linux-kernel - Re: summarize all information again at bottom//reply: reply: [PATCH] mm: fix a race scenario in folio_isolate

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Date: Thu, 28 Mar 2024 03:18:27 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Zhaoyang Huang <huangzhaoyang@...il.com>
Cc: 黄朝阳 (Zhaoyang Huang) <zhaoyang.huang@...soc.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	康纪滨 (Steve Kang) <Steve.Kang@...soc.com>
Subject: Re: summarize all information again at bottom//reply: reply: [PATCH]
 mm: fix a race scenario in folio_isolate_lru

On Thu, Mar 28, 2024 at 09:27:31AM +0800, Zhaoyang Huang wrote:
> ok, I missed the refcnt from alloc_pages. However, I still think it is
> a bug to call readahead_folio in read_pages as the refcnt obtained by
> alloc_pages should be its final guard which is paired to the one which
> checked in shrink_folio_list->__remove_mapping->folio_ref_freeze(2)(this
> 2 represent alloc_pages & page cache). If we removed this one without

__remove_mapping()  requires that the caller holds the folio locked.
Since the readahead code unlocks the folio, __remove_mapping() cannot
be run because the caller of __remove_mapping() will wait for the folio
lock.