Re: [PATCH v4 1/2] hugetlb: use f_mode & FMODE_HUGETLBFS to identify hugetlbfs files

[Mike Kravetz]

On 6/15/20 1:24 AM, Miklos Szeredi wrote:
> On Sat, Jun 13, 2020 at 8:53 AM Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> 
>>> I also looked at normal filesystem lower and hugetlbfs upper.  Yes, overlayfs
>>> allows this.  This is somewhat 'interesting' as write() is not supported in
>>> hugetlbfs.  Writing to files in the overlay actually ended up writing to
>>> files in the lower filesystem.  That seems wrong, but overlayfs is new to me.
> 
> Yes, this very definitely should not happen.
> 
>> I am not sure how that happened, but I think that ovl_open_realfile()
>> needs to fixup f_mode flags FMODE_CAN_WRITE | FMODE_CAN_READ
>> after open_with_fake_path().
> 
> Okay, but how did the write actually get to the lower layer?
> 
> I failed to reproduce this.  Mike, how did you trigger this?

My apologies!!!

I reviewed my testing and found that it was incorrectly writing to the
lower filesystem.  Writing to any file in the union will fail.
-- 
Mike Kravetz