linux-kernel - Re: [PATCH 6.12.y] mm/vmalloc: fix data race in show_numa

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Message-ID: <2025070315-breezy-bogged-75f3@gregkh>
Date: Thu, 3 Jul 2025 12:06:32 +0200
From: Greg KH <greg@...ah.com>
To: Jeongjun Park <aha310510@...il.com>
Cc: stable@...r.kernel.org, urezki@...il.com, akpm@...ux-foundation.org,
	edumazet@...gle.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6.12.y] mm/vmalloc: fix data race in show_numa_info()

On Thu, Jul 03, 2025 at 12:34:28AM +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")

Same comments on the 6.15 version, why change this line?

thanks,

greg k-h