Re: [PATCH 6.15.y] mm/vmalloc: fix data race in show_numa_info()

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Jul 03, 2025 at 12:33:12AM +0900, Jeongjun Park wrote:
> commit 5c5f0468d172ddec2e333d738d2a1f85402cf0bc upstream.
> 
> 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: 8e1d743 ("mm: vmalloc: support multiple nodes in vmallocinfo")

Why did you change this line?

> 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>
> ---
>  mm/vmalloc.c | 63 +++++++++++++++++++++++++++++-----------------------
>  1 file changed, 35 insertions(+), 28 deletions(-)

Please document what you changed from the original version, as this does
not match what is in Linus's tree.

thanks,

greg k-h