Re: [PATCH linux-next] Fix shmem huge page failed to set F_SEAL_WRITE attribute problem

[CGEL <cgel.zte@gmail.com>]

O Tue, Feb 15, 2022 at 02:12:36PM -0800, Andrew Morton wrote:
> On Tue, 15 Feb 2022 07:37:43 +0000 cgel.zte@gmail.com wrote:
> 
> > From: wangyong <wang.yong12@zte.com.cn>
> > 
> > After enabling tmpfs filesystem to support transparent hugepage with the
> > following command:
> >  echo always > /sys/kernel/mm/transparent_hugepage/shmem_enabled
> > The docker program adds F_SEAL_WRITE through the following command will
> > prompt EBUSY.
> >  fcntl(5, F_ADD_SEALS, F_SEAL_WRITE)=-1.
> > 
> > It is found that in memfd_wait_for_pins function, the page_count of
> > hugepage is 512 and page_mapcount is 0, which does not meet the
> > conditions:
> >  page_count(page) - page_mapcount(page) != 1.
> > But the page is not busy at this time, therefore, the page_order of
> > hugepage should be taken into account in the calculation.
> 
> What are the real-world runtime effects of this?
>
The problem I encounter is that the "docker-runc run busybox" command
fails, and then the container cannot be started. The following alarm is
prompted:
[pid  1412] fcntl(5, F_ADD_SEALS,F_SEAL_SEAL|F_SEAL_SHRINK|F_SEAL_GROW|F_SEAL_WRITE) = -1 EBUSY (Device or resource busy)
[pid  1412] close(5)                    = 0
[pid  1412] write(2, "nsenter: could not ensure we are"..., 74) = 74
...
[pid  1491] write(3, "\33[31mERRO\33[0m[0005] container_li"..., 166) = 166
[pid  1491] write(2, "container_linux.go:299: starting"..., 144container_linux.go:299: starting container process caused
"process_linux.go:245: running exec setns process for init caused \"exit statu" ) = 144

I'm not sure how this will affect other situations.
> Do we think that this fix (or one similar to it) should be backported
> into -stable kernels?
> 
> If "yes" then Mike's 5d752600a8c373 ("mm: restructure memfd code") will
> get in the way because it moved lots of code around.
> 
Yes, 4.14 does not have this patch, but 4.19 does.
In addition, Kirill A. Shutemov's 800d8c63b2e989c2e349632d1648119bf5862f01 
(shmem: add huge pages support) is not included in 4.4, but it is available in 4.14.

> But then, that's four years old and perhaps that's far enough back in
> time.

Thanks.