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 59F4138AC94; Thu, 12 Mar 2026 08:55:34 +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=1773305734; cv=none; b=nj2XFwBvR6s9OB+oSFKVxY8l8OaaXaAoNWP32rk/hsmldCDRJOqQbZisQQV7eRw9uabFkrRq7+87hbV3jQRXZ7kNqpFEfs+CVZn1LZLoNWjEWBFgxhfcLaSY5puTEFSZ2wKFZMChe1PaDOGZI6Td8eaRoMG2Q3o3DageOEo0ln0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773305734; c=relaxed/simple; bh=HxJoocjOCYFRNNtremEq4a9gZs6/4+/JZzLejhliau8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=MdMkvHS9596DXu+tlAv3u+UqEcHTOU8TKDXeEKFvQNlkezZjK+azaBSsw2pU9xm/OhL6n9VB+/SnYDoj+3UlHQTtSuYDw50IkVNcKVWPgilVjuZVUC6xQF5Bcd4jw0w/MR+Ux6p7OViLuGdLsorttByKCVbA3z+eZEWUoGyOBgU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mEzPIQnv; 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="mEzPIQnv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BE3B5C4CEF7; Thu, 12 Mar 2026 08:55:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773305734; bh=HxJoocjOCYFRNNtremEq4a9gZs6/4+/JZzLejhliau8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=mEzPIQnv7lpcbrKWbQSKEdwI+BmCAqv9+EhC7qg6Um/kMDsgtjDEe93CG4shWLgkg gqTkxBO8owX1eCgVCyx4jJCC43iB7ou0V0GuWAGcW4rXjypPMQUMV1pHreHaoZSDKe 4doGDFgYMIwDauXbDCHFPPI6z2ZD4esYqqhXADOo1YNu725Iay0VVjaoKiCt1hKmJc 5z1re9/loSTGJ3veQ+m5147YICU/ztkucG7JjDj1XR6jieHJI39l6UJDOsCaKjCuI1 GdaQ43Yxx/XLOEARcmwCeIU/9xKt1ar5josIKAZi6/s6pDw42HW20TQ4j3OQbO9tXM vv3OIO8m9oBhQ== Message-ID: Date: Thu, 12 Mar 2026 09:55:28 +0100 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] mm: prevent droppable mappings from being locked To: anthony.yznaga@oracle.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: akpm@linux-foundation.org, ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, jannh@google.com, pfalcato@suse.de, Jason@zx2c4.com, shuah@kernel.org References: <20260310155821.17869-1-anthony.yznaga@oracle.com> <9d90dd0b-1d60-4e45-922a-84637cab16a3@oracle.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 3/12/26 03:01, anthony.yznaga@oracle.com wrote: > > On 3/11/26 2:27 AM, David Hildenbrand (Arm) wrote: >> On 3/10/26 16:58, Anthony Yznaga wrote: >>> Droppable mappings must not be lockable. There is a check for VMAs with >>> VM_DROPPABLE set in mlock_fixup() along with checks for other types of >>> unlockable VMAs which ensures this when calling mlock()/mlock2(). >>> >>> For mlockall(MCL_FUTURE), the check for unlockable VMAs is different. >>> In apply_mlockall_flags(), if the flags parameter has MCL_FUTURE set, >>> the >>> current task's mm's default VMA flag field mm->def_flags has VM_LOCKED >>> applied to it. VM_LOCKONFAULT is also applied if MCL_ONFAULT is also >>> set. >>> When these flags are set as default in this manner they are cleared in >>> __mmap_complete() for new mappings that do not support mlock. A check >>> for >>> VM_DROPPABLE in __mmap_complete() is missing resulting in droppable >>> mappings created with VM_LOCKED set. To fix this and reduce that >>> chance of >>> similar bugs in the future, introduce and use vma_supports_mlock(). >>> >>> Fixes: 9651fcedf7b9 ("mm: add MAP_DROPPABLE for designating always >>> lazily freeable mappings") >> Should we Cc: stable? I think we should, to fix mlockall(MCL_FUTURE) >> behavior. > > I found this issue through code inspection while doing mshare dev work. > I don't have a strong idea how likely it is to happen in practice. If it > did it might not be easily diagnosed so I'm fine adding the tag. IIUC, mlockall(MCL_FUTURE) will result in future MAP_DROPPABLE mappings to get mlocked. I assume that implies that all pages will get faulted in and might not be reclaimable. With a quick test program that mmaps 4M, we indeed fault in all these pages (I assume you test does something similar). 7f5fc4600000-7f5fc4a00000 rw-p 00000000 00:00 0 Size: 4096 kB KernelPageSize: 4 kB MMUPageSize: 4 kB Rss: 4096 kB Pss: 4096 kB Pss_Dirty: 4096 kB Shared_Clean: 0 kB Shared_Dirty: 0 kB Private_Clean: 0 kB Private_Dirty: 4096 kB Referenced: 4096 kB Anonymous: 4096 kB KSM: 0 kB LazyFree: 0 kB AnonHugePages: 4096 kB ShmemPmdMapped: 0 kB FilePmdMapped: 0 kB Shared_Hugetlb: 0 kB Private_Hugetlb: 0 kB Swap: 0 kB SwapPss: 0 kB Locked: 4096 kB It's a good question whether memory reclaim would still be able to free these pages. I'd assume the folios would get mlocked and essentially turned unevictable -- breaking the whole concept of droppable mappings. So I think we should CC stable. -- Cheers, David