mm/vmalloc: fix data race in show_numa_info()

The following data-race was found in show_numa_info():

==================================================================
BUG: KCSAN: data-race in vmalloc_info_show / vmalloc_info_show

read to 0xffff88800971fe30 of 4 bytes by task 8289 on cpu 0:
 show_numa_info mm/vmalloc.c:4936 [inline]
 vmalloc_info_show+0x5a8/0x7e0 mm/vmalloc.c:5016
 seq_read_iter+0x373/0xb40 fs/seq_file.c:230
 proc_reg_read_iter+0x11e/0x170 fs/proc/inode.c:299
....

write to 0xffff88800971fe30 of 4 bytes by task 8287 on cpu 1:
 show_numa_info mm/vmalloc.c:4934 [inline]
 vmalloc_info_show+0x38f/0x7e0 mm/vmalloc.c:5016
 seq_read_iter+0x373/0xb40 fs/seq_file.c:230
 proc_reg_read_iter+0x11e/0x170 fs/proc/inode.c:299
....

value changed: 0x0000008f -> 0x00000000
==================================================================

According to this report,there is a read/write data-race because
m->private is accessible to multiple CPUs.  To fix this, instead of
allocating the heap in proc_vmalloc_init() and passing the heap address to
m->private, vmalloc_info_show() should allocate the heap.

Link: https://lkml.kernel.org/r/20250508165620.15321-1-aha310510@gmail.com
Fixes: 8e1d743f2c26 ("mm: vmalloc: support multiple nodes in vmallocinfo")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
Suggested-by: Eric Dumazet <edumazet@google.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 35 insertions, 28 deletions

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 701ea4ec8950..49df04e1fbe1 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3109,7 +3109,7 @@ static void clear_vm_uninitialized_flag(struct vm_struct *vm)
 	/*
 	 * Before removing VM_UNINITIALIZED,
 	 * we should make sure that vm has proper values.
-	 * Pair with smp_rmb() in show_numa_info().
+	 * Pair with smp_rmb() in vread_iter() and vmalloc_info_show().
 	 */
 	smp_wmb();
 	vm->flags &= ~VM_UNINITIALIZED;
@@ -4939,28 +4939,29 @@ bool vmalloc_dump_obj(void *object)
 #endif
 
 #ifdef CONFIG_PROC_FS
-static void show_numa_info(struct seq_file *m, struct vm_struct *v)
-{
-	if (IS_ENABLED(CONFIG_NUMA)) {
-		unsigned int nr, *counters = m->private;
-		unsigned int step = 1U << vm_area_page_order(v);
 
-		if (!counters)
-			return;
+/*
+ * Print number of pages allocated on each memory node.
+ *
+ * This function can only be called if CONFIG_NUMA is enabled
+ * and VM_UNINITIALIZED bit in v->flags is disabled.
+ */
+static void show_numa_info(struct seq_file *m, struct vm_struct *v,
+				 unsigned int *counters)
+{
+	unsigned int nr;
+	unsigned int step = 1U << vm_area_page_order(v);
 
-		if (v->flags & VM_UNINITIALIZED)
-			return;
-		/* Pair with smp_wmb() in clear_vm_uninitialized_flag() */
-		smp_rmb();
+	if (!counters)
+		return;
 
-		memset(counters, 0, nr_node_ids * sizeof(unsigned int));
+	memset(counters, 0, nr_node_ids * sizeof(unsigned int));
 
-		for (nr = 0; nr < v->nr_pages; nr += step)
-			counters[page_to_nid(v->pages[nr])] += step;
-		for_each_node_state(nr, N_HIGH_MEMORY)
-			if (counters[nr])
-				seq_printf(m, " N%u=%u", nr, counters[nr]);
-	}
+	for (nr = 0; nr < v->nr_pages; nr += step)
+		counters[page_to_nid(v->pages[nr])] += step;
+	for_each_node_state(nr, N_HIGH_MEMORY)
+		if (counters[nr])
+			seq_printf(m, " N%u=%u", nr, counters[nr]);
 }
 
 static void show_purge_info(struct seq_file *m)
@@ -4984,6 +4985,10 @@ static int vmalloc_info_show(struct seq_file *m, void *p)
 	struct vmap_node *vn;
 	struct vmap_area *va;
 	struct vm_struct *v;
+	unsigned int *counters;
+
+	if (IS_ENABLED(CONFIG_NUMA))
+		counters = kmalloc(nr_node_ids * sizeof(unsigned int), GFP_KERNEL);
 
 	for_each_vmap_node(vn) {
 		spin_lock(&vn->busy.lock);
@@ -4998,6 +5003,11 @@ static int vmalloc_info_show(struct seq_file *m, void *p)
 			}
 
 			v = va->vm;
+			if (v->flags & VM_UNINITIALIZED)
+				continue;
+
+			/* Pair with smp_wmb() in clear_vm_uninitialized_flag() */
+			smp_rmb();
 
 			seq_printf(m, "0x%pK-0x%pK %7ld",
 				v->addr, v->addr + v->size, v->size);
@@ -5032,7 +5042,9 @@ static int vmalloc_info_show(struct seq_file *m, void *p)
 			if (is_vmalloc_addr(v->pages))
 				seq_puts(m, " vpages");
 
-			show_numa_info(m, v);
+			if (IS_ENABLED(CONFIG_NUMA))
+				show_numa_info(m, v, counters);
+
 			seq_putc(m, '\n');
 		}
 		spin_unlock(&vn->busy.lock);
@@ -5042,19 +5054,14 @@ static int vmalloc_info_show(struct seq_file *m, void *p)
 	 * As a final step, dump "unpurged" areas.
 	 */
 	show_purge_info(m);
+	if (IS_ENABLED(CONFIG_NUMA))
+		kfree(counters);
 	return 0;
 }
 
 static int __init proc_vmalloc_init(void)
 {
-	void *priv_data = NULL;
-
-	if (IS_ENABLED(CONFIG_NUMA))
-		priv_data = kmalloc(nr_node_ids * sizeof(unsigned int), GFP_KERNEL);
-
-	proc_create_single_data("vmallocinfo",
-		0400, NULL, vmalloc_info_show, priv_data);
-
+	proc_create_single("vmallocinfo", 0400, NULL, vmalloc_info_show);
 	return 0;
 }
 module_init(proc_vmalloc_init);