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b=RbdlsP83pI0g/GUuM6VbZ/P7fr3ctS+PR6qMg7VJjK38uiDEInGcgR8axZzFGyzch Xu8ztux3zdWT/cyx43bEg029AF65TcMp6iUv4cfkEpEGcwA5TdhzIlkR1JM5IBiYkS scMq6PvraM+qnz0paWREPYrC4vjw9IkmsHcfuec+D98dS+YOkzzEjLYhkjY44jJiRf 0rHtxNgZg6QQ+IpqUuHkD5F1Po5gI9bi5/DwYKYslq1ccb1h+m0ry7Ptpvr5G4QivF jNGNIs/fyfOoWObaQePwocAIqdd/Pi9bPa3VTfoe3KnH6uMFPOkKoCGDR9+NqE/nuK AVGed6pJRYBjQ== Message-ID: <3edbd664-a6f9-4344-8a6c-6e3feebf728a@kernel.org> Date: Tue, 27 Oct 2026 10:53:27 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 06/16] mm/shmem: hold off eviction in shmem_writeout() To: Kiryl Shutsemau Cc: Andrew Morton , Gregory Price , Zi Yan , Joshua Hahn , Rakie Kim , Ying Huang , Johannes Weiner , Vladimir Davydov , Michal Hocko , Hugh Dickins , Baolin Wang , Lukas Czerner , Carlos Maiolino , Christian Brauner , Jan Kara , Daniel Verkamp , Jeff Xu , Muchun Song , Oscar Salvador , David Stevens , "Matthew Wilcox (Oracle)" , William Kucharski , Chris Li , Kairui Song , Nhat Pham , Miaohe Lin , Naoya Horiguchi , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Josef Bacik , stable@vger.kernel.org References: <20261026-fixes_shmem-v1-0-703206d5fa0c@kernel.org> <20261026-fixes_shmem-v1-6-703206d5fa0c@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: E4F3C80007 X-Stat-Signature: jq9jkk3qqmi3yq41jtdugnri76dbg3p1 X-Rspam-User: X-Spam-Status: No, score=-12.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793096002-62180 X-HE-Meta: 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 AGHVBV4v 7fAH7zjXuHeTOzq3Z98RJYZHUrTsRdUK3PpeWCCJme3inU3TWSyi47762QP5/RJWuLkZqhfeZ2rWzXG7s1dmwTbkC1eLy64PyHmtPCQtMYdKGYMVHRiLXl3Kfm030XFgzLXVBpvHx+S0kjSd6+yijSpUItZKfKcNWQTFH85l0DxwPSPTtXJXR8XQQ1T0SfwqG0InzVFbyC+sq7zhrc12pkqspGV4GzUKGr6XgZe+8NubhcbWnGedqnM3APyBqk85eZ/tLhrHAcUg8L2CXigEiFj2a8b2k40WliKgEgBzBCfCenwLqvl0ecsrPF11DzhaQj9MdZdQN7xIdgyGEKLf3ZMv95Dp5YRqf0Bhlbjwud1kN6+CHwW2H7iRjiXhFnVbQGpcskGhI5h2y1bT0HLDs1ldEFwHXmxYBdclWbYic9LU88x4Hp6MA4FGhenjVlRlfDzef9R1Q+3XCpGvD8lPNLJ0Ppw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/26/26 17:13, Kiryl Shutsemau wrote: > On Mon, Oct 26, 2026 at 10:40:39AM +0100, David Hildenbrand (Arm) wrote: >> From: Josef Bacik >> >> Once shmem_writeout() has moved the folio from the page cache to the >> swap cache, the folio lock no longer keeps the inode alive: truncation >> and eviction find a swap entry, free it and do not wait for anybody. >> That did not matter as long as swap_writeout() was the last thing the >> function did. But since it puts the folio back when swap_writeout() >> returns AOP_WRITEPAGE_ACTIVATE, it uses the mapping and the inode >> afterwards: >> >> reclaim last close of an unlinked file >> shmem_writeout() >> shmem_delete_from_page_cache() >> swap_writeout() >> zswap_store() fails shmem_evict_inode() >> writeback is disabled shmem_truncate_range() >> return AOP_WRITEPAGE_ACTIVATE shmem_free_swap() >> destroy_inode() >> ... RCU grace period, freed >> shmem_add_to_page_cache(mapping) >> xas_lock_irq() <- use after free >> >> swap_writeout() behaves that way if zswap is enabled, cannot take the >> folio and the memcg or one of its ancestors has memory.zswap.writeback >> set to 0. >> >> shmem_unuse() already added infrastructure to deal with that. >> Reuse info->stop_eviction to protect the inode during writeout. Increment >> it before removing the folio from the page cache, and decrement it after >> swap_writeout() and any attempted reinsertion and inode accounting. >> In shmem_evict_inode(), wait for the counter to reach zero even if >> swapoff has already removed the inode from the swap list. Add some helpers >> to make the code easier to digest. >> >> Fix generated by an LLM and sent by Josef Bacik in private. >> >> Fixes: 6344a6d9ce13 ("mm/shmem: writeout free swap if swap_writeout() reactivates") >> Cc: stable@vger.kernel.org >> Signed-off-by: Josef Bacik >> [ david: code cleanups; improve description ] >> Signed-off-by: David Hildenbrand (Arm) > > ->stop_eviction is ugly, but, oh, well... yeah, I was not particularly happy to learn that this exists ... Thanks everybody for the review! -- Cheers, David