From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 3692924B28 for ; Thu, 20 Aug 2026 18:16:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787249779; cv=none; b=X335QzE/bw9N+pdyAezFpeC49zN6mg/7TRNAJ/NbJQjvXE2jRQ48vAEH3fcXiV6pNliebf9ejpFGZVM3lQwQGPR/ZERv9SOm9Fvu30B6fs4qXX1f624WLH25s67uU0Fx2dSyS3Ol347Jow+2gVYoYlrTlg5ng65n8j7b4Y7wCFw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787249779; c=relaxed/simple; bh=IcxKmWXwaYYuGGHDsuHRuFqZSuya7HOdw31mcrE/Sbc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JnzJkDLauk5m4nLrCjHUqSjsRvqaI6FUQ9amRtLsXp5XEQamBDTJppprEOiqJV6RjSioBk5kydydUeHhdooiGy0FT0U693PX8MUT3gN0Js8eapuIdWIaguZ2sQsNPE8PfpqD5zOaoVrtWA0edUFaQ9E4eVaDTIH/sJvucir5qc4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OmApUQTy; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="OmApUQTy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 126BE1F000E9; Thu, 20 Aug 2026 18:16:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787249777; bh=1qzXwSGRzxXf3Jyr1Li0HuCFQ/7f8KQjrL120t1/X8o=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=OmApUQTy2/X8U2UCuK4noYx54xutL+aqvVshtWwIDIG637qlVRcWR31STHsM1nr8A AsOgkZ7iVvWRFnlBvhJsNtT4OL38pvn9saS+tXz0388CxnSm6CxDvxbzgA0zNKFBTG wj96dr0nonXho6K9Wm0t5rZCMuiLVPcz1EbOaKKgWtqZS2L0S40YbVJE9QURVMEW/Z +Mn0CuaYK7+FnA9bNS25q9PWegwOkW1Dtl+2LX6xN6A9JSQ7b8oHHj7OBBNEjDvp7W sebiPerZO/zOahgTo+0sUs5y2a+Y4ea4w0bTruySB3BbiJ7GGKvmiODELNlNaoXyWw 728MBcHmvIdqg== Message-ID: Date: Thu, 20 Aug 2026 20:16:13 +0200 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: [RFC PATCH v3] mm/cma: don't release CMA pages still in use To: Rik van Riel Cc: Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260811132045.5f114772@fangorn> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260811132045.5f114772@fangorn> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/11/26 19:20, Rik van Riel wrote: > When a driver calls dma_free_contiguous() before quiescing DMA, the > page still has a reference from the device. put_page_testzero() there > returns false, WARN fires, but the code proceeds to > free_contig_frozen_range() putting a live page onto buddy and clearing > the bitmap. A subsequent allocation can hand the same PFN to a new > owner while the original holder still references it. > > A concurrent put_page() that drops the last reference between the > testzero loop and free_contig_frozen_range() can double-queue the page > via page->lru, corrupting buddy lists. > > Avoid the corruption by not freeing a CMA region if any of the > pages inside are still in use. > > Make it explicit in the warning that the driver allowed a leak. > > Fixes: 9bda131c6093 ("mm: cma: add cma_alloc_frozen{_compound}()") > Link: https://lore.kernel.org/linux-mm/20260809210608.06b5ccb9@fangorn/ [v1] > Link: https://lore.kernel.org/linux-mm/20260810122737.030f8452@fangorn/ [v2] > Cc: stable@vger.kernel.org As discussed, I don't like stable here. Fixes is debatable (code was more robust before 9bda131c6093). Code that actually triggers this is the problematic code, this here is rather making the code more robust for buggy drivers. > Signed-off-by: Rik van Riel > --- > v3: > - simplify things by simply leaking the CMA range, drivers should not > call cma_release() while the space is still in use (David Hildenbrand) > > mm/cma.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/mm/cma.c b/mm/cma.c > index a13ce4999b39..c1425f25c39b 100644 > --- a/mm/cma.c > +++ b/mm/cma.c > @@ -1018,7 +1018,7 @@ bool cma_release(struct cma *cma, const struct page *pages, > unsigned long count) > { > struct cma_memrange *cmr; > - unsigned long ret = 0; > + unsigned long leaked = 0; > unsigned long i, pfn; > > cmr = find_cma_memrange(cma, pages, count); > @@ -1027,9 +1027,12 @@ bool cma_release(struct cma *cma, const struct page *pages, > > pfn = page_to_pfn(pages); > for (i = 0; i < count; i++, pfn++) > - ret += !put_page_testzero(pfn_to_page(pfn)); > + leaked += !put_page_testzero(pfn_to_page(pfn)); > > - WARN(ret, "%lu pages are still in use!\n", ret); > + if (leaked) { > + WARN(1, "%lu pages are still in use, not freeing CMA region!\n", leaked); > + return true; > + } > > __cma_release_frozen(cma, cmr, pages, count); > Okay, that will leave the frozen and the CMA bits remains set. It's a bit inconsistent, because pages the buggy driver will release later will end up in the buddy, whereby pages we just freed will not end up in the buddy. We could consider the following instead: leaked += !page_ref_freeze(pfn_to_page(pfn), 1); (I hope I got that conditional right) Then we will just consistently leak all pages (keeping them allocated with a refcount of 1). Oh, and it nicely matches the "__cma_release_frozen" terminology later ;) (on a related note, the code in general looks a bit shaky regarding speculative references, but we saw no reports so far ... it will all get clearer once more code is converted to use frozen pages so we won't even run into this) -- Cheers, David