From: Uladzislau Rezki (Sony) <urezki@gmail.com>
Date: Fri, 2 Dec 2022 13:18:37 +0000 (+0100)
Subject: rcu/kvfree: Use READ_ONCE() when access to krcp->head
X-Git-Tag: io_uring-6.3-2023-03-03~30^2~1^3~3
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=9627456101ec9bb502daae7276e5141f66a9ddd1;p=linux-block.git

rcu/kvfree: Use READ_ONCE() when access to krcp->head

The need_offload_krc() function is now lock-free, which gives the
compiler freedom to load old values from plain C-language loads from
the kfree_rcu_cpu struture's ->head pointer.  This commit therefore
applied READ_ONCE() to these loads.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 735312f78e98..02551e0e1132 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3165,7 +3165,7 @@ need_offload_krc(struct kfree_rcu_cpu *krcp)
 		if (!list_empty(&krcp->bulk_head[i]))
 			return true;
 
-	return !!krcp->head;
+	return !!READ_ONCE(krcp->head);
 }
 
 static void
@@ -3206,7 +3206,7 @@ static void kfree_rcu_monitor(struct work_struct *work)
 		// in that case the monitor work is rearmed.
 		if ((!list_empty(&krcp->bulk_head[0]) && list_empty(&krwp->bulk_head_free[0])) ||
 			(!list_empty(&krcp->bulk_head[1]) && list_empty(&krwp->bulk_head_free[1])) ||
-				(krcp->head && !krwp->head_free)) {
+				(READ_ONCE(krcp->head) && !krwp->head_free)) {
 
 			// Channel 1 corresponds to the SLAB-pointer bulk path.
 			// Channel 2 corresponds to vmalloc-pointer bulk path.