[PATCH rcu 0/2] RCU nocb changes for v6.17

[PATCH rcu 0/2] RCU nocb changes for v6.17

[neeraj.upadhyay]

From: "Neeraj Upadhyay (AMD)" <neeraj.upadhyay@kernel.org>

Hello,

This patch series contains following updates to the RCU nocb code (rebased
on v6.16-rc3):

Frederic Weisbecker (1):
  rcu/nocb: Dump gp state even if rdp gp itself is not offloaded

Zqiang (1):
  rcu/nocb: Fix possible invalid rdp's->nocb_cb_kthread pointer access

 kernel/rcu/tree_nocb.h  | 8 +++++---
 kernel/rcu/tree_stall.h | 3 +--
 2 files changed, 6 insertions(+), 5 deletions(-)

-- 
2.40.1

[PATCH rcu 1/2] rcu/nocb: Dump gp state even if rdp gp itself is not offloaded

[neeraj.upadhyay]

From: Frederic Weisbecker <frederic@kernel.org>

When a stall is detected, the state of each NOCB CPU is dumped along
with the state of each NOCB group. The latter part however is
incidentally ignored if the NOCB group leader happens not to be
offloaded itself.

Fix this to make sure related precious informations aren't lost over
a stall report.

Reported-by: "Paul E. McKenney" <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: "Paul E. McKenney" <paulmck@kernel.org>
Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.upadhyay@kernel.org>
---
 kernel/rcu/tree_nocb.h  | 3 +++
 kernel/rcu/tree_stall.h | 3 +--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index b473ff056f49..cb29b6bb0ed4 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1564,6 +1564,9 @@ static void show_rcu_nocb_state(struct rcu_data *rdp)
 	if (rdp->nocb_gp_rdp == rdp)
 		show_rcu_nocb_gp_state(rdp);
 
+	if (!rcu_segcblist_is_offloaded(&rdp->cblist))
+		return;
+
 	nocb_next_rdp = list_next_or_null_rcu(&rdp->nocb_gp_rdp->nocb_head_rdp,
 					      &rdp->nocb_entry_rdp,
 					      typeof(*rdp),
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 486c00536207..4fa64c959083 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -953,8 +953,7 @@ void show_rcu_gp_kthreads(void)
 	for_each_possible_cpu(cpu) {
 		rdp = per_cpu_ptr(&rcu_data, cpu);
 		cbs += data_race(READ_ONCE(rdp->n_cbs_invoked));
-		if (rcu_segcblist_is_offloaded(&rdp->cblist))
-			show_rcu_nocb_state(rdp);
+		show_rcu_nocb_state(rdp);
 	}
 	pr_info("RCU callbacks invoked since boot: %lu\n", cbs);
 	show_rcu_tasks_gp_kthreads();
-- 
2.40.1

[PATCH rcu 2/2] rcu/nocb: Fix possible invalid rdp's->nocb_cb_kthread pointer access

[neeraj.upadhyay]

From: Zqiang <qiang.zhang1211@gmail.com>

In the preparation stage of CPU online, if the corresponding
the rdp's->nocb_cb_kthread does not exist, will be created,
there is a situation where the rdp's rcuop kthreads creation fails,
and then de-offload this CPU's rdp, does not assign this CPU's
rdp->nocb_cb_kthread pointer, but this rdp's->nocb_gp_rdp and
rdp's->rdp_gp->nocb_gp_kthread is still valid.

This will cause the subsequent re-offload operation of this offline
CPU, which will pass the conditional check and the kthread_unpark()
will access invalid rdp's->nocb_cb_kthread pointer.

This commit therefore use rdp's->nocb_gp_kthread instead of
rdp_gp's->nocb_gp_kthread for safety check.

Signed-off-by: Zqiang <qiang.zhang1211@gmail.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.upadhyay@kernel.org>
---
 kernel/rcu/tree_nocb.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index cb29b6bb0ed4..08eb9b0e2fab 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1146,7 +1146,6 @@ static bool rcu_nocb_rdp_offload_wait_cond(struct rcu_data *rdp)
 static int rcu_nocb_rdp_offload(struct rcu_data *rdp)
 {
 	int wake_gp;
-	struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
 
 	WARN_ON_ONCE(cpu_online(rdp->cpu));
 	/*
@@ -1156,7 +1155,7 @@ static int rcu_nocb_rdp_offload(struct rcu_data *rdp)
 	if (!rdp->nocb_gp_rdp)
 		return -EINVAL;
 
-	if (WARN_ON_ONCE(!rdp_gp->nocb_gp_kthread))
+	if (WARN_ON_ONCE(!rdp->nocb_gp_kthread))
 		return -EINVAL;
 
 	pr_info("Offloading %d\n", rdp->cpu);
@@ -1166,7 +1165,7 @@ static int rcu_nocb_rdp_offload(struct rcu_data *rdp)
 
 	wake_gp = rcu_nocb_queue_toggle_rdp(rdp);
 	if (wake_gp)
-		wake_up_process(rdp_gp->nocb_gp_kthread);
+		wake_up_process(rdp->nocb_gp_kthread);
 
 	swait_event_exclusive(rdp->nocb_state_wq,
 			      rcu_nocb_rdp_offload_wait_cond(rdp));
-- 
2.40.1