu)(void),
                        void (*cds_lfht_rcu_read_lock)(void),
-                       void (*cds_lfht_rcu_read_unlock)(void));
+                       void (*cds_lfht_rcu_read_unlock)(void),
+                       void (*cds_lfht_rcu_thread_offline)(void),
+                       void (*cds_lfht_rcu_thread_online)(void));
 
 /*
  * cds_lfht_destroy - destroy a hash table.