+ hugetlbfs-prevent-filesystem-stacking-of-hugetlbfs.patch added to -mm tree

+ hugetlbfs-prevent-filesystem-stacking-of-hugetlbfs.patch added to -mm tree

[akpm]

The patch titled
     Subject: hugetlbfs: prevent filesystem stacking of hugetlbfs
has been added to the -mm tree.  Its filename is
     hugetlbfs-prevent-filesystem-stacking-of-hugetlbfs.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/hugetlbfs-prevent-filesystem-stacking-of-hugetlbfs.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/hugetlbfs-prevent-filesystem-stacking-of-hugetlbfs.patch

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------------------------------------------------------
From: Mike Kravetz <mike.kravetz@oracle.com>
Subject: 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/

Link: http://lkml.kernel.org/r/80f869aa-810d-ef6c-8888-b46cee135907@oracle.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reported-by: syzbot+d6ec23007e951dadf3de@syzkaller.appspotmail.com
Suggested-by: Amir Goldstein <amir73il@gmail.com>
Acked-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Colin Walters <walters@verbum.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/hugetlbfs/inode.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/fs/hugetlbfs/inode.c~hugetlbfs-prevent-filesystem-stacking-of-hugetlbfs
+++ a/fs/hugetlbfs/inode.c
@@ -1364,6 +1364,12 @@ hugetlbfs_fill_super(struct super_block
 	sb->s_magic = HUGETLBFS_MAGIC;
 	sb->s_op = &hugetlbfs_ops;
 	sb->s_time_gran = 1;
+
+	/*
+	 * Due to the special and limited functionality of hugetlbfs, it does
+	 * not work well as a stacking filesystem.
+	 */
+	sb->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;
 	sb->s_root = d_make_root(hugetlbfs_get_root(sb, ctx));
 	if (!sb->s_root)
 		goto out_free;
_

Patches currently in -mm which might be from mike.kravetz@oracle.com are

hugetlbfs-prevent-filesystem-stacking-of-hugetlbfs.patch