The cond_synchronize_rcu() API compresses the combined expedited and
normal grace-period states into a single unsigned long, which conserves
storage, but can miss grace periods in certain cases involving overlapping
normal and expedited grace periods. Missing the occasional grace period
is usually not a problem, but there are use cases that care about each
and every grace period.
This commit therefore adds yet another member of the full-state RCU
grace-period polling API, which is the cond_synchronize_rcu_full()
function. This uses up to three times the storage (rcu_gp_oldstate
structure instead of unsigned long), but is guaranteed not to miss
grace periods.
[ paulmck: Apply feedback from kernel test robot and Julia Lawall. ]
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
include/linux/rcutiny.h | 5 +++
include/linux/rcutree.h | 1 +
kernel/rcu/rcutorture.c | 67 +++++++++++++++++++++++++++++------------
kernel/rcu/tree.c | 28 ++++++++++++++++-
4 files changed, 80 insertions(+), 21 deletions(-)
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 653e35777a99b..3bee97f76bf43 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -44,6 +44,11 @@ static inline void cond_synchronize_rcu(unsigned long oldstate)
might_sleep();
}
+static inline void cond_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
+{
+ cond_synchronize_rcu(rgosp->rgos_norm);
+}
+
static inline unsigned long start_poll_synchronize_rcu_expedited(void)
{
return start_poll_synchronize_rcu();
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 7151fd8617365..1b44288c027da 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -57,6 +57,7 @@ void start_poll_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp);
bool poll_state_synchronize_rcu(unsigned long oldstate);
bool poll_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp);
void cond_synchronize_rcu(unsigned long oldstate);
+void cond_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp);
bool rcu_is_idle_cpu(int cpu);
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index f9ca33555debf..9d22161bf7700 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -84,6 +84,7 @@ torture_param(int, fwd_progress_holdoff, 60, "Time between forward-progress test
torture_param(bool, fwd_progress_need_resched, 1, "Hide cond_resched() behind need_resched()");
torture_param(bool, gp_cond, false, "Use conditional/async GP wait primitives");
torture_param(bool, gp_cond_exp, false, "Use conditional/async expedited GP wait primitives");
+torture_param(bool, gp_cond_full, false, "Use conditional/async full-state GP wait primitives");
torture_param(bool, gp_exp, false, "Use expedited GP wait primitives");
torture_param(bool, gp_normal, false, "Use normal (non-expedited) GP wait primitives");
torture_param(bool, gp_poll, false, "Use polling GP wait primitives");
@@ -196,20 +197,22 @@ static int rcu_torture_writer_state;
#define RTWS_DEF_FREE 3
#define RTWS_EXP_SYNC 4
#define RTWS_COND_GET 5
-#define RTWS_COND_GET_EXP 6
-#define RTWS_COND_SYNC 7
-#define RTWS_COND_SYNC_EXP 8
-#define RTWS_POLL_GET 9
-#define RTWS_POLL_GET_FULL 10
-#define RTWS_POLL_GET_EXP 11
-#define RTWS_POLL_GET_EXP_FULL 12
-#define RTWS_POLL_WAIT 13
-#define RTWS_POLL_WAIT_FULL 14
-#define RTWS_POLL_WAIT_EXP 15
-#define RTWS_POLL_WAIT_EXP_FULL 16
-#define RTWS_SYNC 17
-#define RTWS_STUTTER 18
-#define RTWS_STOPPING 19
+#define RTWS_COND_GET_FULL 6
+#define RTWS_COND_GET_EXP 7
+#define RTWS_COND_SYNC 8
+#define RTWS_COND_SYNC_FULL 9
+#define RTWS_COND_SYNC_EXP 10
+#define RTWS_POLL_GET 11
+#define RTWS_POLL_GET_FULL 12
+#define RTWS_POLL_GET_EXP 13
+#define RTWS_POLL_GET_EXP_FULL 14
+#define RTWS_POLL_WAIT 15
+#define RTWS_POLL_WAIT_FULL 16
+#define RTWS_POLL_WAIT_EXP 17
+#define RTWS_POLL_WAIT_EXP_FULL 18
+#define RTWS_SYNC 19
+#define RTWS_STUTTER 20
+#define RTWS_STOPPING 21
static const char * const rcu_torture_writer_state_names[] = {
"RTWS_FIXED_DELAY",
"RTWS_DELAY",
@@ -217,8 +220,10 @@ static const char * const rcu_torture_writer_state_names[] = {
"RTWS_DEF_FREE",
"RTWS_EXP_SYNC",
"RTWS_COND_GET",
+ "RTWS_COND_GET_FULL",
"RTWS_COND_GET_EXP",
"RTWS_COND_SYNC",
+ "RTWS_COND_SYNC_FULL",
"RTWS_COND_SYNC_EXP",
"RTWS_POLL_GET",
"RTWS_POLL_GET_FULL",
@@ -355,6 +360,7 @@ struct rcu_torture_ops {
bool (*poll_gp_state_full)(struct rcu_gp_oldstate *rgosp);
bool (*poll_need_2gp)(bool poll, bool poll_full);
void (*cond_sync)(unsigned long oldstate);
+ void (*cond_sync_full)(struct rcu_gp_oldstate *rgosp);
call_rcu_func_t call;
void (*cb_barrier)(void);
void (*fqs)(void);
@@ -532,6 +538,7 @@ static struct rcu_torture_ops rcu_ops = {
.poll_gp_state_full = poll_state_synchronize_rcu_full,
.poll_need_2gp = rcu_poll_need_2gp,
.cond_sync = cond_synchronize_rcu,
+ .cond_sync_full = cond_synchronize_rcu_full,
.get_gp_state_exp = get_state_synchronize_rcu,
.start_gp_poll_exp = start_poll_synchronize_rcu_expedited,
.start_gp_poll_exp_full = start_poll_synchronize_rcu_expedited_full,
@@ -1175,16 +1182,17 @@ static int nsynctypes;
*/
static void rcu_torture_write_types(void)
{
- bool gp_cond1 = gp_cond, gp_cond_exp1 = gp_cond_exp, gp_exp1 = gp_exp;
- bool gp_poll_exp1 = gp_poll_exp, gp_poll_exp_full1 = gp_poll_exp_full;
+ bool gp_cond1 = gp_cond, gp_cond_exp1 = gp_cond_exp, gp_cond_full1 = gp_cond_full;
+ bool gp_exp1 = gp_exp, gp_poll_exp1 = gp_poll_exp, gp_poll_exp_full1 = gp_poll_exp_full;
bool gp_normal1 = gp_normal, gp_poll1 = gp_poll, gp_poll_full1 = gp_poll_full;
bool gp_sync1 = gp_sync;
/* Initialize synctype[] array. If none set, take default. */
- if (!gp_cond1 && !gp_cond_exp1 && !gp_exp1 && !gp_poll_exp && !gp_poll_exp_full1 &&
- !gp_normal1 && !gp_poll1 && !gp_poll_full1 && !gp_sync1)
- gp_cond1 = gp_cond_exp1 = gp_exp1 = gp_poll_exp1 = gp_poll_exp_full1 =
- gp_normal1 = gp_poll1 = gp_poll_full1 = gp_sync1 = true;
+ if (!gp_cond1 && !gp_cond_exp1 && !gp_cond_full1 && !gp_exp1 && !gp_poll_exp &&
+ !gp_poll_exp_full1 && !gp_normal1 && !gp_poll1 && !gp_poll_full1 && !gp_sync1)
+ gp_cond1 = gp_cond_exp1 = gp_cond_full1 = gp_exp1 = gp_poll_exp1 =
+ gp_poll_exp_full1 = gp_normal1 = gp_poll1 = gp_poll_full1 =
+ gp_sync1 = true;
if (gp_cond1 && cur_ops->get_gp_state && cur_ops->cond_sync) {
synctype[nsynctypes++] = RTWS_COND_GET;
pr_info("%s: Testing conditional GPs.\n", __func__);
@@ -1197,6 +1205,12 @@ static void rcu_torture_write_types(void)
} else if (gp_cond_exp && (!cur_ops->get_gp_state_exp || !cur_ops->cond_sync_exp)) {
pr_alert("%s: gp_cond_exp without primitives.\n", __func__);
}
+ if (gp_cond_full1 && cur_ops->get_gp_state && cur_ops->cond_sync_full) {
+ synctype[nsynctypes++] = RTWS_COND_GET_FULL;
+ pr_info("%s: Testing conditional full-state GPs.\n", __func__);
+ } else if (gp_cond_full && (!cur_ops->get_gp_state || !cur_ops->cond_sync_full)) {
+ pr_alert("%s: gp_cond_full without primitives.\n", __func__);
+ }
if (gp_exp1 && cur_ops->exp_sync) {
synctype[nsynctypes++] = RTWS_EXP_SYNC;
pr_info("%s: Testing expedited GPs.\n", __func__);
@@ -1396,6 +1410,14 @@ rcu_torture_writer(void *arg)
cur_ops->cond_sync_exp(gp_snap);
rcu_torture_pipe_update(old_rp);
break;
+ case RTWS_COND_GET_FULL:
+ rcu_torture_writer_state = RTWS_COND_GET_FULL;
+ cur_ops->get_gp_state_full(&gp_snap_full);
+ torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand);
+ rcu_torture_writer_state = RTWS_COND_SYNC_FULL;
+ cur_ops->cond_sync_full(&gp_snap_full);
+ rcu_torture_pipe_update(old_rp);
+ break;
case RTWS_POLL_GET:
rcu_torture_writer_state = RTWS_POLL_GET;
gp_snap = cur_ops->start_gp_poll();
@@ -1540,6 +1562,11 @@ rcu_torture_fakewriter(void *arg)
torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand);
cur_ops->cond_sync_exp(gp_snap);
break;
+ case RTWS_COND_GET_FULL:
+ cur_ops->get_gp_state_full(&gp_snap_full);
+ torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand);
+ cur_ops->cond_sync_full(&gp_snap_full);
+ break;
case RTWS_POLL_GET:
gp_snap = cur_ops->start_gp_poll();
while (!cur_ops->poll_gp_state(gp_snap)) {
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 0a24ef4d6b823..5c46c0d34ef0d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3749,7 +3749,6 @@ EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu_full);
/**
* cond_synchronize_rcu - Conditionally wait for an RCU grace period
- *
* @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
*
* If a full RCU grace period has elapsed since the earlier call to
@@ -3773,6 +3772,33 @@ void cond_synchronize_rcu(unsigned long oldstate)
}
EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
+/**
+ * cond_synchronize_rcu_full - Conditionally wait for an RCU grace period
+ * @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full()
+ *
+ * If a full RCU grace period has elapsed since the call to
+ * get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(),
+ * or start_poll_synchronize_rcu_expedited_full() from which @rgosp was
+ * obtained, just return. Otherwise, invoke synchronize_rcu() to wait
+ * for a full grace period.
+ *
+ * Yes, this function does not take counter wrap into account.
+ * But counter wrap is harmless. If the counter wraps, we have waited for
+ * more than 2 billion grace periods (and way more on a 64-bit system!),
+ * so waiting for a couple of additional grace periods should be just fine.
+ *
+ * This function provides the same memory-ordering guarantees that
+ * would be provided by a synchronize_rcu() that was invoked at the call
+ * to the function that provided @rgosp and that returned at the end of
+ * this function.
+ */
+void cond_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
+{
+ if (!poll_state_synchronize_rcu_full(rgosp))
+ synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(cond_synchronize_rcu_full);
+
/*
* Check to see if there is any immediate RCU-related work to be done by
* the current CPU, returning 1 if so and zero otherwise. The checks are
--
2.31.1.189.g2e36527f23
