On Mon, Jul 19, 2021 at 02:12:15PM +0200, Oleksandr Natalenko wrote:

On pondělí 19. července 2021 14:08:37 CEST Miaohe Lin wrote:

quoted

On 2021/7/19 19:59, Oleksandr Natalenko wrote:

quoted

On pondělí 19. července 2021 13:50:07 CEST Miaohe Lin wrote:

quoted

On 2021/7/19 19:22, Matthew Wilcox wrote:

quoted

On Mon, Jul 19, 2021 at 07:12:58PM +0800, Miaohe Lin wrote:

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When in the commit 2799e77529c2a, we're using the percpu_ref to
serialize
against concurrent swapoff, i.e. there's percpu_ref inside
get_swap_device() instead of rcu_read_lock(). Please see commit
63d8620ecf93 ("mm/swapfile: use percpu_ref to serialize against
concurrent swapoff") for detail.

Oh, so this is a backport problem.  2799e77529c2 was backported without
its prerequisite 63d8620ecf93.  Greg, probably best to just drop

Yes, they're posted as a patch set:

https://lkml.kernel.org/r/20210426123316.806267-1-linmiaohe@huawei.com

quoted

2799e77529c2 from all stable trees; the race described is not very
important (swapoff vs reading a page back from that swap device).
.

The swapoff races with reading a page back from that swap device should
be
really uncommon as most users only do swapoff when the system is going to
shutdown.

Sorry for the trouble!

git log --oneline v5.13..v5.13.3 --author="Miaohe Lin"
11ebc09e50dc mm/zswap.c: fix two bugs in zswap_writeback_entry()
95d192da198d mm/z3fold: use release_z3fold_page_locked() to release locked
z3fold page
ccb7848e2344 mm/z3fold: fix potential memory leak in z3fold_destroy_pool()
9f7229c901c1 mm/huge_memory.c: don't discard hugepage if other processes
are mapping it
f13259175e4f mm/huge_memory.c: add missing read-only THP checking in
transparent_hugepage_enabled()
afafd371e7de mm/huge_memory.c: remove dedicated macro
HPAGE_CACHE_INDEX_MASK a533a21b692f mm/shmem: fix shmem_swapin() race
with swapoff
c3b39134bbd0 swap: fix do_swap_page() race with swapoff

Do you suggest reverting "mm/shmem: fix shmem_swapin() race with swapoff"
as well?

This patch also rely on its prerequisite 63d8620ecf93. I think we should
either revert any commit in this series or just backport the entire series.

Then why not just pick up 2 more patches instead of dropping 2 patches. Greg, 
could you please make sure the whole series from [1] gets pulled?

Because none of these patches should have been backported in the first
place.  It's just not worth the destabilisation.