On Tue, Jun 16, 2020 at 1:45 AM Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote: > > On 6/15/20 12:53 AM, Miklos Szeredi wrote: > > On Sat, Jun 13, 2020 at 9:12 PM Mike Kravetz <mike.kravetz@xxxxxxxxxx> 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@xxxxxxxxxx> > 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@xxxxxxxxxx/ > > Reported-by: syzbot+d6ec23007e951dadf3de@xxxxxxxxxxxxxxxxxxxxxxxxx > Suggested-by: Amir Goldstein <amir73il@xxxxxxxxx> > Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Acked-by: Miklos Szeredi <mszeredi@xxxxxxxxxx> Thanks, Miklos
