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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b="ixV/2IIx"; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A01A0606A329; Fri, 6 Nov 2026 20:58:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=ixV/2IIx Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5B98F1F0089F; Fri, 6 Nov 2026 20:58:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793998735; bh=ts4CDaprMowxWHfO4PT+4syTNjSDN3DCqaoaeja+YDo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ixV/2IIxtyoMfQ4XY/DicKZo88+pkjPXzsU02Qi9R0BXW9GY1+LyVbI+Y3PTz6PHV OWvf4Jg3HGprZ3yx8gHHu3OUatkGnGjgSx4n0rChHDspyH70WZyHUwr/pQHFs0QYh3 zxXIxhqGqN8p7QcujIGzCQ4e0RKFj43VPenPPUvqMNpXvWWTyX9XQChUrudvaxHonT k2S4YTXioJCyF+QuLEVcI7pmC+e3VhXrFqj8/IFcna4/pitkTsupLtJCQziB7/UlLZ 9YNUC8h5RCNSAlCKwSWcFftx7GctOKkRQ11A7i/APwnObeXr/EwG8isa2T4+wu4Kvt LPrDkclzmTq6w== Message-ID: Date: Fri, 6 Nov 2026 21:58:49 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/memory_hotplug: don't offline a hwpoisoned page still in the page cache To: mt4022@columbia.edu, Oscar Salvador , Andrew Morton Cc: Miaohe Lin , Naoya Horiguchi , Vlastimil Babka , Gregory Price , linux-mm@kvack.org, linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org, tz2294@columbia.edu, stable@vger.kernel.org References: <20261105-memhp-hwpoison-pagecache-v2-1-029d35634d42@columbia.edu> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/5/26 21:50, Mani Tofigh via B4 Relay wrote: > From: Mani Tofigh > > Memory offline skips hwpoisoned pages, assuming nobody uses them > anymore. memory_failure() however sets PG_hwpoison before it takes the > page, and taking it waits on pcp_batch_high_lock, which offline_pages() > holds for the whole offline. A memory error during the offline thus > marks the page and then waits while the offline skips it: > > Task A (offline_pages) Task B (memory_failure) > zone_pcp_disable() > TestSetPageHWPoison(P) > get_hwpoison_page() > /* waits for Task A */ > do_migrate_range() > /* P is poisoned (not migrated) */ > test_pages_isolated() > /* P is poisoned (accepted) */ > zone_pcp_enable() > /* P is off the LRU (Ignored) */ > > The block goes offline while the file still points to P, and the next > walk of the file's pages (here drop_caches on ext4) crashes on a struct > page of offlined memory: > > [ 11.710348] Memory failure: 0x24224: unhandlable page. > [ 11.710372] Memory failure: 0x24224: recovery action for get hwpoison page: Ignored > [ 11.765371] page:000000008c304eee is uninitialized and poisoned > [ 11.765389] page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 0) > [ 11.765440] kernel BUG at include/linux/mm.h:1990! > [ 11.765458] Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI > [ 11.772284] CPU: 3 UID: 0 PID: 85 Comm: mfoffline Tainted: G W 7.3.0-17087-gd865f2677c44 #1 PREEMPT > [ 11.777970] RIP: 0010:find_lock_entries+0x8ee/0xad0 > [ 11.798761] Call Trace: > [ 11.799297] > [ 11.803284] mapping_try_invalidate+0xfd/0x2c0 > [ 11.810571] drop_pagecache_sb+0x111/0x330 > [ 11.811572] __iterate_supers+0x2e2/0x370 > [ 11.815863] drop_caches_sysctl_handler+0x74/0xb0 > [ 11.816994] proc_sys_call_handler+0x2ec/0x440 > [ 11.821360] vfs_write+0x545/0x1250 > [ 11.825220] ksys_write+0xfa/0x200 > [ 11.830202] do_syscall_64+0xfb/0x590 > [ 11.832084] entry_SYSCALL_64_after_hwframe+0x77/0x7f > [ 11.848423] > > Once the memory is also removed it's a use-after-free of the memory map. > tmpfs and the swap cache can end up the same way without the race. > Since commit a76054266661 ("mm: shmem: don't truncate page if memory > failure happens"), memory_failure() leaves a poisoned tmpfs folio in the > page cache on purpose, and it does the same for a dirty folio in the > swap cache. > > Treat a hwpoisoned page whose folio is still in a page cache or swap > cache as busy in scan_movable_pages() and > __test_page_isolated_in_pageblock() so that the offline fails and a > waiting memory_failure() can go on. Also have do_migrate_range() leave > such a folio alone instead of taking it off the LRU, so that > memory_failure() can still remove it from the cache. A later offline > succeeds once the page is out of the cache. With the fix, the offline > fails with -EBUSY and the file doesn't point to offlined memory anymore. > > This bug was identified and confirmed with the help of a deterministic > hypervisor currently under development. The C reproducer below however > hits it within about 10s. > > Fixes: b023f46813cd ("memory-hotplug: skip HWPoisoned page when offlining pages") > Cc: stable@vger.kernel.org > Signed-off-by: Mani Tofigh > --- > Changes in v2: > - Leave a hwpoisoned folio that is still in a page cache or swap cache > alone in do_migrate_range(), so that a waiting memory_failure() can > still remove it from the cache (Sashiko) > - Rebase onto current mm-new > - Link to v1: https://lore.kernel.org/all/20261101-memhp-hwpoison-pagecache-v1-1-ed8785ca44eb@columbia.edu/ > > A pinned hwpoisoned page still isn't covered. I'll send the refcount > check David suggested as a follow-up. I didn't understand why just checking for the refcount is not sufficient. Can you elaborate once more (and please not send a new revision before the discussion is over). Memory poisoning must grab a reference when setting the folio hwpoison. Any other reference (pin, pagecache, swapcache, mapping) keeps it alive. Why can't we build on and? -- Cheers, David