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 F323A335571; Mon, 16 Mar 2026 16:23:21 +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=1773678202; cv=none; b=FmPQciT9FmKtLl53lKGOTBn7FNgmYXbJ4y83wEnVp0mTLWcysb8t3K6XGx6MEFSjJ9uBRz2Wy1oXoj8eFtg27NhOFSSWW/mqQvP3Cpa9IXGmGDXmkCu+qQdU9NoFyjJK8Iu4DerDepcZBwOOcGjir+2cnO1fdOvlbpk1doijbQA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773678202; c=relaxed/simple; bh=asNjBO76Amhl5nYiIDEn+MotDNaDx0SGtaf4hEltfT8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=HWz/1WGiFVokUHb5exvMJGo5Usm6ljOAFMtfO3LE8XYXZOK6eIQO8uJTxjhLXPNfDIvNh7RhJutJyS6AGfKnwW2ElAwJ1lKNCtdD8DaIeV3UD00EPc2PE2oQAMzc+YkiXaK6763PSlUwxALgzOpBaVlSPKCyu7QPqYQBhNxKW38= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gd49k6HM; 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="gd49k6HM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6BECEC19425; Mon, 16 Mar 2026 16:23:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773678201; bh=asNjBO76Amhl5nYiIDEn+MotDNaDx0SGtaf4hEltfT8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=gd49k6HM86HJOavNiYPbzwo4gVsgs2BU12luvHrMFjjNLPoEdN4VrwtaGEvbYPNNS mY7JgPf8AleDXMyDWW7MZmU9dNtY1LrQ96+gACmj1foWn+Ilo/qHNT+UNO0w27AN1i d+pJ1x7r1tmFsVBYGDDU6nBC83htBoG5zpsK3vU349J2SYn56M6puR8VXu0hUY0wLu cVoF91ZyTJEaBuibZr48VTVBjX5HD+bd8ttJb+1B5lEcXXNQKISLPAi3hkmzXba9wK vNMbB5hKG+Rt5vtBXhQKYlYYdkVfebwPXWkLTrE8Y9v3s4a/k7E5EI51OcPxnOFfLG jAtePRbYx+ilw== Message-ID: <6ada27e1-8f85-4b85-8c25-bc9207b2624d@kernel.org> Date: Mon, 16 Mar 2026 17:23:17 +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 PATCH v3 0/2] Fix storing in XArray check_split tests To: Ackerley Tng , willy@infradead.org, akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: michael.roth@amd.com, dev.jain@arm.com, vannapurve@google.com, Zi Yan References: 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 2/23/26 08:34, Ackerley Tng wrote: > Hi, > > I hit an assertion while making some modifications to > lib/test_xarray.c [1] and I believe this is the fix. > > In check_split, the tests split the XArray node and then store values > after the split to verify that splitting worked. While storing and > retrieval works as expected, the node's metadata, specifically > node->nr_values, is not updated correctly. > > This led to the assertion being hit in [1], since the storing process > did not increment node->nr_values sufficiently, while the erasing > process assumed the fully-incremented node->nr_values state. > > Would like to check my understanding on these: > > 1. In the multi-index xarray world, is node->nr_values definitely the > total number of values *and siblings* in the node? > > 2. IIUC xas_store() has significantly different behavior when entry is > NULL vs non-NULL: when entry is NULL, xas_store() does not make > assumptions on the number of siblings and erases all the way till > the next non-sibling entry. This sounds fair to me, but it's also > kind of surprising that it is differently handled when entry is > non-NULL, where xas_store() respects xas->xa_sibs. > > 3. If xas_store() is dependent on its caller to set up xas correctly > (also sounds fair), then there are places where xas_store() is > used, like replace_page_cache_folio() or > migrate_huge_page_move_mapping(), where xas is set up assuming 0 > order pages. Are those buggy? Zi, do you have any familiarity with that code and could help? Thanks! -- Cheers, David