rcu: Add full-sized polling for start_poll_expedited()

The start_poll_synchronize_rcu_expedited() 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
start_poll_synchronize_rcu_expedited_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@kernel.org>

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 6bc30e4..653e357 100644 (file)
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -49,6 +49,11 @@ static inline unsigned long start_poll_synchronize_rcu_expedited(void)
        return start_poll_synchronize_rcu();
 }
 
+static inline void start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
+{
+       rgosp->rgos_norm = start_poll_synchronize_rcu_expedited();
+}
+
 static inline void cond_synchronize_rcu_expedited(unsigned long oldstate)
 {
        cond_synchronize_rcu(oldstate);

diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 8f2e0f0..7151fd8 100644 (file)
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -48,6 +48,7 @@ struct rcu_gp_oldstate {
 };
 
 unsigned long start_poll_synchronize_rcu_expedited(void);
+void start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp);
 void cond_synchronize_rcu_expedited(unsigned long oldstate);
 unsigned long get_state_synchronize_rcu(void);
 void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp);

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 68387cc..f9ca335 100644 (file)
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -89,6 +89,7 @@ torture_param(bool, gp_normal, false, "Use normal (non-expedited) GP wait primit
 torture_param(bool, gp_poll, false, "Use polling GP wait primitives");
 torture_param(bool, gp_poll_exp, false, "Use polling expedited GP wait primitives");
 torture_param(bool, gp_poll_full, false, "Use polling full-state GP wait primitives");
+torture_param(bool, gp_poll_exp_full, false, "Use polling full-state expedited GP wait primitives");
 torture_param(bool, gp_sync, false, "Use synchronous GP wait primitives");
 torture_param(int, irqreader, 1, "Allow RCU readers from irq handlers");
 torture_param(int, leakpointer, 0, "Leak pointer dereferences from readers");
@@ -201,12 +202,14 @@ static int rcu_torture_writer_state;
 #define RTWS_POLL_GET          9
 #define RTWS_POLL_GET_FULL     10
 #define RTWS_POLL_GET_EXP      11
-#define RTWS_POLL_WAIT         12
-#define RTWS_POLL_WAIT_FULL    13
-#define RTWS_POLL_WAIT_EXP     14
-#define RTWS_SYNC              15
-#define RTWS_STUTTER           16
-#define RTWS_STOPPING          17
+#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
 static const char * const rcu_torture_writer_state_names[] = {
        "RTWS_FIXED_DELAY",
        "RTWS_DELAY",
@@ -220,9 +223,11 @@ static const char * const rcu_torture_writer_state_names[] = {
        "RTWS_POLL_GET",
        "RTWS_POLL_GET_FULL",
        "RTWS_POLL_GET_EXP",
+       "RTWS_POLL_GET_EXP_FULL",
        "RTWS_POLL_WAIT",
        "RTWS_POLL_WAIT_FULL",
        "RTWS_POLL_WAIT_EXP",
+       "RTWS_POLL_WAIT_EXP_FULL",
        "RTWS_SYNC",
        "RTWS_STUTTER",
        "RTWS_STOPPING",
@@ -337,6 +342,7 @@ struct rcu_torture_ops {
        void (*exp_sync)(void);
        unsigned long (*get_gp_state_exp)(void);
        unsigned long (*start_gp_poll_exp)(void);
+       void (*start_gp_poll_exp_full)(struct rcu_gp_oldstate *rgosp);
        bool (*poll_gp_state_exp)(unsigned long oldstate);
        void (*cond_sync_exp)(unsigned long oldstate);
        unsigned long (*get_gp_state)(void);
@@ -528,6 +534,7 @@ static struct rcu_torture_ops rcu_ops = {
        .cond_sync              = cond_synchronize_rcu,
        .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,
        .poll_gp_state_exp      = poll_state_synchronize_rcu,
        .cond_sync_exp          = cond_synchronize_rcu_expedited,
        .call                   = call_rcu,
@@ -1169,13 +1176,14 @@ 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_normal1 = gp_normal, gp_poll1 = gp_poll;
-       bool gp_poll_full1 = gp_poll_full, gp_sync1 = gp_sync;
+       bool 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 &&
+       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_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 && cur_ops->get_gp_state && cur_ops->cond_sync) {
                synctype[nsynctypes++] = RTWS_COND_GET;
@@ -1219,6 +1227,13 @@ static void rcu_torture_write_types(void)
        } else if (gp_poll_exp && (!cur_ops->start_gp_poll_exp || !cur_ops->poll_gp_state_exp)) {
                pr_alert("%s: gp_poll_exp without primitives.\n", __func__);
        }
+       if (gp_poll_exp_full1 && cur_ops->start_gp_poll_exp_full && cur_ops->poll_gp_state_full) {
+               synctype[nsynctypes++] = RTWS_POLL_GET_EXP_FULL;
+               pr_info("%s: Testing polling full-state expedited GPs.\n", __func__);
+       } else if (gp_poll_exp_full &&
+                  (!cur_ops->start_gp_poll_exp_full || !cur_ops->poll_gp_state_full)) {
+               pr_alert("%s: gp_poll_exp_full without primitives.\n", __func__);
+       }
        if (gp_sync1 && cur_ops->sync) {
                synctype[nsynctypes++] = RTWS_SYNC;
                pr_info("%s: Testing normal GPs.\n", __func__);
@@ -1408,6 +1423,15 @@ rcu_torture_writer(void *arg)
                                                                  &rand);
                                rcu_torture_pipe_update(old_rp);
                                break;
+                       case RTWS_POLL_GET_EXP_FULL:
+                               rcu_torture_writer_state = RTWS_POLL_GET_EXP_FULL;
+                               cur_ops->start_gp_poll_exp_full(&gp_snap_full);
+                               rcu_torture_writer_state = RTWS_POLL_WAIT_EXP_FULL;
+                               while (!cur_ops->poll_gp_state_full(&gp_snap_full))
+                                       torture_hrtimeout_jiffies(torture_random(&rand) % 16,
+                                                                 &rand);
+                               rcu_torture_pipe_update(old_rp);
+                               break;
                        case RTWS_SYNC:
                                rcu_torture_writer_state = RTWS_SYNC;
                                do_rtws_sync(&rand, cur_ops->sync);
@@ -1537,6 +1561,13 @@ rcu_torture_fakewriter(void *arg)
                                                                  &rand);
                                }
                                break;
+                       case RTWS_POLL_GET_EXP_FULL:
+                               cur_ops->start_gp_poll_exp_full(&gp_snap_full);
+                               while (!cur_ops->poll_gp_state_full(&gp_snap_full)) {
+                                       torture_hrtimeout_jiffies(torture_random(&rand) % 16,
+                                                                 &rand);
+                               }
+                               break;
                        case RTWS_SYNC:
                                cur_ops->sync();
                                break;

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index be66758..18128ee 100644 (file)
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -1027,6 +1027,24 @@ unsigned long start_poll_synchronize_rcu_expedited(void)
 }
 EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited);
 
+/**
+ * start_poll_synchronize_rcu_expedited_full - Take a full snapshot and start expedited grace period
+ * @rgosp: Place to put snapshot of grace-period state
+ *
+ * Places the normal and expedited grace-period states in rgosp.  This
+ * state value can be passed to a later call to cond_synchronize_rcu_full()
+ * or poll_state_synchronize_rcu_full() to determine whether or not a
+ * grace period (whether normal or expedited) has elapsed in the meantime.
+ * If the needed expedited grace period is not already slated to start,
+ * initiates that grace period.
+ */
+void start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
+{
+       get_state_synchronize_rcu_full(rgosp);
+       (void)start_poll_synchronize_rcu_expedited();
+}
+EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited_full);
+
 /**
  * cond_synchronize_rcu_expedited - Conditionally wait for an expedited RCU grace period
  *