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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rp5oC-00000001FQ5-46kw; Tue, 26 Mar 2024 12:21:41 +0000 Date: Tue, 26 Mar 2024 12:21:40 +0000 From: Matthew Wilcox To: Zhaoyang Huang Cc: =?utf-8?B?6buE5pyd6ZizIChaaGFveWFuZyBIdWFuZyk=?= , Andrew Morton , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , =?utf-8?B?5bq357qq5ruoIChTdGV2ZSBLYW5nKQ==?= Subject: Re: summarize all information again at bottom//reply: reply: [PATCH] mm: fix a race scenario in folio_isolate_lru Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Stat-Signature: amfywwr1umkf94tzn1u79xqyqmhcheoo X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 3F08B180019 X-HE-Tag: 1711455706-566952 X-HE-Meta: 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 JGtNbRig Qn0D0oavQWSr7te6M+EoyayW3eQXfaVYZkKGF6ft1N4GIV1D5+1m1UicHsKcR8Y35o7B9h9GC12zQroelPqg2Ba1vsIbHjQ0BXMfUBB2/pMnLepbnvxGUkZ/KVU6m0hFmhymtCr/BsMzlUWB6gNesgZ/aGFvbk/bG57sbzv+KAP39r1LVpGaS4qS2vzKP8fTjVdtaqCrmbYukD6aAROZrRN3AT+Oz/WI01p+b X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 26, 2024 at 05:06:55PM +0800, Zhaoyang Huang wrote: > 1. Thread_readahead remove the folio from page cache and drop 2 refcnt > by readahead_folio & filemap_remove_folio(get rid of the folios which > failed to launch IO during readahead) > refcnt == 0, PG_lru == true, PG_lock == true > read_pages > ... > folio = readahead_folio > > ********For the folio which can not launch IO, we should NOT drop > refcnt here??? replaced by __readahead_folio???********** > folio_get > filemap_remove_folio(folio) > folio_unlock > > folio_put Ignoring any other thread, you're basically saying that there's a refcount imbalance here. Which means we'd hit an assert (that folio refcount went below zero) in the normal case where another thread wasn't simultaneously trying to do anything.