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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="Y8XX+R/3"; 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 9C6F3606A32E; Tue, 3 Nov 2026 15:12:27 +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=Y8XX+R/3 Received: by smtp.kernel.org (Postfix) with ESMTPSA id C7E921F000C1; Tue, 3 Nov 2026 15:12:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793718747; bh=zV1T+I0M/X5fYajz5gf/61terI3BQ0fU42btgMq0usc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Y8XX+R/34RU2qrAch5IzWEomeYhJRgnOPmQV0c1P4ua7aD9u6KoBL27GfTNHLhW4b M+894MvjRu0FPV7UZqNf0BqBv+B3NPVLyYnLJEUvBvfNhTYzb/ZTgeFtmB8zxvqN1L f8DVezDosMAJUoosTpIUr7qnBX3vQNbpsLPOOfx1bEe1EEFPm8kBu30mbWU4I3dxko 27z/yk6OveFo3E9sLlQLkZlcZpAGw3pxxon+OT0zrLkv7HhFxty/juVata4jEjgw0G 4p6/HQn1Ufn0qLwAYZn70b/sNfSCjlnNRLDhQhgy1o9iXAPrvL/jsm3XC4EJgColuC 3OGNqx1zKipNA== Message-ID: <6091a4d5-ded8-423e-a806-2c4b11f21e09@kernel.org> Date: Tue, 3 Nov 2026 16:12:20 +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 4/6] mm/page_alloc: don't undo another isolation in alloc_contig_range Content-Language: en-US To: "Gregory Price (Meta)" , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, surenb@google.com, mhocko@suse.com, brendan.jackman@linux.dev, hannes@cmpxchg.org, ziy@nvidia.com, linmiaohe@huawei.com, nao.horiguchi@gmail.com, david@kernel.org, ljs@kernel.org, liam@infradead.org, rppt@kernel.org, osalvador@suse.de, muchun.song@linux.dev, iamjoonsoo.kim@lge.com, anshuman.khandual@arm.com, stable@vger.kernel.org References: <20261027042204.3741307-1-gourry@gourry.net> <20261027042204.3741307-5-gourry@gourry.net> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/27/26 05:22, Gregory Price (Meta) wrote: > An alloc_contig_range() that overlaps a block going offline can leave > the offline spinning until it gets a signal, holding the device hotplug > lock. When isolation fails, alloc_contig_frozen_range() undoes it over > the whole range, clearing the offline's MIGRATE_ISOLATE too: > > CPU 1 (offline_pages) CPU 2 (alloc_contig_range) > start_isolate_page_range() > blocks are MIGRATE_ISOLATE > start_isolate_page_range() > -EBUSY on CPU 1's blocks > undo_isolate_page_range() > blocks are MIGRATE_MOVABLE > test_pages_isolated() > never succeeds again > > start_isolate_page_range() fails only on a block someone else isolated, > after undoing its own, so this undo only ever clears another caller's. > Return directly, as before alloc_contig_range() went pageblock granular. > > With offline_pages() parked after isolating a DIMM block and a 1G > hugetlb allocation made over it, the offline on base still loops 30s > later in 4 of 4 runs: > > offline_pages+0x5b2/0x1570 > memory_subsys_offline+0x17e/0x470 > device_offline+0x250/0x340 > state_store+0x88/0x110 > > With this patch the allocation still fails, and the offline completes in > 3 of 3 runs. > > Fixes: b2c9e2fbba32 ("mm: make alloc_contig_range work at pageblock granularity") > Cc: stable@vger.kernel.org > Signed-off-by: Gregory Price (Meta) I've applied this single patch to page_alloc/for-next-fixes and will drop the version from Josef [1]. Also transferred Zi's R-b since it's the same code change (plus comment). [1] https://lore.kernel.org/all/20261027-pgalloc-ai-hotfixes-v1-1-9c7d1aca801e@kernel.org/ > --- > mm/page_alloc.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 55d3fc4b307f5..bb3c7e95f2ed4 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -7396,9 +7396,13 @@ int alloc_contig_frozen_range_noprof(unsigned long start, unsigned long end, > * put back to page allocator so that buddy can use them. > */ > > + /* > + * On failure this has undone its own isolation, and any other > + * isolated blocks in the range belong to someone else, e.g. offline. > + */ > ret = start_isolate_page_range(start, end, mode); > if (ret) > - goto done; > + return ret; > > drain_all_pages(cc.zone); >