linux-kernel - Re: [PATCH] mm: fix hard lockup in __split_huge

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Date: Tue, 18 Jun 2024 11:42:17 +0800
From: Zhaoyang Huang <huangzhaoyang@...il.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: "zhaoyang.huang" <zhaoyang.huang@...soc.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, steve.kang@...soc.com
Subject: Re: [PATCH] mm: fix hard lockup in __split_huge_page

On Tue, Jun 18, 2024 at 11:31 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Tue, Jun 18, 2024 at 11:27:12AM +0800, Zhaoyang Huang wrote:
> > On Tue, Jun 18, 2024 at 11:19 AM Matthew Wilcox <willy@...radead.org> wrote:
> > >
> > > On Tue, Jun 18, 2024 at 10:09:26AM +0800, zhaoyang.huang wrote:
> > > > Hard lockup[2] is reported which should be caused by recursive
> > > > lock contention of lruvec->lru_lock[1] within __split_huge_page.
> > > >
> > > > [1]
> > > > static void __split_huge_page(struct page *page, struct list_head *list,
> > > >                 pgoff_t end, unsigned int new_order)
> > > > {
> > > >         /* lock lru list/PageCompound, ref frozen by page_ref_freeze */
> > > > //1st lock here
> > > >         lruvec = folio_lruvec_lock(folio);
> > > >
> > > >         for (i = nr - new_nr; i >= new_nr; i -= new_nr) {
> > > >                 __split_huge_page_tail(folio, i, lruvec, list, new_order);
> > > >                 /* Some pages can be beyond EOF: drop them from page cache */
> > > >                 if (head[i].index >= end) {
> > > >                         folio_put(tail);
> > > >                             __page_cache_release
> > > > //2nd lock here
> > > >                                folio_lruvec_relock_irqsave
> > >
> > > Why doesn't lockdep catch this?
> > It is reported by a regression test of the fix patch which aims at the
> > find_get_entry livelock issue as below. I don't know the details of
> > the kernel configuration.
> >
> > https://lore.kernel.org/linux-mm/5f989315-e380-46aa-80d1-ce8608889e5f@marcinwanat.pl/
>
> Go away.
ok, you are the boss anyway. But this series of call chain does have
the risk of deadlock, right? Besides, the livelock issue which is
caused by zero ref-count folio within find_get_entry is kept being
reported by different users.

https://lore.kernel.org/linux-mm/CALOAHbC8NM7R-pKvPW6m4fnn_8BQZuPjJrNZaEN=sg67Gp+NGQ@mail.gmail.com/