[PATCH v5] mm/vmalloc: fix data race in show_numa_info()

Jeongjun Park
2025-05-08T16:08:28Z

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.

Fixes: a47a126ad5ea ("vmallocinfo: add NUMA information")
Suggested-by: Eric Dumazet <edumazet@google.com>
Suggested-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
v5: Change heap to be allocated only when CONFIG_NUMA is enabled
- Link to v4: https://lore.kernel.org/all/20250508065558.149091-1-aha310510@gmail.com/
v4: Change the way counters array heap is allocated, per Andrew Morton's suggestion.
And fix it to call smp_rmb() in the correct location.
- Link to v3: https://lore.kernel.org/all/20250507142552.9446-1-aha310510@gmail.com/
v3: Following Uladzislau Rezki's suggestion, we check v->flags beforehand
to avoid printing uninitialized members of vm_struct.
- Link to v2: https://lore.kernel.org/all/20250506082520.84153-1-aha310510@gmail.com/
v2: Refactoring some functions and fix patch as per Eric Dumazet suggestion
- Link to v1: https://lore.kernel.org/all/20250505171948.24410-1-aha310510@gmail.com/
---
mm/vmalloc.c | 62 ++++++++++++++++++++++++++++------------------------
1 file changed, 34 insertions(+), 28 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 3ed720a787ec..866f18766dfc 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3100,7 +3100,7 @@ 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;
@@ -4914,28 +4914,29 @@ 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)
@@ -4962,8 +4963,12 @@ 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 = NULL;
int i;

+ if (IS_ENABLED(CONFIG_NUMA))
+ counters = kmalloc(nr_node_ids * sizeof(unsigned int), GFP_KERNEL);
+
for (i = 0; i < nr_vmap_nodes; i++) {
vn = &vmap_nodes[i];

@@ -4979,6 +4984,11 @@ 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);
@@ -5013,7 +5023,9 @@ 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 (counters)
+ show_numa_info(m, v, counters);
+
seq_putc(m, '\n');
}
spin_unlock(&vn->busy.lock);
@@ -5023,19 +5035,13 @@ static int vmalloc_info_show(struct seq_file *m, void *p)
* As a final step, dump "unpurged" areas.
*/
show_purge_info(m);
+ 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);
--