[PATCH tip/core/rcu 0/19] Miscellaneous fixes for v5.8

[PATCH tip/core/rcu 0/19] Miscellaneous fixes for v5.8

[Paul E. McKenney]

Hello!

This series provides miscellaneous fixes.

1.	Add KCSAN stubs to tree.c.

2.	Add KCSAN stubs to srcutree.c.

3.	Mark rcu_state.ncpus to detect concurrent writes.

4.	Add *_ONCE() and data_race() to rcu_node ->exp_tasks and also
	add some needed locking.

5.	Add READ_ONCE and data_race() to rcu_node ->boost_tasks.

6.	Add data_race() to ->srcu_lock_count and ->srcu_unlock_count arrays.

7.	Add WRITE_ONCE() to rcu_node ->boost_tasks.

8.	Use data_race() for RCU CPU stall-warning prints.

9.	Make drm_dp_mst_dsc_aux_for_port() safe for old compilers.
	Hey, I have the hair color for it!!!  ;-)

10.	Expedite first two FQS scans under callback-overload conditions.

11.	Fix the (t=0 jiffies) false positive, courtesy of Zhaolong Zhang.

12.	Revert "rculist: Describe variadic macro argument in a
	Sphinx-compatible way" due to Sphinx now being able to handle
	the original description, courtesy of Jonathan Neuschäfer.

13.	Get rid of some doc warnings in update.c, courtesy of
	Mauro Carvalho Chehab.

14.	Mark rcu_state.gp_seq to detect more concurrent writes.

15.	Replace assigned pointer ret value by corresponding boolean value,
	courtesy of Jules Irenge.

16.	Replace 1 by true in use_softirq initialization, courtesy of
	Jules Irenge.

17.	Convert ULONG_CMP_GE() to time_after() for jiffy comparison.

18.	Convert rcu_initiate_boost() ULONG_CMP_GE() to time_after().

19.	Convert rcu_nohz_full_cpu() ULONG_CMP_LT() to time_before().

							Thanx, Paul

------------------------------------------------------------------------

 drivers/gpu/drm/drm_dp_mst_topology.c |    2 -
 include/linux/rculist.h               |    4 +--
 kernel/rcu/srcutree.c                 |   21 ++++++++++++++---
 kernel/rcu/tree.c                     |   41 ++++++++++++++++++++++++++++------
 kernel/rcu/tree.h                     |    1 
 kernel/rcu/tree_exp.h                 |   19 +++++++++------
 kernel/rcu/tree_plugin.h              |   21 +++++++++--------
 kernel/rcu/tree_stall.h               |   38 +++++++++++++++----------------
 kernel/rcu/update.c                   |   14 +++++------
 9 files changed, 103 insertions(+), 58 deletions(-)

[PATCH tip/core/rcu 01/19] rcu: Add KCSAN stubs

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

This commit adds stubs for KCSAN's data_race(), ASSERT_EXCLUSIVE_WRITER(),
and ASSERT_EXCLUSIVE_ACCESS() macros to allow code using these macros to
move ahead.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 06548e2..f13130a 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -67,6 +67,19 @@
 #endif
 #define MODULE_PARAM_PREFIX "rcutree."
 
+#ifndef data_race
+#define data_race(expr)							\
+	({								\
+		expr;							\
+	})
+#endif
+#ifndef ASSERT_EXCLUSIVE_WRITER
+#define ASSERT_EXCLUSIVE_WRITER(var) do { } while (0)
+#endif
+#ifndef ASSERT_EXCLUSIVE_ACCESS
+#define ASSERT_EXCLUSIVE_ACCESS(var) do { } while (0)
+#endif
+
 /* Data structures. */
 
 /*
-- 
2.9.5

[PATCH tip/core/rcu 02/19] srcu: Add KCSAN stubs

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

This commit adds stubs for KCSAN's data_race(), ASSERT_EXCLUSIVE_WRITER(),
and ASSERT_EXCLUSIVE_ACCESS() macros to allow code using these macros to
move ahead.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/srcutree.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 0c71505..ba2b751 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -29,6 +29,19 @@
 #include "rcu.h"
 #include "rcu_segcblist.h"
 
+#ifndef data_race
+#define data_race(expr)							\
+	({								\
+		expr;							\
+	})
+#endif
+#ifndef ASSERT_EXCLUSIVE_WRITER
+#define ASSERT_EXCLUSIVE_WRITER(var) do { } while (0)
+#endif
+#ifndef ASSERT_EXCLUSIVE_ACCESS
+#define ASSERT_EXCLUSIVE_ACCESS(var) do { } while (0)
+#endif
+
 /* Holdoff in nanoseconds for auto-expediting. */
 #define DEFAULT_SRCU_EXP_HOLDOFF (25 * 1000)
 static ulong exp_holdoff = DEFAULT_SRCU_EXP_HOLDOFF;
-- 
2.9.5

[PATCH tip/core/rcu 03/19] rcu: Mark rcu_state.ncpus to detect concurrent writes

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

The rcu_state structure's ncpus field is only to be modified by the
CPU-hotplug CPU-online code path, which is single-threaded.  This
commit therefore enlists KCSAN's help in enforcing this restriction.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f13130a..4fd3e0f 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3612,6 +3612,7 @@ void rcu_cpu_starting(unsigned int cpu)
 	nbits = bitmap_weight(&oldmask, BITS_PER_LONG);
 	/* Allow lockless access for expedited grace periods. */
 	smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + nbits); /* ^^^ */
+	ASSERT_EXCLUSIVE_WRITER(rcu_state.ncpus);
 	rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
 	rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
 	rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags);
-- 
2.9.5

[PATCH tip/core/rcu 04/19] rcu: Add *_ONCE() and data_race() to rcu_node ->exp_tasks plus locking

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

There are lockless loads from the rcu_node structure's ->exp_tasks field,
so this commit causes all stores to use WRITE_ONCE() and all lockless
loads to use READ_ONCE() or data_race(), with the latter for debug
prints.  This code also did a unprotected traversal of the linked list
pointed into by ->exp_tasks, so this commit also acquires the rcu_node
structure's ->lock to properly protect this traversal.  This list was
traversed unprotected only when printing an RCU CPU stall warning for
an expedited grace period, so the odds of seeing this in production are
not all that high.

This data race was reported by KCSAN.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree_exp.h    | 19 +++++++++++--------
 kernel/rcu/tree_plugin.h |  8 ++++----
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 1a617b9..c2b04da 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -150,7 +150,7 @@ static void __maybe_unused sync_exp_reset_tree(void)
 static bool sync_rcu_exp_done(struct rcu_node *rnp)
 {
 	raw_lockdep_assert_held_rcu_node(rnp);
-	return rnp->exp_tasks == NULL &&
+	return READ_ONCE(rnp->exp_tasks) == NULL &&
 	       READ_ONCE(rnp->expmask) == 0;
 }
 
@@ -373,7 +373,7 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
 	 * until such time as the ->expmask bits are cleared.
 	 */
 	if (rcu_preempt_has_tasks(rnp))
-		rnp->exp_tasks = rnp->blkd_tasks.next;
+		WRITE_ONCE(rnp->exp_tasks, rnp->blkd_tasks.next);
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 
 	/* IPI the remaining CPUs for expedited quiescent state. */
@@ -542,8 +542,8 @@ static void synchronize_rcu_expedited_wait(void)
 		}
 		pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
 			jiffies - jiffies_start, rcu_state.expedited_sequence,
-			READ_ONCE(rnp_root->expmask),
-			".T"[!!rnp_root->exp_tasks]);
+			data_race(rnp_root->expmask),
+			".T"[!!data_race(rnp_root->exp_tasks)]);
 		if (ndetected) {
 			pr_err("blocking rcu_node structures:");
 			rcu_for_each_node_breadth_first(rnp) {
@@ -553,8 +553,8 @@ static void synchronize_rcu_expedited_wait(void)
 					continue;
 				pr_cont(" l=%u:%d-%d:%#lx/%c",
 					rnp->level, rnp->grplo, rnp->grphi,
-					READ_ONCE(rnp->expmask),
-					".T"[!!rnp->exp_tasks]);
+					data_race(rnp->expmask),
+					".T"[!!data_race(rnp->exp_tasks)]);
 			}
 			pr_cont("\n");
 		}
@@ -721,17 +721,20 @@ static void sync_sched_exp_online_cleanup(int cpu)
  */
 static int rcu_print_task_exp_stall(struct rcu_node *rnp)
 {
-	struct task_struct *t;
+	unsigned long flags;
 	int ndetected = 0;
+	struct task_struct *t;
 
-	if (!rnp->exp_tasks)
+	if (!READ_ONCE(rnp->exp_tasks))
 		return 0;
+	raw_spin_lock_irqsave_rcu_node(rnp, flags);
 	t = list_entry(rnp->exp_tasks->prev,
 		       struct task_struct, rcu_node_entry);
 	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
 		pr_cont(" P%d", t->pid);
 		ndetected++;
 	}
+	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	return ndetected;
 }
 
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 097635c..35d77db 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -226,7 +226,7 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
 		WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq);
 	}
 	if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
-		rnp->exp_tasks = &t->rcu_node_entry;
+		WRITE_ONCE(rnp->exp_tasks, &t->rcu_node_entry);
 	WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
 		     !(rnp->qsmask & rdp->grpmask));
 	WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) !=
@@ -500,7 +500,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
 		if (&t->rcu_node_entry == rnp->gp_tasks)
 			WRITE_ONCE(rnp->gp_tasks, np);
 		if (&t->rcu_node_entry == rnp->exp_tasks)
-			rnp->exp_tasks = np;
+			WRITE_ONCE(rnp->exp_tasks, np);
 		if (IS_ENABLED(CONFIG_RCU_BOOST)) {
 			/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
 			drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
@@ -761,7 +761,7 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
 			__func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);
 	pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
 		__func__, READ_ONCE(rnp->gp_tasks), rnp->boost_tasks,
-		rnp->exp_tasks);
+		READ_ONCE(rnp->exp_tasks));
 	pr_info("%s: ->blkd_tasks", __func__);
 	i = 0;
 	list_for_each(lhp, &rnp->blkd_tasks) {
@@ -1036,7 +1036,7 @@ static int rcu_boost_kthread(void *arg)
 	for (;;) {
 		WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING);
 		trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
-		rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
+		rcu_wait(rnp->boost_tasks || READ_ONCE(rnp->exp_tasks));
 		trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
 		WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING);
 		more2boost = rcu_boost(rnp);
-- 
2.9.5

[PATCH tip/core/rcu 05/19] rcu: Add READ_ONCE and data_race() to rcu_node ->boost_tasks

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

The rcu_node structure's ->boost_tasks field is read locklessly, so this
commit adds the READ_ONCE() to one load in order to avoid destructive
compiler optimizations.  The other load is from a diagnostic print,
so data_race() suffices.

This data race was reported by KCSAN.  Not appropriate for backporting
due to failure being unlikely.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree_plugin.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 35d77db..ed6bb46 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -760,7 +760,7 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
 		pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",
 			__func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);
 	pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
-		__func__, READ_ONCE(rnp->gp_tasks), rnp->boost_tasks,
+		__func__, READ_ONCE(rnp->gp_tasks), data_race(rnp->boost_tasks),
 		READ_ONCE(rnp->exp_tasks));
 	pr_info("%s: ->blkd_tasks", __func__);
 	i = 0;
@@ -1036,7 +1036,8 @@ static int rcu_boost_kthread(void *arg)
 	for (;;) {
 		WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING);
 		trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
-		rcu_wait(rnp->boost_tasks || READ_ONCE(rnp->exp_tasks));
+		rcu_wait(READ_ONCE(rnp->boost_tasks) ||
+			 READ_ONCE(rnp->exp_tasks));
 		trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
 		WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING);
 		more2boost = rcu_boost(rnp);
-- 
2.9.5

[PATCH tip/core/rcu 06/19] srcu: Add data_race() to ->srcu_lock_count and ->srcu_unlock_count arrays

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

The srcu_data structure's ->srcu_lock_count and ->srcu_unlock_count arrays
are read and written locklessly, so this commit adds the data_race()
to the diagnostic-print loads from these arrays in order mark them as
known and approved data-racy accesses.

This data race was reported by KCSAN. Not appropriate for backporting due
to failure being unlikely and due to this being used only by rcutorture.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/srcutree.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index ba2b751..6d3ef70 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -1281,8 +1281,8 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
 		struct srcu_data *sdp;
 
 		sdp = per_cpu_ptr(ssp->sda, cpu);
-		u0 = sdp->srcu_unlock_count[!idx];
-		u1 = sdp->srcu_unlock_count[idx];
+		u0 = data_race(sdp->srcu_unlock_count[!idx]);
+		u1 = data_race(sdp->srcu_unlock_count[idx]);
 
 		/*
 		 * Make sure that a lock is always counted if the corresponding
@@ -1290,8 +1290,8 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
 		 */
 		smp_rmb();
 
-		l0 = sdp->srcu_lock_count[!idx];
-		l1 = sdp->srcu_lock_count[idx];
+		l0 = data_race(sdp->srcu_lock_count[!idx]);
+		l1 = data_race(sdp->srcu_lock_count[idx]);
 
 		c0 = l0 - u0;
 		c1 = l1 - u1;
-- 
2.9.5

[PATCH tip/core/rcu 07/19] rcu: Add WRITE_ONCE() to rcu_node ->boost_tasks

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

The rcu_node structure's ->boost_tasks field is read locklessly, so this
commit adds the WRITE_ONCE() to an update in order to provide proper
documentation and READ_ONCE()/WRITE_ONCE() pairing.

This data race was reported by KCSAN.  Not appropriate for backporting
due to failure being unlikely.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree_plugin.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index ed6bb46..664d0aa 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -505,7 +505,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
 			/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
 			drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
 			if (&t->rcu_node_entry == rnp->boost_tasks)
-				rnp->boost_tasks = np;
+				WRITE_ONCE(rnp->boost_tasks, np);
 		}
 
 		/*
@@ -1082,7 +1082,7 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
 	     rnp->qsmask == 0 &&
 	     (ULONG_CMP_GE(jiffies, rnp->boost_time) || rcu_state.cbovld))) {
 		if (rnp->exp_tasks == NULL)
-			rnp->boost_tasks = rnp->gp_tasks;
+			WRITE_ONCE(rnp->boost_tasks, rnp->gp_tasks);
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 		rcu_wake_cond(rnp->boost_kthread_task,
 			      READ_ONCE(rnp->boost_kthread_status));
-- 
2.9.5

[PATCH tip/core/rcu 08/19] rcu: Use data_race() for RCU CPU stall-warning prints

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

Although the accesses used to determine whether or not a stall should
be printed are an integral part of the concurrency algorithm governing
use of the corresponding variables, the values that are simply printed
are ancillary.  As such, it is best to use data_race() for these accesses
in order to provide the greatest latitude in the use of KCSAN for the
other accesses that are an integral part of the algorithm.  This commit
therefore changes the relevant uses of READ_ONCE() to data_race().

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree_stall.h | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 119ed6a..e7da111 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -360,7 +360,7 @@ static void rcu_check_gp_kthread_starvation(void)
 		pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
 		       rcu_state.name, j,
 		       (long)rcu_seq_current(&rcu_state.gp_seq),
-		       READ_ONCE(rcu_state.gp_flags),
+		       data_race(rcu_state.gp_flags),
 		       gp_state_getname(rcu_state.gp_state), rcu_state.gp_state,
 		       gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1);
 		if (gpk) {
@@ -421,10 +421,10 @@ static void print_other_cpu_stall(unsigned long gp_seq)
 			pr_err("INFO: Stall ended before state dump start\n");
 		} else {
 			j = jiffies;
-			gpa = READ_ONCE(rcu_state.gp_activity);
+			gpa = data_race(rcu_state.gp_activity);
 			pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
 			       rcu_state.name, j - gpa, j, gpa,
-			       READ_ONCE(jiffies_till_next_fqs),
+			       data_race(jiffies_till_next_fqs),
 			       rcu_get_root()->qsmask);
 			/* In this case, the current CPU might be at fault. */
 			sched_show_task(current);
@@ -581,23 +581,23 @@ void show_rcu_gp_kthreads(void)
 	struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
 
 	j = jiffies;
-	ja = j - READ_ONCE(rcu_state.gp_activity);
-	jr = j - READ_ONCE(rcu_state.gp_req_activity);
-	jw = j - READ_ONCE(rcu_state.gp_wake_time);
+	ja = j - data_race(rcu_state.gp_activity);
+	jr = j - data_race(rcu_state.gp_req_activity);
+	jw = j - data_race(rcu_state.gp_wake_time);
 	pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_flags %#x\n",
 		rcu_state.name, gp_state_getname(rcu_state.gp_state),
 		rcu_state.gp_state, t ? t->state : 0x1ffffL,
-		ja, jr, jw, (long)READ_ONCE(rcu_state.gp_wake_seq),
-		(long)READ_ONCE(rcu_state.gp_seq),
-		(long)READ_ONCE(rcu_get_root()->gp_seq_needed),
-		READ_ONCE(rcu_state.gp_flags));
+		ja, jr, jw, (long)data_race(rcu_state.gp_wake_seq),
+		(long)data_race(rcu_state.gp_seq),
+		(long)data_race(rcu_get_root()->gp_seq_needed),
+		data_race(rcu_state.gp_flags));
 	rcu_for_each_node_breadth_first(rnp) {
 		if (ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq),
 				 READ_ONCE(rnp->gp_seq_needed)))
 			continue;
 		pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n",
-			rnp->grplo, rnp->grphi, (long)READ_ONCE(rnp->gp_seq),
-			(long)READ_ONCE(rnp->gp_seq_needed));
+			rnp->grplo, rnp->grphi, (long)data_race(rnp->gp_seq),
+			(long)data_race(rnp->gp_seq_needed));
 		if (!rcu_is_leaf_node(rnp))
 			continue;
 		for_each_leaf_node_possible_cpu(rnp, cpu) {
@@ -607,7 +607,7 @@ void show_rcu_gp_kthreads(void)
 					 READ_ONCE(rdp->gp_seq_needed)))
 				continue;
 			pr_info("\tcpu %d ->gp_seq_needed %ld\n",
-				cpu, (long)READ_ONCE(rdp->gp_seq_needed));
+				cpu, (long)data_race(rdp->gp_seq_needed));
 		}
 	}
 	for_each_possible_cpu(cpu) {
-- 
2.9.5

[PATCH tip/core/rcu 09/19] drm: Make drm_dp_mst_dsc_aux_for_port() safe for old compilers

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

Older compilers either want two extra pairs of curly braces around the
initializer for local variable desc, or they want a single pair of curly
braces with nothing inside.  Because current Linux-kernel practice favors
the latter, this commit makes it so.

Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Suggested-by: Joe Perches <joe@perches.com>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 70c4b7a..c409867 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -5494,7 +5494,7 @@ struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port)
 {
 	struct drm_dp_mst_port *immediate_upstream_port;
 	struct drm_dp_mst_port *fec_port;
-	struct drm_dp_desc desc = { 0 };
+	struct drm_dp_desc desc = { };
 	u8 endpoint_fec;
 	u8 endpoint_dsc;
 
-- 
2.9.5

[PATCH tip/core/rcu 10/19] rcu: Expedite first two FQS scans under callback-overload conditions

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

Even if some CPUs have excessive numbers of callbacks, RCU's grace-period
kthread will still wait normally between successive force-quiescent-state
scans.  The first two are the most important, as they are the ones that
enlist aid from the scheduler when overloaded.  This commit therefore
omits the wait before the first and the second force-quiescent-state
scan under callback-overload conditions.

This approach was inspired by a discussion with Jeff Roberson.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree.c | 19 +++++++++++++++----
 kernel/rcu/tree.h |  1 +
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4fd3e0f..7c734b2 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1624,12 +1624,16 @@ static bool rcu_gp_fqs_check_wake(int *gfp)
 {
 	struct rcu_node *rnp = rcu_get_root();
 
-	/* Someone like call_rcu() requested a force-quiescent-state scan. */
+	// If under overload conditions, force an immediate FQS scan.
+	if (*gfp & RCU_GP_FLAG_OVLD)
+		return true;
+
+	// Someone like call_rcu() requested a force-quiescent-state scan.
 	*gfp = READ_ONCE(rcu_state.gp_flags);
 	if (*gfp & RCU_GP_FLAG_FQS)
 		return true;
 
-	/* The current grace period has completed. */
+	// The current grace period has completed.
 	if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
 		return true;
 
@@ -1667,13 +1671,15 @@ static void rcu_gp_fqs(bool first_time)
 static void rcu_gp_fqs_loop(void)
 {
 	bool first_gp_fqs;
-	int gf;
+	int gf = 0;
 	unsigned long j;
 	int ret;
 	struct rcu_node *rnp = rcu_get_root();
 
 	first_gp_fqs = true;
 	j = READ_ONCE(jiffies_till_first_fqs);
+	if (rcu_state.cbovld)
+		gf = RCU_GP_FLAG_OVLD;
 	ret = 0;
 	for (;;) {
 		if (!ret) {
@@ -1698,7 +1704,11 @@ static void rcu_gp_fqs_loop(void)
 			trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
 					       TPS("fqsstart"));
 			rcu_gp_fqs(first_gp_fqs);
-			first_gp_fqs = false;
+			gf = 0;
+			if (first_gp_fqs) {
+				first_gp_fqs = false;
+				gf = rcu_state.cbovld ? RCU_GP_FLAG_OVLD : 0;
+			}
 			trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
 					       TPS("fqsend"));
 			cond_resched_tasks_rcu_qs();
@@ -1718,6 +1728,7 @@ static void rcu_gp_fqs_loop(void)
 				j = 1;
 			else
 				j = rcu_state.jiffies_force_qs - j;
+			gf = 0;
 		}
 	}
 }
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 9dc2ec0..44edd0a 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -359,6 +359,7 @@ struct rcu_state {
 /* Values for rcu_state structure's gp_flags field. */
 #define RCU_GP_FLAG_INIT 0x1	/* Need grace-period initialization. */
 #define RCU_GP_FLAG_FQS  0x2	/* Need grace-period quiescent-state forcing. */
+#define RCU_GP_FLAG_OVLD 0x4	/* Experiencing callback overload. */
 
 /* Values for rcu_state structure's gp_state field. */
 #define RCU_GP_IDLE	 0	/* Initial state and no GP in progress. */
-- 
2.9.5

[PATCH tip/core/rcu 11/19] rcu: Fix the (t=0 jiffies) false positive

[paulmck]

From: Zhaolong Zhang <zhangzl2013@126.com>

It is possible that an over-long grace period will end while the RCU
CPU stall warning message is printing.  In this case, the estimate of
the offending grace period's duration can be erroneous due to refetching
of rcu_state.gp_start, which will now be the time of the newly started
grace period.  Computation of this duration clearly needs to use the
start time for the old over-long grace period, not the fresh new one.
This commit avoids such errors by causing both print_other_cpu_stall() and
print_cpu_stall() to reuse the value previously fetched by their caller.

Signed-off-by: Zhaolong Zhang <zhangzl2013@126.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree_stall.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index e7da111..3a7bc99 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -371,7 +371,7 @@ static void rcu_check_gp_kthread_starvation(void)
 	}
 }
 
-static void print_other_cpu_stall(unsigned long gp_seq)
+static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 {
 	int cpu;
 	unsigned long flags;
@@ -408,7 +408,7 @@ static void print_other_cpu_stall(unsigned long gp_seq)
 	for_each_possible_cpu(cpu)
 		totqlen += rcu_get_n_cbs_cpu(cpu);
 	pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n",
-	       smp_processor_id(), (long)(jiffies - rcu_state.gp_start),
+	       smp_processor_id(), (long)(jiffies - gps),
 	       (long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
 	if (ndetected) {
 		rcu_dump_cpu_stacks();
@@ -442,7 +442,7 @@ static void print_other_cpu_stall(unsigned long gp_seq)
 	rcu_force_quiescent_state();  /* Kick them all. */
 }
 
-static void print_cpu_stall(void)
+static void print_cpu_stall(unsigned long gps)
 {
 	int cpu;
 	unsigned long flags;
@@ -467,7 +467,7 @@ static void print_cpu_stall(void)
 	for_each_possible_cpu(cpu)
 		totqlen += rcu_get_n_cbs_cpu(cpu);
 	pr_cont("\t(t=%lu jiffies g=%ld q=%lu)\n",
-		jiffies - rcu_state.gp_start,
+		jiffies - gps,
 		(long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
 
 	rcu_check_gp_kthread_starvation();
@@ -546,7 +546,7 @@ static void check_cpu_stall(struct rcu_data *rdp)
 	    cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
 
 		/* We haven't checked in, so go dump stack. */
-		print_cpu_stall();
+		print_cpu_stall(gps);
 		if (rcu_cpu_stall_ftrace_dump)
 			rcu_ftrace_dump(DUMP_ALL);
 
@@ -555,7 +555,7 @@ static void check_cpu_stall(struct rcu_data *rdp)
 		   cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
 
 		/* They had a few time units to dump stack, so complain. */
-		print_other_cpu_stall(gs2);
+		print_other_cpu_stall(gs2, gps);
 		if (rcu_cpu_stall_ftrace_dump)
 			rcu_ftrace_dump(DUMP_ALL);
 	}
-- 
2.9.5

[PATCH tip/core/rcu 12/19] Revert "rculist: Describe variadic macro argument in a Sphinx-compatible way"

[paulmck]

From: Jonathan Neuschäfer <j.neuschaefer@gmx.net>

This reverts commit f452ee096d95482892b101bde4fd037fa025d3cc.

The workaround became unnecessary with commit 43756e347f21
("scripts/kernel-doc: Add support for named variable macro arguments").

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/rculist.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 8214cdc..7375bb3 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -371,7 +371,7 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  * @pos:	the type * to use as a loop cursor.
  * @head:	the head for your list.
  * @member:	the name of the list_head within the struct.
- * @cond...:	optional lockdep expression if called from non-RCU protection.
+ * @cond:	optional lockdep expression if called from non-RCU protection.
  *
  * This list-traversal primitive may safely run concurrently with
  * the _rcu list-mutation primitives such as list_add_rcu()
@@ -646,7 +646,7 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
  * @pos:	the type * to use as a loop cursor.
  * @head:	the head for your list.
  * @member:	the name of the hlist_node within the struct.
- * @cond...:	optional lockdep expression if called from non-RCU protection.
+ * @cond:	optional lockdep expression if called from non-RCU protection.
  *
  * This list-traversal primitive may safely run concurrently with
  * the _rcu list-mutation primitives such as hlist_add_head_rcu()
-- 
2.9.5

[PATCH tip/core/rcu 13/19] rcu: Get rid of some doc warnings in update.c

[paulmck]

From: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

This commit escapes *ret, because otherwise the documentation system
thinks that this is an incomplete emphasis block:

	./kernel/rcu/update.c:65: WARNING: Inline emphasis start-string without end-string.
	./kernel/rcu/update.c:65: WARNING: Inline emphasis start-string without end-string.
	./kernel/rcu/update.c:70: WARNING: Inline emphasis start-string without end-string.
	./kernel/rcu/update.c:82: WARNING: Inline emphasis start-string without end-string.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/update.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 28a8bdc..72461dd8 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -63,12 +63,12 @@ module_param(rcu_normal_after_boot, int, 0);
  * rcu_read_lock_held_common() - might we be in RCU-sched read-side critical section?
  * @ret:	Best guess answer if lockdep cannot be relied on
  *
- * Returns true if lockdep must be ignored, in which case *ret contains
+ * Returns true if lockdep must be ignored, in which case ``*ret`` contains
  * the best guess described below.  Otherwise returns false, in which
- * case *ret tells the caller nothing and the caller should instead
+ * case ``*ret`` tells the caller nothing and the caller should instead
  * consult lockdep.
  *
- * If CONFIG_DEBUG_LOCK_ALLOC is selected, set *ret to nonzero iff in an
+ * If CONFIG_DEBUG_LOCK_ALLOC is selected, set ``*ret`` to nonzero iff in an
  * RCU-sched read-side critical section.  In absence of
  * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
  * critical section unless it can prove otherwise.  Note that disabling
@@ -82,7 +82,7 @@ module_param(rcu_normal_after_boot, int, 0);
  *
  * Note that if the CPU is in the idle loop from an RCU point of view (ie:
  * that we are in the section between rcu_idle_enter() and rcu_idle_exit())
- * then rcu_read_lock_held() sets *ret to false even if the CPU did an
+ * then rcu_read_lock_held() sets ``*ret`` to false even if the CPU did an
  * rcu_read_lock().  The reason for this is that RCU ignores CPUs that are
  * in such a section, considering these as in extended quiescent state,
  * so such a CPU is effectively never in an RCU read-side critical section
-- 
2.9.5

[PATCH tip/core/rcu 14/19] rcu: Mark rcu_state.gp_seq to detect more concurrent writes

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

The rcu_state structure's gp_seq field is only to be modified by the RCU
grace-period kthread, which is single-threaded.  This commit therefore
enlists KCSAN's help in enforcing this restriction.  This commit applies
KCSAN-specific primitives, so cannot go upstream until KCSAN does.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 7c734b2..09ccc29 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1230,7 +1230,7 @@ static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
 		trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
 		goto unlock_out;
 	}
-	trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("newreq"));
+	trace_rcu_grace_period(rcu_state.name, data_race(rcu_state.gp_seq), TPS("newreq"));
 	ret = true;  /* Caller must wake GP kthread. */
 unlock_out:
 	/* Push furthest requested GP to leaf node and rcu_data structure. */
@@ -1519,6 +1519,7 @@ static bool rcu_gp_init(void)
 	record_gp_stall_check_time();
 	/* Record GP times before starting GP, hence rcu_seq_start(). */
 	rcu_seq_start(&rcu_state.gp_seq);
+	ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
 	trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));
 	raw_spin_unlock_irq_rcu_node(rnp);
 
@@ -1805,6 +1806,7 @@ static void rcu_gp_cleanup(void)
 	/* Declare grace period done, trace first to use old GP number. */
 	trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end"));
 	rcu_seq_end(&rcu_state.gp_seq);
+	ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
 	rcu_state.gp_state = RCU_GP_IDLE;
 	/* Check for GP requests since above loop. */
 	rdp = this_cpu_ptr(&rcu_data);
-- 
2.9.5

[PATCH tip/core/rcu 15/19] rcu: Replace assigned pointer ret value by corresponding boolean value

[paulmck]

From: Jules Irenge <jbi.octave@gmail.com>

Coccinelle reports warnings at rcu_read_lock_held_common()

WARNING: Assignment of 0/1 to bool variable

To fix this,
the assigned  pointer ret values are replaced by corresponding boolean value.
Given that ret is a pointer of bool type

Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/update.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 72461dd8..17f2356 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -98,15 +98,15 @@ module_param(rcu_normal_after_boot, int, 0);
 static bool rcu_read_lock_held_common(bool *ret)
 {
 	if (!debug_lockdep_rcu_enabled()) {
-		*ret = 1;
+		*ret = true;
 		return true;
 	}
 	if (!rcu_is_watching()) {
-		*ret = 0;
+		*ret = false;
 		return true;
 	}
 	if (!rcu_lockdep_current_cpu_online()) {
-		*ret = 0;
+		*ret = false;
 		return true;
 	}
 	return false;
-- 
2.9.5

[PATCH tip/core/rcu 16/19] rcu: Replace 1 by true

[paulmck]

From: Jules Irenge <jbi.octave@gmail.com>

Coccinelle reports a warning at use_softirq declaration

WARNING: Assignment of 0/1 to bool variable

The root cause is
use_softirq a variable of bool type is initialised with the integer 1
Replacing 1 with value true solve the issue.

Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 09ccc29..97c0b47 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -113,7 +113,7 @@ static struct rcu_state rcu_state = {
 static bool dump_tree;
 module_param(dump_tree, bool, 0444);
 /* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */
-static bool use_softirq = 1;
+static bool use_softirq = true;
 module_param(use_softirq, bool, 0444);
 /* Control rcu_node-tree auto-balancing at boot time. */
 static bool rcu_fanout_exact;
-- 
2.9.5

[PATCH tip/core/rcu 17/19] rcu: Convert ULONG_CMP_GE() to time_after() for jiffy comparison

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

This commit converts the ULONG_CMP_GE() in rcu_gp_fqs_loop() to
time_after() to reflect the fact that it is comparing a timestamp to
the jiffies counter.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 97c0b47..66321cc 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1700,7 +1700,7 @@ static void rcu_gp_fqs_loop(void)
 		    !rcu_preempt_blocked_readers_cgp(rnp))
 			break;
 		/* If time for quiescent-state forcing, do it. */
-		if (ULONG_CMP_GE(jiffies, rcu_state.jiffies_force_qs) ||
+		if (!time_after(rcu_state.jiffies_force_qs, jiffies) ||
 		    (gf & RCU_GP_FLAG_FQS)) {
 			trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
 					       TPS("fqsstart"));
-- 
2.9.5

[PATCH tip/core/rcu 18/19] rcu: Convert rcu_initiate_boost() ULONG_CMP_GE() to time_after()

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

This commit converts the ULONG_CMP_GE() in rcu_initiate_boost() to
time_after() to reflect the fact that it is comparing a timestamp to
the jiffies counter.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree_plugin.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 664d0aa..5cd27c2 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1080,7 +1080,7 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
 	    (rnp->gp_tasks != NULL &&
 	     rnp->boost_tasks == NULL &&
 	     rnp->qsmask == 0 &&
-	     (ULONG_CMP_GE(jiffies, rnp->boost_time) || rcu_state.cbovld))) {
+	     (!time_after(rnp->boost_time, jiffies) || rcu_state.cbovld))) {
 		if (rnp->exp_tasks == NULL)
 			WRITE_ONCE(rnp->boost_tasks, rnp->gp_tasks);
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-- 
2.9.5

[PATCH tip/core/rcu 19/19] rcu: Convert rcu_nohz_full_cpu() ULONG_CMP_LT() to time_before()

[paulmck]

From: "Paul E. McKenney" <paulmck@kernel.org>

This commit converts the ULONG_CMP_LT() in rcu_nohz_full_cpu() to
time_before() to reflect the fact that it is comparing a timestamp to
the jiffies counter.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree_plugin.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 5cd27c2..5771e32 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2537,7 +2537,7 @@ static bool rcu_nohz_full_cpu(void)
 #ifdef CONFIG_NO_HZ_FULL
 	if (tick_nohz_full_cpu(smp_processor_id()) &&
 	    (!rcu_gp_in_progress() ||
-	     ULONG_CMP_LT(jiffies, READ_ONCE(rcu_state.gp_start) + HZ)))
+	     time_before(jiffies, READ_ONCE(rcu_state.gp_start) + HZ)))
 		return true;
 #endif /* #ifdef CONFIG_NO_HZ_FULL */
 	return false;
-- 
2.9.5

Re: [PATCH tip/core/rcu 0/19] Miscellaneous fixes for v5.8

[Andrew Morton]

On Wed, 15 Apr 2020 10:10:17 -0700 "Paul E. McKenney" <paulmck@kernel.org> wrote:

> Subject: [PATCH tip/core/rcu 0/19] Miscellaneous fixes for v5.8

I was hoping we could get at least the data_race() implementation
into 5.7-rc1 - I'm sitting on a pile of patches which use it.  Oh well,
next time.

Re: [PATCH tip/core/rcu 0/19] Miscellaneous fixes for v5.8

[Paul E. McKenney]

On Wed, Apr 15, 2020 at 10:21:23AM -0700, Andrew Morton wrote:
> On Wed, 15 Apr 2020 10:10:17 -0700 "Paul E. McKenney" <paulmck@kernel.org> wrote:
> 
> > Subject: [PATCH tip/core/rcu 0/19] Miscellaneous fixes for v5.8
> 
> I was hoping we could get at least the data_race() implementation
> into 5.7-rc1 - I'm sitting on a pile of patches which use it.  Oh well,
> next time.

I could put the stubs somewhere more visible, if that would help.
Me, I ran out of patience, so you are a better man than am I!  ;-)

							Thanx, Paul