This is a note to let you know that I've just added the patch titled
rcu: Break rcu_node_0 --> &rq->__lock order
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
rcu-break-rcu_node_0-rq-__lock-order.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 0e1e7911cf400c7f6ba161b4d3b87e9170ce450d
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Tue Oct 31 09:53:08 2023 +0100
rcu: Break rcu_node_0 --> &rq->__lock order
[ Upstream commit 85d68222ddc5f4522e456d97d201166acb50f716 ]
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@xxxxxxxxx>
Acked-by: Waiman Long <longman@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/oe-lkp/202310302207.a25f1a30-oliver.sang@xxxxxxxxx
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 7b4517dc46579..92a090e161865 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. */
@@ -2270,15 +2275,15 @@ 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) {
@@ -2296,11 +2301,17 @@ 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). */
@@ -2309,6 +2320,9 @@ 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);
}
}
