Re: [PATCH 6.3.y] mm/hugetlb: revert use of page_cache_next_miss()

[Greg KH]

On Tue, Jun 06, 2023 at 11:13:05AM -0700, Sidhartha Kumar wrote:
> On 6/6/23 10:38 AM, Greg KH wrote:
> > On Tue, Jun 06, 2023 at 10:20:22AM -0700, Sidhartha Kumar wrote:
> > > As reported by Ackerley[1], the use of page_cache_next_miss() in
> > > hugetlbfs_fallocate() introduces a bug where a second fallocate() call to
> > > same offset fails with -EEXIST. Revert this change and go back to the
> > > previous method of using get from the page cache and then dropping the
> > > reference on success.
> > > 
> > > hugetlbfs_pagecache_present() was also refactored to use
> > > page_cache_next_miss(), revert the usage there as well.
> > > 
> > > User visible impacts include hugetlb fallocate incorrectly returning
> > > EEXIST if pages are already present in the file. In addition, hugetlb
> > > pages will not be included in core dumps if they need to be brought in via
> > > GUP. userfaultfd UFFDIO_COPY also uses this code and will not notice pages
> > > already present in the cache. It may try to allocate a new page and
> > > potentially return ENOMEM as opposed to EEXIST.
> > > 
> > > Fixes: d0ce0e47b323 ("mm/hugetlb: convert hugetlb fault paths to use alloc_hugetlb_folio()")
> > > Cc: <stable@xxxxxxxxxxxxxxx> #v6.3
> > > Reported-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
> > > Signed-off-by: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
> > > Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> > > 
> > > [1] https://lore.kernel.org/linux-mm/cover.1683069252.git.ackerleytng@xxxxxxxxxx/
> > > ---
> > > 
> > > This revert is the safest way to fix 6.3. The upstream fix will either
> > > fix page_cache_next_miss() itself or use Ackerley's patch to introduce a
> > > new function to check if a page is present in the page cache. Both
> > > directions are currently under review so we can use this safe and simple
> > > fix for 6.3
> > 
> > Is there any specific reason why we don't just wait for the fix for
> > Linus's tree before applying this one, or applying the real fix instead?
> 
> I missed Andrew's message stating he would prefer the real fix[1].
> 
> Sorry for the noise,
> Sidhartha Kumar
> 
> [1] https://lore.kernel.org/lkml/20230603022209.GA114055@monkey/T/#mea6c8a015dbea5f9c2be88b9791996f4be6c2de8

Great, is that going to Linus's tree soon?

thanks,

greg k-h