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 23C3133D4E9; Wed, 30 Sep 2026 16:46:26 +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=1790786788; cv=none; b=BAIUgkxnK5jTGDrPGwJnpgEoVwmHLvWYFavZnb0lPJDE2fYJWLoAzhbnwLHHQdDZ2lJ2DJuNa28dSNWqMovDxYCHXaKBPHL0gtSwesBvw6/J3OAoYAgA9o3OcVE1D+hJ4QzH+rJkbmK24rZvmVgxMeW7sl2EErF3igZaxOSqEAk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790786788; c=relaxed/simple; bh=9Ye/2uPBM5l23jTZ7szq8OrrIihr83041xy3JF7nfx8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=itVc1a8VjNNGm5SpP06ax6omNR5vVAC1zaALvcU1YT9BJ5sIPaSnwVlH5uuKc8A6m8BmExzYls0LLMMFGiJYByze/4fTyduaZKAg+A4WQVcOdz4+hC0B1t81zTv9TBldRuOI3Z9c5WVBV1v5nbuJz5LVO31qF4pro9hn9sTPCZM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cbpZZvN1; 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="cbpZZvN1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3FC1D1F00893; Wed, 30 Sep 2026 16:46:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790786786; bh=xMQrpTVfG24oup9/xVlbB5NV7FVEZ7+5pDyeSSmpyfs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=cbpZZvN1V4yJhr0654j0pNRf6FbcuIx6mTMvt1ROw6G9X1SImEmMDOJ8lH1jBsd7o PCYd8QZSQxPI3rWir6g0spJlEVytWn5Aj0Z9YDz+Zs0RjPHXjxWwZPO+Gh+7AoQRT2 2Pazx6lAvyFTAezAxSfnddj4eTjun3C5nXk3/h/unfXMMJA1HapLsKbUObn0MyoMX+ ZyyEwpScnoo3K1x1ZcyOlP+WsdL9Bmall51adOCKtDYfcGY+wrBESCcFjoj3xY1Gok CCMlpYOTN8a6Iy3/fVzKtd3gBDKV426pk/v88DTkF1VbsHtNukMjCw3fGlvxjCtPbz vKUfzJ2aNbdOg== Message-ID: Date: Wed, 30 Sep 2026 18:46:21 +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 1/1] mm/memory_hotplug: fix missing rollback in __add_pages() To: Lance Yang , osalvador@suse.de Cc: akpm@linux-foundation.org, muchun.song@linux.dev, linux-mm@kvack.org, linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260930160432.5564-1-lance.yang@linux.dev> 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 9/30/26 18:04, Lance Yang wrote: > __add_pages() returns on a sparse_add_section() failure without removing > the sections already added in the same request. > > For memremap_pages(), the failed range is not counted in pgmap->nr_range, > so memunmap_pages() skips it. The sections already added in that range > retain their vmemmap mappings and subsection bits. Retrying a > section-aligned range can then fail with -EEXIST. > > Save the initial PFN and remove [start_pfn, pfn) on failure. For a vmemmap > population failure, section_activate() already cleans up the current > section, so the rollback excludes it. If the first section fails, > __remove_pages() receives an empty range and does nothing. > > Link: https://lore.kernel.org/all/BAD58999-1EDD-4A37-ABA0-DB1BD8AB3453@linux.dev/ > Suggested-by: Muchun Song > Signed-off-by: Lance Yang > --- > No Fixes tag, as I couldn't identify the commit that introduced this issue. > > mm/memory_hotplug.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 796af1028ee2..ca4656698148 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -380,6 +380,7 @@ EXPORT_SYMBOL_GPL(pfn_to_online_page); > int __add_pages(int nid, unsigned long pfn, unsigned long nr_pages, > struct mhp_params *params) > { > + const unsigned long start_pfn = pfn; > const unsigned long end_pfn = pfn + nr_pages; > unsigned long cur_nr_pages; > int err; > @@ -413,8 +414,11 @@ int __add_pages(int nid, unsigned long pfn, unsigned long nr_pages, > SECTION_ALIGN_UP(pfn + 1) - pfn); > err = sparse_add_section(nid, pfn, cur_nr_pages, altmap, > params->pgmap); > - if (err) > + if (err) { > + __remove_pages(start_pfn, pfn - start_pfn, altmap, > + params->pgmap); > break; > + } > cond_resched(); > } > vmemmap_populate_print_last(); Makes sense and LGTM. Do we have a Fixes: tag? It probably dates back quite a while ... not sure about stable, we never saw this in practice. But if it's easy, we should just do it? (not sure if we ever had __remove_pages be limited to hotunplug support) I'm planning on picking this up and sending it for the next merge window (so not as a hotfix). Looking at this ... x86 does not really expect add_pages to fail: ret = __add_pages(nid, start_pfn, nr_pages, params); WARN_ON_ONCE(ret); That's probably something to clean up as well? -- Cheers, David