linux-kernel - Re: [PATCH 1/1] mm: protect xa split stuff under lruvec->lru

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Date: Fri, 12 Apr 2024 13:24:36 +0100
From: Matthew Wilcox <willy@...radead.org>
To: "zhaoyang.huang" <zhaoyang.huang@...soc.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Alex Shi <alexs@...nel.org>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Zhaoyang Huang <huangzhaoyang@...il.com>, steve.kang@...soc.com
Subject: Re: [PATCH 1/1] mm: protect xa split stuff under lruvec->lru_lock
 during migration

On Fri, Apr 12, 2024 at 02:43:53PM +0800, zhaoyang.huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> 
> Livelock in [1] is reported multitimes since v515, where the zero-ref
> folio is repeatly found on the page cache by find_get_entry. A possible
> timing sequence is proposed in [2], which can be described briefly as

I have no patience for going through another one of your "analyses".

1. Can you reproduce this bug without this patch?
2. Does the reproducer stop working after this patch?

Otherwise I'm not interested.  Sorry.  You burnt all my good will.

> the lockless xarray operation could get harmed by an illegal folio
> remaining on the slot[offset]. This commit would like to protect
> the xa split stuff(folio_ref_freeze and __split_huge_page) under
> lruvec->lock to remove the race window.