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Date: Thu, 28 Mar 2024 03:18:27 +0000
From: Matthew Wilcox <willy@infradead.org>
To: Zhaoyang Huang <huangzhaoyang@gmail.com>
Cc: =?utf-8?B?6buE5pyd6ZizIChaaGFveWFuZyBIdWFuZyk=?= <zhaoyang.huang@unisoc.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	=?utf-8?B?5bq357qq5ruoIChTdGV2ZSBLYW5nKQ==?= <Steve.Kang@unisoc.com>
Subject: Re: summarize all information again at bottom//reply: reply: [PATCH]
 mm: fix a race scenario in folio_isolate_lru
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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.