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

[Jeongjun Park <aha310510@gmail.com>]

Greg KH <gregkh@linuxfoundation.org> wrote:
>
> 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?

Oops, I accidentally imported the commit message from GitHub, so this
commit hash was shortened to 7 digits. I'll fix it right away and send
v2 patch.

>
> > 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

Regards,

Jeongjun Park