srcu: faster gp seq wrap-around

Using a higher value for the initial gp sequence counters allows for
wrapping to occur faster. It can help with surfacing any issues that may
be happening as a result of the wrap around.

Signed-off-by: JP Kobryn <inwardvessel@gmail.com>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 13f6f00aecf9c975aff7ca485fb08bb36676dd86..8d56db70d41739b539f6bef27d7ec00b8f5b656d 100644 (file)
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -34,6 +34,9 @@
 #define ULONG_CMP_GE(a, b)     (ULONG_MAX / 2 >= (a) - (b))
 #define ULONG_CMP_LT(a, b)     (ULONG_MAX / 2 < (a) - (b))
 
+#define RCU_SEQ_CTR_SHIFT    2
+#define RCU_SEQ_STATE_MASK   ((1 << RCU_SEQ_CTR_SHIFT) - 1)
+
 /* Exported common interfaces */
 void call_rcu(struct rcu_head *head, rcu_callback_t func);
 void rcu_barrier_tasks(void);

diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 8f3f72480e78b0d467167c777592e6472e3485e7..ed57598394de37eedeb0b97774f0f617cd3da242 100644 (file)
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -129,10 +129,23 @@ struct srcu_struct {
 #define SRCU_STATE_SCAN1       1
 #define SRCU_STATE_SCAN2       2
 
+/*
+ * Values for initializing gp sequence fields. Higher values allow wrap arounds to
+ * occur earlier.
+ * The second value with state is useful in the case of static initialization of
+ * srcu_usage where srcu_gp_seq_needed is expected to have some state value in its
+ * lower bits (or else it will appear to be already initialized within
+ * the call check_init_srcu_struct()).
+ */
+#define SRCU_GP_SEQ_INITIAL_VAL ((0UL - 100UL) << RCU_SEQ_CTR_SHIFT)
+#define SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE (SRCU_GP_SEQ_INITIAL_VAL - 1)
+
 #define __SRCU_USAGE_INIT(name)                                                                        \
 {                                                                                              \
        .lock = __SPIN_LOCK_UNLOCKED(name.lock),                                                \
-       .srcu_gp_seq_needed = -1UL,                                                             \
+       .srcu_gp_seq = SRCU_GP_SEQ_INITIAL_VAL,                                                 \
+       .srcu_gp_seq_needed = SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE,                               \
+       .srcu_gp_seq_needed_exp = SRCU_GP_SEQ_INITIAL_VAL,                                      \
        .work = __DELAYED_WORK_INITIALIZER(name.work, NULL, 0),                                 \
 }
 

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 38238e595a61a45fd263df234e199c722149968b..2bfed9855d67b4937f0bde03e8ab3347da8e7bce 100644 (file)
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -54,9 +54,6 @@
  *                                     grace-period sequence number.
  */
 
-#define RCU_SEQ_CTR_SHIFT      2
-#define RCU_SEQ_STATE_MASK     ((1 << RCU_SEQ_CTR_SHIFT) - 1)
-
 /* Low-order bit definition for polled grace-period APIs. */
 #define RCU_GET_STATE_COMPLETED        0x1
 

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index b24db425f16d85018bf688dbb5a39249a1b76e91..6fd9c914ce64282c5a864447594a909586350cab 100644 (file)
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -247,7 +247,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
        mutex_init(&ssp->srcu_sup->srcu_cb_mutex);
        mutex_init(&ssp->srcu_sup->srcu_gp_mutex);
        ssp->srcu_idx = 0;
-       ssp->srcu_sup->srcu_gp_seq = 0;
+       ssp->srcu_sup->srcu_gp_seq = SRCU_GP_SEQ_INITIAL_VAL;
        ssp->srcu_sup->srcu_barrier_seq = 0;
        mutex_init(&ssp->srcu_sup->srcu_barrier_mutex);
        atomic_set(&ssp->srcu_sup->srcu_barrier_cpu_cnt, 0);
@@ -258,7 +258,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
        if (!ssp->sda)
                goto err_free_sup;
        init_srcu_struct_data(ssp);
-       ssp->srcu_sup->srcu_gp_seq_needed_exp = 0;
+       ssp->srcu_sup->srcu_gp_seq_needed_exp = SRCU_GP_SEQ_INITIAL_VAL;
        ssp->srcu_sup->srcu_last_gp_end = ktime_get_mono_fast_ns();
        if (READ_ONCE(ssp->srcu_sup->srcu_size_state) == SRCU_SIZE_SMALL && SRCU_SIZING_IS_INIT()) {
                if (!init_srcu_struct_nodes(ssp, GFP_ATOMIC))
@@ -266,7 +266,8 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
                WRITE_ONCE(ssp->srcu_sup->srcu_size_state, SRCU_SIZE_BIG);
        }
        ssp->srcu_sup->srcu_ssp = ssp;
-       smp_store_release(&ssp->srcu_sup->srcu_gp_seq_needed, 0); /* Init done. */
+       smp_store_release(&ssp->srcu_sup->srcu_gp_seq_needed,
+                       SRCU_GP_SEQ_INITIAL_VAL); /* Init done. */
        return 0;
 
 err_free_sda: