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From: Miklos Szeredi <miklos@szeredi.hu>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Amir Goldstein <amir73il@gmail.com>,
	Al Viro <viro@zeniv.linux.org.uk>, Linux MM <linux-mm@kvack.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	overlayfs <linux-unionfs@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Matthew Wilcox <willy@infradead.org>,
	Colin Walters <walters@verbum.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	syzbot <syzbot+d6ec23007e951dadf3de@syzkaller.appspotmail.com>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>
Subject: Re: [PATCH v4 1/2] hugetlb: use f_mode & FMODE_HUGETLBFS to identify hugetlbfs files
Date: Tue, 16 Jun 2020 11:01:13 +0200	[thread overview]
Message-ID: <CAJfpeguTnVOTq4u_E=wDPcJ7vJE_jsAOi_ztm0Pt=X1qtC8ObA@mail.gmail.com> (raw)
In-Reply-To: <80f869aa-810d-ef6c-8888-b46cee135907@oracle.com>

On Tue, Jun 16, 2020 at 1:45 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 6/15/20 12:53 AM, Miklos Szeredi wrote:
> > On Sat, Jun 13, 2020 at 9:12 PM Mike Kravetz <mike.kravetz@oracle.com> wrote:
> >> On 6/12/20 11:53 PM, Amir Goldstein wrote:
> >>>
> >>> The simplest thing for you to do in order to shush syzbot is what procfs does:
> >>>         /*
> >>>          * procfs isn't actually a stacking filesystem; however, there is
> >>>          * too much magic going on inside it to permit stacking things on
> >>>          * top of it
> >>>          */
> >>>         s->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;
> >>>
> >>> Currently, the only in-tree stacking fs are overlayfs and ecryptfs, but there
> >>> are some out of tree implementations as well (shiftfs).
> >>> So you may only take that option if you do not care about the combination
> >>> of hugetlbfs with any of the above.
> >>>
> >>> overlayfs support of mmap is not as good as one might hope.
> >>> overlayfs.rst says:
> >>> "If a file residing on a lower layer is opened for read-only and then
> >>>  memory mapped with MAP_SHARED, then subsequent changes to
> >>>  the file are not reflected in the memory mapping."
> >>>
> >>> So if I were you, I wouldn't go trying to fix overlayfs-huguetlb interop...
> >>
> >> Thanks again,
> >>
> >> I'll look at something as simple as s_stack_depth.
> >
> > Agree.
>
> Apologies again for in the incorrect information about writing to lower
> filesystem.
>
> Stacking ecryptfs on hugetlbfs does not work either.  Here is what happens
> when trying to create a new file.
>
> [ 1188.863425] ecryptfs_write_metadata_to_contents: Error attempting to write header information to lower file; rc = [-22]
> [ 1188.865469] ecryptfs_write_metadata: Error writing metadata out to lower file; rc = [-22]
> [ 1188.867022] Error writing headers; rc = [-22]
>
> I like Amir's idea of just setting s_stack_depth in hugetlbfs to prevent
> stacking.
>
> From 0fbed66b37c18919ea7edd47b113c97644f49362 Mon Sep 17 00:00:00 2001
> From: Mike Kravetz <mike.kravetz@oracle.com>
> Date: Mon, 15 Jun 2020 14:37:52 -0700
> Subject: [PATCH] hugetlbfs: prevent filesystem stacking of hugetlbfs
>
> syzbot found issues with having hugetlbfs on a union/overlay as reported
> in [1].  Due to the limitations (no write) and special functionality of
> hugetlbfs, it does not work well in filesystem stacking.  There are no
> know use cases for hugetlbfs stacking.  Rather than making modifications
> to get hugetlbfs working in such environments, simply prevent stacking.
>
> [1] https://lore.kernel.org/linux-mm/000000000000b4684e05a2968ca6@google.com/
>
> Reported-by: syzbot+d6ec23007e951dadf3de@syzkaller.appspotmail.com
> Suggested-by: Amir Goldstein <amir73il@gmail.com>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>

Acked-by: Miklos Szeredi <mszeredi@redhat.com>

Thanks,
Miklos

  reply	other threads:[~2020-06-16  9:01 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-12  0:46 Mike Kravetz
2020-06-12  0:46 ` [PATCH v4 2/2] ovl: call underlying get_unmapped_area() routine. propogate FMODE_HUGETLBFS Mike Kravetz
2020-06-14 12:50   ` Amir Goldstein
2020-06-12  1:53 ` [PATCH v4 1/2] hugetlb: use f_mode & FMODE_HUGETLBFS to identify hugetlbfs files Matthew Wilcox
2020-06-12  1:58 ` Al Viro
2020-06-12 21:51   ` Mike Kravetz
2020-06-13  6:53     ` Amir Goldstein
2020-06-13 14:38       ` Matthew Wilcox
2020-06-13 19:12       ` Mike Kravetz
2020-06-15  7:53         ` Miklos Szeredi
2020-06-15 10:05           ` Amir Goldstein
2020-06-15 13:01             ` Miklos Szeredi
2020-06-15 23:45           ` Mike Kravetz
2020-06-16  9:01             ` Miklos Szeredi [this message]
2020-06-15  8:24       ` Miklos Szeredi
2020-06-15 17:48         ` Mike Kravetz
2020-06-12  6:28 ` [RFC PATCH] hugetlb: hugetlbfs_file_operations can be static kernel test robot

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