From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Zqiang <qiang.zhang1211@gmail.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	"Neeraj Upadhyay (AMD)" <neeraj.upadhyay@kernel.org>,
	Jianqiang kang <jianqkang@sina.cn>
Subject: [PATCH 6.1 466/481] rcu/nocb: Fix possible invalid rdps->nocb_cb_kthread pointer access
Date: Mon, 23 Mar 2026 14:47:28 +0100
Message-ID: <20260323134536.570791934@linuxfoundation.org>
In-Reply-To: <20260323134525.256603107@linuxfoundation.org>
References: <20260323134525.256603107@linuxfoundation.org>
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6.1-stable review patch.  If anyone has any objections, please let me know.

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

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

[ Upstream commit 1bba3900ca18bdae28d1b9fa10f16a8f8cb2ada1 ]

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>
[ Minor conflict resolved. ]
Signed-off-by: Jianqiang kang <jianqkang@sina.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/rcu/tree_nocb.h |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1112,7 +1112,6 @@ static long rcu_nocb_rdp_offload(void *a
 	struct rcu_segcblist *cblist = &rdp->cblist;
 	unsigned long flags;
 	int wake_gp;
-	struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
 
 	WARN_ON_ONCE(rdp->cpu != raw_smp_processor_id());
 	/*
@@ -1122,7 +1121,7 @@ static long rcu_nocb_rdp_offload(void *a
 	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);
@@ -1151,7 +1150,7 @@ static long rcu_nocb_rdp_offload(void *a
 	 */
 	wake_gp = rdp_offload_toggle(rdp, true, flags);
 	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_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB) &&
 			      rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP));