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

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Date:   Mon, 19 Jul 2021 13:59:20 +0200
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     Matthew Wilcox <willy@...radead.org>,
        Miaohe Lin <linmiaohe@...wei.com>
Cc:     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 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.com
> 
> > 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?

-- 
Oleksandr Natalenko (post-factum)