mainline inclusion
from mainline-v5.15
commit d144bf62
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I58GJ0
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d144bf6205342a4b5fed5d204ae18849a4de741b

--------------------------------

A successful shmem_fallocate() guarantees that the extent has been
reserved, even beyond i_size when the FALLOC_FL_KEEP_SIZE flag was used.
But that guarantee is broken by shmem_unused_huge_shrink()'s attempts to
split huge pages and free their excess beyond i_size; and by other uses of
split_huge_page() near i_size.

It's sad to add a shmem inode field just for this, but I did not find a
better way to keep the guarantee.  A flag to say KEEP_SIZE has been used
would be cheaper, but I'm averse to unclearable flags.  The fallocend
field is not perfect either (many disjoint ranges might be fallocated),
but good enough; and gains another use later on.

Link: https://lkml.kernel.org/r/ca9a146-3a59-6cd3-7f28-e9a044bb1052@google.com
Fixes: 779750d2 ("shmem: split huge pages beyond i_size under memory pressure")
Signed-off-by: NHugh Dickins <hughd@google.com>
Reviewed-by: NYang Shi <shy828301@gmail.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NChen Wandun <chenwandun@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>