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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=iSuGB1Vz; 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 B6DAF606A324; Mon, 2 Nov 2026 06:56:32 +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=iSuGB1Vz Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0C08C1F000C1; Mon, 2 Nov 2026 06:56:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793602592; bh=bCDf4ZW3rE+CGNZfOsXMT1wgJaQq6SHV/zB4PxcXzws=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=iSuGB1Vz47JLVuaefZLVIZbkKz4UmxB7ofSbm1uICkj4KSw6wznxNSxosbBdF/Myj 1172MZCKJE+mCnBhjE0+n392O0Xy17f1ZRp1kugIyZiNlEFqdCZlnm41tX9BtY8YMw g4kKoG9kky/Cjzl9ygn5On1pV7zLTQFlUOq22z8XU++r5vbcPVlEt2Oxi9SmnBIJWF dKMjleveJCPhmc5m5J/2X63qnk+rY9WZk9P4wRRG+hPV9jXlncLZL74wcu/wbmPGNg sg4Yfxwd4ivD2/RW9Qh7dpXCxMg8aLA0gM3MipHCDq+udFLRKarizzHSIf+43c6z3L vthFWNjBRaSHA== Message-ID: <1b6a6d13-8a01-414b-9bbe-cd194af1f539@kernel.org> Date: Mon, 2 Nov 2026 07:56:27 +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] 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: <20261101-memhp-hwpoison-pagecache-v1-1-ed8785ca44eb@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 11/1/26 20:40, 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. 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 > --- > Taking get_online_mems() in memory_failure(), as in Gregory's series > [1], would close only the race and not the tmpfs or swap cache case. > > [1] https://lore.kernel.org/all/20261027042204.3741307-4-gourry@gourry.net/ > > Reproducer: https://github.com/manitofigh/files/blob/main/linux-repros/mfoffline.c > --- > mm/internal.h | 9 +++++++++ > mm/memory_hotplug.c | 2 ++ > mm/page_isolation.c | 2 +- > 3 files changed, 12 insertions(+), 1 deletion(-) > > diff --git a/mm/internal.h b/mm/internal.h > index aeebb3e49ed1..ba7b1650a5ca 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -1195,6 +1195,15 @@ static inline int unmap_poisoned_folio(struct folio *folio, unsigned long pfn, b > } > #endif > > +/* > + * A hwpoisoned page can be skipped by memory offline only once no page > + * cache or swap cache can find it anymore. > + */ > +static inline bool hwpoison_page_offlineable(const struct page *page) > +{ > + return !folio_mapping(page_folio(page)); > +} > + > extern unsigned long __must_check vm_mmap_pgoff(struct file *, unsigned long, > unsigned long, unsigned long, > unsigned long, unsigned long); > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index c9cc42e54f05..3d36f7f2e04b 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1820,6 +1820,8 @@ static int scan_movable_pages(unsigned long start, unsigned long end, > struct folio *folio; > > page = pfn_to_page(pfn); > + if (PageHWPoison(page) && !hwpoison_page_offlineable(page)) > + return -EBUSY; > if (PageLRU(page) || page_has_movable_ops(page)) > goto found; > > diff --git a/mm/page_isolation.c b/mm/page_isolation.c > index 5aaad037384e..beb09ef345ee 100644 > --- a/mm/page_isolation.c > +++ b/mm/page_isolation.c > @@ -593,7 +593,7 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn, > */ > pfn += 1 << buddy_order(page); > else if ((mode == PB_ISOLATE_MODE_MEM_OFFLINE) && > - PageHWPoison(page)) > + PageHWPoison(page) && hwpoison_page_offlineable(page)) I was recently wondering about that one as well. What if we still have the page pinned somehow? (vmscplice etc). Wouldn't it be better to make sure that poisoning code holds exactly one reference (whoever set hwpoison) and check here that the refcount is 1 ? Pagecache references would turn it > 1. A note that I consider this here extremely low priority. -- Cheers, David