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

Uladzislau Rezki
2025-05-08T16:13:50Z

On Fri, May 09, 2025 at 01:07:59AM +0900, Jeongjun Park wrote:
> 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);
> +
Let's execute it for NUMA only.

> 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);
Let's execute it for NUMA only.

> 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);
> --

You are so fast :)

--
Uladzislau Rezki