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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=BNoPTNH2; 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 E8ECA606A31B; Tue, 27 Oct 2026 13:37:10 +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=BNoPTNH2 Received: by smtp.kernel.org (Postfix) with ESMTPSA id EBAB21F01825; Tue, 27 Oct 2026 13:37:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793108230; bh=xeh0h8/al9334KMAYnmna8mlBpnyruhKQ6eKh9bOxag=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=BNoPTNH2mY6hAGlBSJMX1nCiPi/BoGcEcnnfFq6+h+wDjw1G0y3hs+ebQAtAiOELD yJgwrrd+Ds0GpFEn8jauqMs8Ehpf+VQDtoj4/b6jGVizI7Ad9DgH0pv2uuAGGif266 OEHVIx4AvTC1axwF8GssWq1nVxDxxYHCzUnB9V7JIgH/pNrP9bqVUhtnJW/Ac4lRbX fIDxYERC1b21qEqhiEx+KpoEDgSx9BuagIKuqrxTN4GJvtB90vSRNFLEQgrldSHxxm LsT5zfRiRhFmJ0HPZLYF4fdDqnqwgIEqAH7zIVU2uyHIUGvEyYpQ3IINiIuWcUgelT o6ASz9eiq/Z3w== Message-ID: Date: Tue, 27 Oct 2026 14:37:01 +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 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, vbabka@kernel.org, surenb@google.com, mhocko@suse.com, brendan.jackman@linux.dev, hannes@cmpxchg.org, ziy@nvidia.com, linmiaohe@huawei.com, nao.horiguchi@gmail.com, 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: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@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) > --- We have an existing AI fix for that as well already handled by Vlasta. I think we'll have to establish some model of "ask David first before posting" because otherwise we just create duplicate work for everyone. -- Cheers, David