rcu: Break rcu_node_0 --> &rq->__lock order

Commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in
do_set_cpus_allowed()") added a kfree() call to free any user
provided affinity mask, if present. It was changed later to use
kfree_rcu() in commit 9a5418bc48ba ("sched/core: Use kfree_rcu()
in do_set_cpus_allowed()") to avoid a circular locking dependency
problem.

It turns out that even kfree_rcu() isn't safe for avoiding
circular locking problem. As reported by kernel test robot,
the following circular locking dependency now exists:

  &rdp->nocb_lock --> rcu_node_0 --> &rq->__lock

Solve this by breaking the rcu_node_0 --> &rq->__lock chain by moving
the resched_cpu() out from under rcu_node lock.

[peterz: heavily borrowed from Waiman's Changelog]
[paulmck: applied Z qiang feedback]

Fixes: 851a723e45d1 ("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()")
Reported-by: kernel test robot <oliver.sang@intel.com>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/oe-lkp/202310302207.a25f1a30-oliver.sang@intel.com
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

1 files changed, 25 insertions, 11 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 700524726079..77e7a0dc722a 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -755,14 +755,19 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp)
 }
 
 /*
- * Return true if the specified CPU has passed through a quiescent
- * state by virtue of being in or having passed through an dynticks
- * idle state since the last call to dyntick_save_progress_counter()
- * for this same CPU, or by virtue of having been offline.
+ * Returns positive if the specified CPU has passed through a quiescent state
+ * by virtue of being in or having passed through an dynticks idle state since
+ * the last call to dyntick_save_progress_counter() for this same CPU, or by
+ * virtue of having been offline.
+ *
+ * Returns negative if the specified CPU needs a force resched.
+ *
+ * Returns zero otherwise.
  */
 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 {
 	unsigned long jtsq;
+	int ret = 0;
 	struct rcu_node *rnp = rdp->mynode;
 
 	/*
@@ -848,8 +853,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 	    (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) ||
 	     rcu_state.cbovld)) {
 		WRITE_ONCE(rdp->rcu_urgent_qs, true);
-		resched_cpu(rdp->cpu);
 		WRITE_ONCE(rdp->last_fqs_resched, jiffies);
+		ret = -1;
 	}
 
 	/*
@@ -862,8 +867,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 	if (time_after(jiffies, rcu_state.jiffies_resched)) {
 		if (time_after(jiffies,
 			       READ_ONCE(rdp->last_fqs_resched) + jtsq)) {
-			resched_cpu(rdp->cpu);
 			WRITE_ONCE(rdp->last_fqs_resched, jiffies);
+			ret = -1;
 		}
 		if (IS_ENABLED(CONFIG_IRQ_WORK) &&
 		    !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
@@ -892,7 +897,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 		}
 	}
 
-	return 0;
+	return ret;
 }
 
 /* Trace-event wrapper function for trace_rcu_future_grace_period.  */
@@ -2271,15 +2276,15 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
 {
 	int cpu;
 	unsigned long flags;
-	unsigned long mask;
-	struct rcu_data *rdp;
 	struct rcu_node *rnp;
 
 	rcu_state.cbovld = rcu_state.cbovldnext;
 	rcu_state.cbovldnext = false;
 	rcu_for_each_leaf_node(rnp) {
+		unsigned long mask = 0;
+		unsigned long rsmask = 0;
+
 		cond_resched_tasks_rcu_qs();
-		mask = 0;
 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 		rcu_state.cbovldnext |= !!rnp->cbovldmask;
 		if (rnp->qsmask == 0) {
@@ -2297,11 +2302,17 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
 			continue;
 		}
 		for_each_leaf_node_cpu_mask(rnp, cpu, rnp->qsmask) {
+			struct rcu_data *rdp;
+			int ret;
+
 			rdp = per_cpu_ptr(&rcu_data, cpu);
-			if (f(rdp)) {
+			ret = f(rdp);
+			if (ret > 0) {
 				mask |= rdp->grpmask;
 				rcu_disable_urgency_upon_qs(rdp);
 			}
+			if (ret < 0)
+				rsmask |= rdp->grpmask;
 		}
 		if (mask != 0) {
 			/* Idle/offline CPUs, report (releases rnp->lock). */
@@ -2310,6 +2321,9 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
 			/* Nothing to do here, so just drop the lock. */
 			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 		}
+
+		for_each_leaf_node_cpu_mask(rnp, cpu, rsmask)
+			resched_cpu(cpu);
 	}
 }