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(was Re: [PATCH v3 6/7] mm/swap, shmem: use unified swapin helper for shmem) In-Reply-To: <20240129175423.1987-7-ryncsn@gmail.com> (Kairui Song's message of "Tue, 30 Jan 2024 01:54:21 +0800") References: <20240129175423.1987-1-ryncsn@gmail.com> <20240129175423.1987-7-ryncsn@gmail.com> Date: Wed, 31 Jan 2024 10:51:38 +0800 Message-ID: <87bk92gqpx.fsf_-_@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 28F924000A X-Stat-Signature: qn938djshj9nfgsmkfp67qkozkknhdoa X-HE-Tag: 1706669619-928430 X-HE-Meta: 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 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: Hi, Minchan, When I review the patchset from Kairui, I checked the code to skip swap cache in do_swap_page() for swap device with SWP_SYNCHRONOUS_IO. Is the following race possible? Where a page is swapped out to a swap device with SWP_SYNCHRONOUS_IO and the swap count is 1. Then 2 threads of the process runs on CPU0 and CPU1 as below. CPU0 is running do_swap_page(). CPU0 CPU1 ---- ---- swap_cache_get_folio() check sync io and swap count alloc folio swap_readpage() folio_lock_or_retry() swap in the swap entry write page swap out to same swap entry pte_offset_map_lock() check pte_same() swap_free() <-- new content lost! set_pte_at() <-- stale page! folio_unlock() pte_unmap_unlock() Do I miss anything? -- Best Regards, Huang, Ying