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 A0A2D2F068F; Mon, 17 Nov 2025 16:47:19 +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=1763398039; cv=none; b=aoGhyOf7jLKJMeYe7eBV6wWxaYHoprUnLhNtBqn/XD71OmV1V9uMp7lTofZ1ZqPa6kJEhNL0YSr6grWvuuOCGtgpKy7eL3Ghw+ERsQ16ewJJ8AWSobHmsCjcLIXRpssVYIYWC9ayRJpzfn+Zr24931CrBwtrtpc1FqbPNGONJQc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763398039; c=relaxed/simple; bh=VDPU8WBpaSMdog+Adn5C5R/6IBPWeQhuaPBSI4eT7Ko=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=VAsAYPEaQjJEAOlb8qYfBp+dHLWMMeBcO3WBARYh5YacGJws6ma3E+kL1UZgUaoq/ezXZCqPOLBJXoXUmtlCugw8FJXXJBoMZhrMTB1OGQ3ZVd9J592Dz4L4YCU8bkWl8ETymCLZZlPjD1rPefLzNGgKfT62KUtXAO9R5kH18Ec= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=I4mLEid5; 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="I4mLEid5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 818FDC4AF0B; Mon, 17 Nov 2025 16:47:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763398039; bh=VDPU8WBpaSMdog+Adn5C5R/6IBPWeQhuaPBSI4eT7Ko=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=I4mLEid5UB2vfOwQXMYCyyiehnTm4dhzeg8ijCEtfD2upmwu1wXdOEhJ+MLKn5PyL XWjEQLi4Gkzt61V91UBFEXN4IvveVwebdp3HmwNGmDyTT3QB4mXI5bbIo+K+MmoMNn LgsO/tTrW0XgeARy9TG+bmFaCZbslP/UdD/1PnRitn2CLZfBffpDBprSsOJ/9yJEL0 5G7QezrhBDd/ytSQhI+YTKE0+c7cXgDd5CnuaNKFtHucUrNJE4J+3snXSh/O5y+7ju 5mJjRxcNDM8F9XTrK87uvomDx9F2hDcRKfm4olTCbOTtGNf6+tq4xFxicNH+bG1uM4 6zkTWIT+Y7vaQ== Message-ID: Date: Mon, 17 Nov 2025 17:47:05 +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: [RFC mm v6] mm: introduce a new page type for page pool in page type To: Jesper Dangaard Brouer , Byungchul Park , linux-mm@kvack.org, netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel_team@skhynix.com, harry.yoo@oracle.com, ast@kernel.org, daniel@iogearbox.net, davem@davemloft.net, kuba@kernel.org, john.fastabend@gmail.com, sdf@fomichev.me, saeedm@nvidia.com, leon@kernel.org, tariqt@nvidia.com, mbloch@nvidia.com, andrew+netdev@lunn.ch, edumazet@google.com, pabeni@redhat.com, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, horms@kernel.org, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, ilias.apalodimas@linaro.org, willy@infradead.org, brauner@kernel.org, kas@kernel.org, yuzhao@google.com, usamaarif642@gmail.com, baolin.wang@linux.alibaba.com, almasrymina@google.com, toke@redhat.com, asml.silence@gmail.com, bpf@vger.kernel.org, linux-rdma@vger.kernel.org, sfr@canb.auug.org.au, dw@davidwei.uk, ap420073@gmail.com, dtatulea@nvidia.com References: <20251117052041.52143-1-byungchul@sk.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 17.11.25 17:02, Jesper Dangaard Brouer wrote: > > On 17/11/2025 06.20, Byungchul Park wrote: >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 600d9e981c23..01dd14123065 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -1041,7 +1041,6 @@ static inline bool page_expected_state(struct page *page, >> #ifdef CONFIG_MEMCG >> page->memcg_data | >> #endif >> - page_pool_page_is_pp(page) | >> (page->flags.f & check_flags))) >> return false; >> >> @@ -1068,8 +1067,6 @@ static const char *page_bad_reason(struct page *page, unsigned long flags) >> if (unlikely(page->memcg_data)) >> bad_reason = "page still charged to cgroup"; >> #endif >> - if (unlikely(page_pool_page_is_pp(page))) >> - bad_reason = "page_pool leak"; >> return bad_reason; >> } > > This code have helped us catch leaks in the past. > When this happens the result is that the page is marked as a bad page. > >> >> @@ -1378,9 +1375,12 @@ __always_inline bool free_pages_prepare(struct page *page, >> mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1); >> folio->mapping = NULL; >> } >> - if (unlikely(page_has_type(page))) >> + if (unlikely(page_has_type(page))) { >> + /* networking expects to clear its page type before releasing */ >> + WARN_ON_ONCE(PageNetpp(page)); >> /* Reset the page_type (which overlays _mapcount) */ >> page->page_type = UINT_MAX; >> + } >> >> if (is_check_pages_enabled()) { >> if (free_page_is_bad(page)) > > What happens to the page? ... when it gets marked with: > page->page_type = UINT_MAX > > Will it get freed and allowed to be used by others? > - if so it can result in other hard-to-catch bugs Yes, just like most other use-after-free from any other subsystem in the kernel :) The expectation is that such BUGs are found early during testing (triggering a WARN) such that they can be fixed early. But we could also report a bad page here and just stop (return false). -- Cheers David