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 9881339902B; Mon, 27 Apr 2026 08:00:21 +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=1777276821; cv=none; b=cj6N6ZrvuaI9tSYEwMgeqxbOp4UlzUq/VKh65mJIH4Pysf6KAfIQiCj7qpC82ooFVq0QO/qGKbRGYRkWHIIlD3hAZSLwhMd5Y/vnI5z+q3yeyiHhKmKPDTDHjCgHZWTreLmZpzzkODP+ab/myPxOLEFpZ+s8Es1p3UGNoZ9+VUs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777276821; c=relaxed/simple; bh=6lSQYBY2+IuLHDfyeYcIQP7M9ufPZ8ri79+137pQ1+w=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZpVpc06IyC4B0XuxhBQ4d93i/wgF6c5PZJn47Gvmme6N+Rb5WQv7VasDNnXswcxApoOpsPw4HWR/YX2Raaul/VVRgvNbIz3pXdavq9l491mDPACc/fon95s8p2jE8vaJusiG3gwp2pQK+rNfRyRAILWw9/yu9SAs+dUhVb+KewU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=vNZsVs5d; 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="vNZsVs5d" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4FDABC19425; Mon, 27 Apr 2026 08:00:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777276821; bh=6lSQYBY2+IuLHDfyeYcIQP7M9ufPZ8ri79+137pQ1+w=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=vNZsVs5dlJ6IIUwPClc7UZHRymQhjIiYtz4kz7lvFmHQK3+4MOCMw8gtFBpQFAy+c HLiRM0b1nxo6h1KtTqewlfvqG92VW6laNBiW4JdS7lf0apSF9XsJ+6jgf4HGTHsnLB FV2HKV1iVmhhpvKUPno4SpNZXdAektVWSB3+CntNHeor54MMpLDARIaAHT/ZtYf+6P /fv4A+8woGTR4scKjC6Gqh+idMLufSrwNEy8xxZRTkBQA2GzO9RVyUt6ZTsYFIv/fe 2rEtyeSGu74o8HZDeVjqdvh3Dyd8AGTmbxAj2QnFT4hlQkZuF7/w4AbYrSR0mryuTH w1r1neGMuyw7A== Message-ID: Date: Mon, 27 Apr 2026 10:00:16 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-hotfixes v2 0/2] mm/page_alloc,slab: return NULL early from *_nolock() memory allocation APIs in NMI on UP Content-Language: en-US To: "Harry Yoo (Oracle)" , Andrew Morton , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Shakeel Butt , Alexei Starovoitov , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260427-nolock-api-fix-v2-0-a6b83a92d9a4@kernel.org> From: "Vlastimil Babka (SUSE)" In-Reply-To: <20260427-nolock-api-fix-v2-0-a6b83a92d9a4@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/27/26 09:09, Harry Yoo (Oracle) wrote: > Due to my mistake, V1 was sent twice w/o proper cover letter and > Cc: stable. Please ignore V1. Apologies for the noise. > > Changes since V1: > - used b4 to send patch series (w/ a proper cover letter) instead of > my broken git send-email script (Thanks Vlastimil) > - added Cc: stable to patches 1 and 2 > > On UP kernels (!CONFIG_SMP), spin_trylock() is a no-op that > unconditionally succeeds even when the lock is already held. > As a result, alloc_frozen_pages_nolock() and kmalloc_nolock() called > from an NMI context can successfully re-acquire the lock that the > page/slab allocators are already holding (no deadlock because it's > trylock, but leads to e.g., allocating the same page/object twice and > causing use-after-free). > > It was discovered while testing the new kmalloc/kfree_nolock() test case > in the slub_kunit test module with CONFIG_DEBUG_SPINLOCK=y on a UP > kernel. > > Patch 1 fixes alloc_frozen_pages_nolock() and > patch 2 fixes kmalloc_nolock(). Thanks. Given the problem exposed is in a slab kunit test I think it's better to handle this in the slab tree. The page_alloc change is small and should not cause conflicts. So I've merged both in slab/for-next. > Note: As pointed out by Vlastimil Babka [1], in theory a kprobe in a > locked section could trigger the same issue. However, fixing that > involves a non-trivial rework (e.g., inventing a new spinlock type) or > introduces unnecessary overhead for all spinlocks on UP (e.g., let all > spinlocks check locked status on UP). > > Given that BPF tracing on UP is rare, and it's even more unlikely to > trace a function called from the memory allocator within the locked > section, this patch series addresses the issue only on NMI contexts > (which is rare as well but now covered by the new test case). > > [1] https://lore.kernel.org/linux-mm/af3a7fa9-b368-4ffd-964d-9e4fcba863a8@kernel.org > > Cc: stable.vger.kernel.org > --- > Harry Yoo (Oracle) (2): > mm/page_alloc: return NULL early from alloc_frozen_pages_nolock() in NMI on UP > mm/slab: return NULL early from kmalloc_nolock() in NMI on UP > > mm/page_alloc.c | 5 +++++ > mm/slub.c | 4 ++++ > 2 files changed, 9 insertions(+) > --- > base-commit: ba24da38a519dfcff8cce3f3f2726d7b159a4d75 > change-id: 20260427-nolock-api-fix-bd056911e68e > > Best regards, > -- > Cheers, > Harry / Hyeonggon >