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authorPeter Zijlstra <peterz@infradead.org>2023-10-31 09:53:08 +0100
committerFrederic Weisbecker <frederic@kernel.org>2023-11-01 21:39:58 +0100
commit85d68222ddc5f4522e456d97d201166acb50f716 (patch)
treea4104a2c1aa357fc29666bd774daebade3aaffd4 /kernel
parent2656821f1f202d58224551b71eff41aafd1edf8b (diff)
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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/rcu/tree.c36
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);
}
}