linux-kernel - [PATCH 2/7] RDMA: hfi1: fix possible divide-by-zero in find_hw_thread

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Message-ID: <20250604193947.11834-3-yury.norov@gmail.com>
Date: Wed,  4 Jun 2025 15:39:38 -0400
From: Yury Norov <yury.norov@...il.com>
To: Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Leon Romanovsky <leon@...nel.org>,
	Yury Norov <yury.norov@...il.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-rdma@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/7] RDMA: hfi1: fix possible divide-by-zero in find_hw_thread_mask()

From: "Yury Norov [NVIDIA]" <yury.norov@...il.com>

The function divides number of online CPUs by num_core_siblings, and
later checks the divider by zero. This implies a possibility to get
and divide-by-zero runtime error. Fix it by moving the check prior to
division. This also helps to save one indentation level.

Signed-off-by: Yury Norov [NVIDIA] <yury.norov@...il.com>
---
 drivers/infiniband/hw/hfi1/affinity.c | 44 +++++++++++++++------------
 1 file changed, 24 insertions(+), 20 deletions(-)

diff --git a/drivers/infiniband/hw/hfi1/affinity.c b/drivers/infiniband/hw/hfi1/affinity.c
index 7ead8746b79b..f2c530ab85a5 100644
--- a/drivers/infiniband/hw/hfi1/affinity.c
+++ b/drivers/infiniband/hw/hfi1/affinity.c
@@ -964,31 +964,35 @@ static void find_hw_thread_mask(uint hw_thread_no, cpumask_var_t hw_thread_mask,
 				struct hfi1_affinity_node_list *affinity)
 {
 	int possible, curr_cpu, i;
-	uint num_cores_per_socket = node_affinity.num_online_cpus /
+	uint num_cores_per_socket;
+
+	cpumask_copy(hw_thread_mask, &affinity->proc.mask);
+
+	if (affinity->num_core_siblings == 0)
+		return;
+
+	num_cores_per_socket = node_affinity.num_online_cpus /
 					affinity->num_core_siblings /
 						node_affinity.num_online_nodes;
 
-	cpumask_copy(hw_thread_mask, &affinity->proc.mask);
-	if (affinity->num_core_siblings > 0) {
-		/* Removing other siblings not needed for now */
-		possible = cpumask_weight(hw_thread_mask);
-		curr_cpu = cpumask_first(hw_thread_mask);
-		for (i = 0;
-		     i < num_cores_per_socket * node_affinity.num_online_nodes;
-		     i++)
-			curr_cpu = cpumask_next(curr_cpu, hw_thread_mask);
-
-		for (; i < possible; i++) {
-			cpumask_clear_cpu(curr_cpu, hw_thread_mask);
-			curr_cpu = cpumask_next(curr_cpu, hw_thread_mask);
-		}
+	/* Removing other siblings not needed for now */
+	possible = cpumask_weight(hw_thread_mask);
+	curr_cpu = cpumask_first(hw_thread_mask);
+	for (i = 0;
+	     i < num_cores_per_socket * node_affinity.num_online_nodes;
+	     i++)
+		curr_cpu = cpumask_next(curr_cpu, hw_thread_mask);
 
-		/* Identifying correct HW threads within physical cores */
-		cpumask_shift_left(hw_thread_mask, hw_thread_mask,
-				   num_cores_per_socket *
-				   node_affinity.num_online_nodes *
-				   hw_thread_no);
+	for (; i < possible; i++) {
+		cpumask_clear_cpu(curr_cpu, hw_thread_mask);
+		curr_cpu = cpumask_next(curr_cpu, hw_thread_mask);
 	}
+
+	/* Identifying correct HW threads within physical cores */
+	cpumask_shift_left(hw_thread_mask, hw_thread_mask,
+			   num_cores_per_socket *
+			   node_affinity.num_online_nodes *
+			   hw_thread_no);
 }
 
 int hfi1_get_proc_affinity(int node)
-- 
2.43.0