linux-kernel - Re: linux-5.13.2: warning from kernel/rcu/tree

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Date:   Mon, 19 Jul 2021 14:23:55 +0200
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Miaohe Lin <linmiaohe@...wei.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Zhouyi Zhou <zhouzhouyi@...il.com>, paulmck@...nel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org, Chris Clayton <chris2553@...glemail.com>,
        Chris Rankin <rankincj@...il.com>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        rcu <rcu@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        "Huang, Ying" <ying.huang@...el.com>, gregkh@...uxfoundation.org
Subject: Re: linux-5.13.2: warning from kernel/rcu/tree_plugin.h:359

On pondělí 19. července 2021 14:16:04 CEST Matthew Wilcox wrote:
> 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:
> > > On 2021/7/19 19:59, Oleksandr Natalenko wrote:
> > > > On pondělí 19. července 2021 13:50:07 CEST Miaohe Lin wrote:
> > > >> On 2021/7/19 19:22, Matthew Wilcox wrote:
> > > >>> On Mon, Jul 19, 2021 at 07:12:58PM +0800, Miaohe Lin wrote:
> > > >>>> 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.co
> > > >> m
> > > >> 
> > > >>> 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.

What about the rest then?

git log --oneline v5.13..v5.13.3 -- mm/ | wc -l
18

Those look to be fixes, these ones too.

-- 
Oleksandr Natalenko (post-factum)