From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B926E31F99A for ; Wed, 11 Mar 2026 13:57:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773237440; cv=none; b=VMbE2oZkDKrs+4iIkUi/PfUKfh0DfA+HgnsVR3ZFkpx/UShRsD44sY3Cm7g77grUbBqsRVHw1ZYNLdUss2BWVkh0YCzN6YJ2zYIWC4hWfMcTcf/q5cJpFE3ujnmXsNYAnTLDwKdmCI33bEWM0PHUzTEzp5fjul84EWBLasnCGcA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773237440; c=relaxed/simple; bh=FufJY4hvTCH40qFLkuAK2NFVy71xbnZqN98KKnD052s=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Rvk9nQ3cKNlmH7hNujb99fCH/GgFqjKAFn/0K2Fa0dCO3dgP+d2VqM/2WFAz6H4kBMO92GCVrHpqC3j1vW9SHaETAy9zHfuUJv5bppyuGKs8sDnPSsgCfz54lk/tiRHG36h5QOTbWs+OvMtUeT6L2rZ03J4Cq37ejpUvMICaNlI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ThdfCY7u; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ThdfCY7u" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 453AFC4CEF7; Wed, 11 Mar 2026 13:57:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773237440; bh=FufJY4hvTCH40qFLkuAK2NFVy71xbnZqN98KKnD052s=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ThdfCY7uv+bCmSMV0tDzf6VHVA6Jdq9XCJ+RRUYsmyC8OV3SYwg2agPWYsoJkT1hs NXctXTMpjZMDBVaWzYrLsQc6ibzOn3JMEYneFHA4YJQXdbpwuAj8iW7a9mRHJCZENv ycv8hQgqpCPRxCUIVE1fi+2sQs0DVfe8+4gGTt1JfujcfyT41J/2E9fkU/74c9cRk2 iYjH1+abmn4GcSECttN30LIj2KDjX030XG6Gh6z2GWivGTXlCcRH6+3oaCkAjF258i +cWKoMyEugZ2xSLLklhvgVw5kze4EAvzLhM4NZSxN2F5zgg5B42A3x0Qj7ThFMNhOY MnAtuI1Wr829g== Message-ID: <6678200f-92dc-4ab4-8bc0-d956bcea528a@kernel.org> Date: Wed, 11 Mar 2026 14:57:15 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: migrate: transfer large_rmappable flag in folio_migrate_flags() To: Zi Yan Cc: Usama Arif , Andrew Morton , npache@redhat.com, willy@infradead.org, linux-mm@kvack.org, matthew.brost@intel.com, joshua.hahnjy@gmail.com, hannes@cmpxchg.org, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20260311132342.3193160-1-usama.arif@linux.dev> <46edc7f1-f97e-4ff3-bf11-a56feb8e33b4@kernel.org> <1DA53E52-795E-4057-81F5-E39B85D7CF05@nvidia.com> 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 3/11/26 14:38, Zi Yan wrote: > On 11 Mar 2026, at 9:33, David Hildenbrand (Arm) wrote: > >> On 3/11/26 14:23, Usama Arif wrote: >>> folio_migrate_flags() transfers folio state from source to destination >>> during migration, but does not transfer the large_rmappable flag. >>> >>> Migration allocators like alloc_migration_target() and >>> alloc_misplaced_dst_folio() use __folio_alloc() directly without >>> wrapping the result in page_rmappable_folio(), so the destination folio >>> never gets large_rmappable set. >>> >>> This becomes a problem when a folio on the deferred split queue is >>> migrated: the destination folio can be added to the deferred split queue >>> via deferred_split_folio() (which does not check large_rmappable), but >>> when the folio is later freed, folio_unqueue_deferred_split() bails out >>> early because large_rmappable is not set: >>> >>> if (folio_order(folio) <= 1 || !folio_test_large_rmappable(folio)) >>> return false; >>> >>> This leaves a stale entry on the deferred split queue, leading to >>> use-after-free when the shrinker walks the list. >>> >>> Fix this by transferring large_rmappable in folio_migrate_flags(), >>> consistent with how all other folio flags are handled. >>> >>> Fixes: dafff3f4c850 ("mm: split underused THPs") >>> Signed-off-by: Usama Arif >>> --- >>> mm/migrate.c | 3 +++ >>> 1 file changed, 3 insertions(+) >>> >>> diff --git a/mm/migrate.c b/mm/migrate.c >>> index 3380021fd3db..ee1c7bc851dd 100644 >>> --- a/mm/migrate.c >>> +++ b/mm/migrate.c >>> @@ -846,6 +846,9 @@ void folio_migrate_flags(struct folio *newfolio, struct folio *folio) >>> folio_copy_owner(newfolio, folio); >>> pgalloc_tag_swap(newfolio, folio); >>> >>> + if (folio_test_large_rmappable(folio)) >>> + folio_set_large_rmappable(newfolio); >>> + >>> mem_cgroup_migrate(folio, newfolio); >>> } >>> EXPORT_SYMBOL(folio_migrate_flags); >> >> compaction_alloc_noprof() does the page_rmappable_folio() at the end. >> >> I'd assume that all migration allocation functions must take care of that. >> >> It's a responsibility of the folio allocation code, not folio migration >> code. > > I agree. The migration allocation function needs to give a folio or other > types of page matching the original one. Do we want to turn this into > a WARN to make sure newfolio matches folio's large_rmappable state? VM_WARN, sounds reasonable. -- Cheers, David