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 9C166BA34 for ; Fri, 19 Jun 2026 08:01:04 +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=1781856065; cv=none; b=qMJEm74J9MOhQDY41Xh+fvsUzWw3u9xKs/Ew572ahDb1vmRgC3gJixgLt5TIN/huX8j5qRJePfpWS2QJ5+Sr/v2U1ySa15tX8DCShR5NIM9ljVheWKOX5fesxvOuwx1K4eC2U3dQh/jBxGKSYoWhDUwsu6HZnNqgeWMPZN5+KVU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781856065; c=relaxed/simple; bh=klKztCGniK2qYHxcui066mzW0QAoA8wU6nmw1jZHw1Y=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=on23hh7R5aRlWo3ApaNcKHGd+4R0cKzQXpsSYkEP7b1EGU1T7M3Sx1c3d/xFGc3NsfjtAKoLiNwNIZyD5gO1YUPSUBZzdaeP8lsH7Bpbj3axFwZq89ckxLcVeLwSIboiE9da5WJII86XgSOj/elIARb0CFTepgl9t6CkdFnyX2s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UhGel73b; 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="UhGel73b" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 93E101F000E9; Fri, 19 Jun 2026 08:01:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781856064; bh=3ftbjs1r49TGSpHSfjI/+zcb2PtQ5xV2RKg9B5mDhpo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=UhGel73birqVS59+C/A/qJF4ZvqB42EErURgteqbJNSQRXzEVENe709aQPdpLkuJW z07gPHtgAOJzq6xD3TMihyzzzcbEGjz7diSII+m+3a+yP9fs+0mUNK9gUokGaaCLPG sKBZqfv8NtQVI6vudwTGAvX6nB/pAhLAFe1hhhwXLKHT57Lgu4F5otfyODoNdaaL+1 L5xGcCnR0Reo7J0SD0fok0oQZBNellpmARMZSRkxKlYzGAeVQ8qePzTKOlw01MF+zX 3KNqHgni83JwQXPw5ATx5MwSrC+gCWrlFSyYDUbWjaIfjqEkXypKHGu+66a+AUz5v2 s+O2Gk31XHQ2g== Message-ID: <3149fcee-eded-49b0-baf4-ab69c27ff063@kernel.org> Date: Fri, 19 Jun 2026 10:00:59 +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: [PATCH] mm: page_ext: validate section in for_each_page_ext iterator To: Luiz Capitulino , Ketan , Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan Cc: kernel@oss.qualcomm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260617-page_ext-v1-1-37ad802b1a38@oss.qualcomm.com> <1dbebf73-6c46-44e1-ac6a-f5ffa9849b37@kernel.org> <698e5cdc-8f1d-4984-bb54-a4b7979b4dc8@redhat.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 6/19/26 04:38, Luiz Capitulino wrote: > On 2026-06-18 05:04, David Hildenbrand (Arm) wrote: >> On 6/17/26 17:09, Ketan wrote: >>> The page_ext iteration API do not validate if the PFN still >>> belongs to a valid section while advancing the iterator. >>> >>> When dynamically adding memory in hotplug path, it can lead >>> to a NULL pointer dereference during page_ext_lookup at the >>> boundary of the last valid section. >>> >>> [   14.555124][  T846] Call trace: >>> [   14.555125][  T846]  lookup_page_ext+0x6c/0x108 (P) >>> [   14.555127][  T846]  page_ext_lookup+0x30/0x3c >>> [   14.555129][  T846]   +0x11c/0x260 >>> [   14.571201][  T846]  __free_pages_ok+0x5e8/0x8e0 >>> [   14.571204][  T846]  __free_pages_core+0x78/0xf0 >>> [   14.571206][  T846]  generic_online_page+0x14/0x24 >>> [   14.597782][  T846]  online_pages+0x178/0x30c >>> [   14.597784][  T846]  memory_block_change_state+0x284/0x32c >>> [   14.597787][  T846]  memory_subsys_online+0x4c/0x64 >>> [   14.597789][  T846]  device_online+0x88/0xb0 >>> [   14.597791][  T846]  online_memory_block+0x30/0x40 >>> [   14.597793][  T846]  walk_memory_blocks+0xac/0xe8 >>> [   14.597794][  T846]  add_memory_resource+0x280/0x298 >>> [   14.656161][  T846]  add_memory+0x60/0x98 >> >> So, we do allocate the page_ext in memory_notify(MEM_GOING_ONLINE) -> ... >> page_ext_callback() -> online_page_ext(). >> >> Which makes sure that all page_ext is actually allocated (for the full section). >> >> So when we later end up in generic_online_page(), the page_ext should be there >> and the memory section should be valid. >> >> >> How can online_pages(), which onlines memory part of present memory sections, >> online (free) memory that suddenly does not belong to a present memory section? >> >> Something doesn't make sense here. > > Ketan, would you please share the full OOPs message and maybe tell us > how you reproduce this issue? Ah, I think I figured it out. for_each_page_ext() does a "__page_ext = page_ext_iter_next(&__iter)" and the end. That is the real problem and should be spelled out in the patch description. Likely we should just handle that in the iterator, looking up page-ext for something that doesn't exist is weird. >From ce41607a4e4c1d872b6d3050da2e24d41a30d822 Mon Sep 17 00:00:00 2001 From: "David Hildenbrand (Arm)" Date: Fri, 19 Jun 2026 09:58:46 +0200 Subject: [PATCH] tmp Signed-off-by: David Hildenbrand (Arm) --- include/linux/page_ext.h | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h index 61e876e255e8..468c074582e1 100644 --- a/include/linux/page_ext.h +++ b/include/linux/page_ext.h @@ -112,6 +112,7 @@ static inline struct page_ext *page_ext_next(struct page_ext *curr) struct page_ext_iter { unsigned long index; + unsigned long pgcount; unsigned long start_pfn; struct page_ext *page_ext; }; @@ -120,15 +121,19 @@ struct page_ext_iter { * page_ext_iter_begin() - Prepare for iterating through page extensions. * @iter: page extension iterator. * @pfn: PFN of the page we're interested in. + * @pgcount: number of page_ext entries to iterate * * Must be called with RCU read lock taken. * * Return: NULL if no page_ext exists for this page. */ static inline struct page_ext *page_ext_iter_begin(struct page_ext_iter *iter, - unsigned long pfn) + unsigned long pfn, unsigned long pgcount) { + VM_WARN_ON_ONCE(!pgcount); + iter->index = 0; + iter->pgcount = pgcount; iter->start_pfn = pfn; iter->page_ext = page_ext_lookup(pfn); @@ -149,8 +154,9 @@ static inline struct page_ext *page_ext_iter_next(struct page_ext_iter *iter) if (WARN_ON_ONCE(!iter->page_ext)) return NULL; + if (++iter->index >= iter->pgcount) + return NULL; - iter->index++; pfn = iter->start_pfn + iter->index; if (page_ext_iter_next_fast_possible(pfn)) @@ -183,9 +189,9 @@ static inline struct page_ext *page_ext_iter_get(const struct page_ext_iter *ite * IMPORTANT: must be called with RCU read lock taken. */ #define for_each_page_ext(__page, __pgcount, __page_ext, __iter) \ - for (__page_ext = page_ext_iter_begin(&__iter, page_to_pfn(__page));\ - __page_ext && __iter.index < __pgcount; \ - __page_ext = page_ext_iter_next(&__iter)) + for (__page_ext = page_ext_iter_begin(&__iter, page_to_pfn(__page), __pgcount);\ + __page_ext; \ + __page_ext = page_ext_iter_next(&__iter)) #else /* !CONFIG_PAGE_EXTENSION */ struct page_ext; -- 2.43.0 -- Cheers, David