From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-132.freemail.mail.aliyun.com (out30-132.freemail.mail.aliyun.com [115.124.30.132]) (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 528281607A4; Fri, 26 Dec 2025 14:22:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.132 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766758939; cv=none; b=kuGY6qfrgv/WMyqXzOlFhMf7YHeZMuL38bGUxr5wMcMXD4j7zqJ3bZfTjW8z6TYre0GMl/JsUmc2eODey+i0lItD1pFOp38uxpgDv17x6IoDD8LubfNMhNr+IdJ897aB67N5iboouZ3f2e7TDTr5vtPx/nPuPS33xgL92SV/S+c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766758939; c=relaxed/simple; bh=ff0ntZw7Gi4F++vaU/E8El4jhspXYH4arAN2FTm/6Dc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=EcpVYIPTjyZItOhXDUluxLxFAfWbtuHbsFcujI+qdT+t2SNdQJSPsVrgHDXNdEIzAni6CG9N/aA/JEsFCstwoF8uZJ7dNaznzhZR4VLrW2ncZrFH12+vjfD8Ys6s7sFRLJM8hSA9J8SXRnp7gO6r3Dqjfmnwt1+3bX26VVTpA0U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=j4tb5Ztz; arc=none smtp.client-ip=115.124.30.132 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="j4tb5Ztz" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1766758932; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=9xf2HFCC6Ziw68Fb8elQMRwG16Hpctrj/C6ytUD938o=; b=j4tb5Ztzcn1/uId5tzxEvo3r1QVyacbIVGxkDX7K1yBQmYg3Hsnzzi2pIn2FnbMfJWO/mFhYSfm+//2SNmow431+cCx09bKKty+7EEgdgp4+lwR21jOlDVRWW0xdLw8TU2Byl2kaFlJvZlHQvEvaETDLZSV7F2WSkUedAwRvABQ= Received: from 30.69.38.206(mailfrom:hsiangkao@linux.alibaba.com fp:SMTPD_---0WvhnUlN_1766758923 cluster:ay36) by smtp.aliyun-inc.com; Fri, 26 Dec 2025 22:22:11 +0800 Message-ID: Date: Fri, 26 Dec 2025 22:22:01 +0800 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: [REGRESSION] erofs: new file-backed stacking limit breaks container overlay use case in 6.12.63 To: =?UTF-8?B?QWxla3PDqWkgTmFpZMOpbm92?= , stable@vger.kernel.org Cc: linux-erofs@lists.ozlabs.org, linux-kernel@vger.kernel.org, xiang@kernel.org, Amir Goldstein , Christian Brauner References: From: Gao Xiang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Hi Alekséi, On 2025/12/26 20:17, Alekséi Naidénov wrote: > Hello, > > I am reporting a regression in the 6.12 stable series related to EROFS > file-backed mounts. > > After updating from Linux 6.12.62 to 6.12.63, a previously working setup > using OSTree-backed composefs mounts as Podman rootfs no longer works. > > The regression appears to be caused by the following commit: > > 34447aeedbaea8f9aad3da5b07030a1c0e124639 ("erofs: limit the level of fs > stacking for file-backed mounts") > (backport of upstream commit d53cd891f0e4311889349fff3a784dc552f814b9) > > ## Setup description > > We use OSTree to materialize filesystem trees, which are mounted via > composefs (EROFS + overlayfs) as a read-only filesystem. This mounted > composefs tree is then used as a Podman rootfs, with Podman mounting a > writable overlayfs on top for each container. > > This setup worked correctly on Linux 6.12.62 and earlier. The following issue just tracks this: https://github.com/coreos/fedora-coreos-tracker/issues/2087 I don't think more information is needed, but I really think the EROFS commit is needed to avoid kernel stack overflow due to nested fses. > > In short, the stacking looks like: > > EROFS (file-backed) > -> composefs (EROFS + overlayfs with ostree repo as datadir, read-only) > -> Podman rootfs overlays (RW upperdir) > > There is no recursive or self-stacking of EROFS. Yes, but there are two overlayfs + one file-backed EROFS already, and it exceeds FILESYSTEM_MAX_STACK_DEPTH. That is overlayfs refuses to mount the nested fses. Thanks, Gao Xiang