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 D5388347DD; Sun, 22 Jun 2025 09:10:51 +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=1750583451; cv=none; b=uiHnUwRWHs0wdrJo64mzsdL+m+Qj7yHb2DIQdb3aDi4LIVl5HELzBmIY+7TmE7Bup0dtZkPxCb1AvQRsVpJdw5Ra+aImXkamsET19cgeD8AqBOHGmVJn0pCtry/l15kiuRqaPxPTXe+axtm6YPNvdmoIvAf3XnLTcT+AWPGZqDc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750583451; c=relaxed/simple; bh=zVuqY37en/DKxiVJYxlp6D3HbV0uNfcMQBfBnwgXRPc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ntYpcqMfXPQU9bxJ2JKi1S0Wou4dlZluo3LalS220UXqa0R9RhY4D4plO5HNJojkh9Rw/DZpToXGtV1MUkNCoj191wL2Ev+wTGQIDodJdJ2DURSP5rq+OnogKzzeO7NiLSXMPyHoOkDw1xzxa1naHyj4cvpW0+yzDLrwZbdn7lg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=bdrUVuQ0; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="bdrUVuQ0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 53EB1C4CEE3; Sun, 22 Jun 2025 09:10:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1750583451; bh=zVuqY37en/DKxiVJYxlp6D3HbV0uNfcMQBfBnwgXRPc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=bdrUVuQ0WU0qMhIbKMWuW9/d24ydilDNRV5S1KgGD9JFRWt2uomXBFSy7se9/8M0G ffnWRE1fDhbJ85wIhGxQR1Ksi6yBlXK4uBm5CfmwcWiab78PV/LWSpjWDYO1/96F4O pxUuNSxCpFkPfAF8qC+y8JNuzSsVfNb5Uwtqd5XQ= Date: Sun, 22 Jun 2025 11:10:49 +0200 From: Greg KH To: Willem de Bruijn Cc: Brett Sheffield , Brett Sheffield , stable@vger.kernel.org, regressions@lists.linux.dev Subject: Re: 6.12.y longterm regression - IPv6 UDP packet fragmentation Message-ID: <2025062212-erasable-riches-d3eb@gregkh> References: <2025061745-calamari-voyage-d27a@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Jun 17, 2025 at 02:25:02PM -0400, Willem de Bruijn wrote: > On Tue, Jun 17, 2025 at 1:29 PM Brett Sheffield wrote: > > > > Hi Greg, > > > > On 2025-06-17 15:47, Greg KH wrote: > > > On Wed, Jun 11, 2025 at 01:04:29PM +0200, Brett Sheffield wrote: > > > > Longterm kernel 6.12.y backports commit: > > > > > > > > - a18dfa9925b9ef6107ea3aa5814ca3c704d34a8a "ipv6: save dontfrag in cork" > > > > > > It's also in older kernels: > > > 5.10.238 > > > 5.15.185 > > > 6.1.141 > > > 6.6.93 > > > > > > > but does not backport these related commits: > > > > > > > > - 54580ccdd8a9c6821fd6f72171d435480867e4c3 "ipv6: remove leftover ip6 cookie initializer" > > > > - 096208592b09c2f5fc0c1a174694efa41c04209d "ipv6: replace ipcm6_init calls with ipcm6_init_sk" > > > > > > > > This causes a regression when sending IPv6 UDP packets by preventing > > > > fragmentation and instead returning EMSGSIZE. I have attached a program which > > > > demonstrates the issue. > > Thanks for the analysis. I had received a report and was looking into > it, but had not yet figured out this root cause. > > > > > > > Should we backport thse two to all of the other branches as well? > > > > I have confirmed the regression is present in all of those older kernels (except > > 5.15.185 as that didn't boot on my test hardware - will look at that later). > > > > The patch appears to have been autoselected for applying to the stable tree: > > > > https://lore.kernel.org/all/?q=a18dfa9925b9ef6107ea3aa5814ca3c704d34a8a > > > > The patch follows on from a whole series of patches by Willem de Bruijn (CC), the > > rest of which were not applied. > > > > Unless there is a good reason for applying this patch in isolation, the quickest > > fix is simply to revert that commit in stable and this fixes the regression. > > > > Alternatives are: > > > > 1) apply a small fix for the regression (patch attached). This leaves a footgun > > if you later decide to backport more of the series. > > > > 2) to backport and test the whole series of patches. See merge commit > > aefd232de5eb2e77e3fc58c56486c7fe7426a228 > > > > 3) In the case of 6.12.33, the two patches I referenced apply cleanly and are enough > > to fix the problem. There are conflicts on the other branches. > > > > Unless there is a specific reason to have backported > > a18dfa9925b9ef6107ea3aa5814ca3c704d34a8a to stable I'd suggest just reverting > > it. > > FWIW, I did not originally intend for these changes to make it to stable. > > The simplest short term solution is to revert this patch out of the > stable trees. But long term that may give more conflicts as later > patches need to be backported? Not sure what is wiser in such cases. For now, I've applied the above 2 to the 6.12.y tree. They do not apply any older. If I should drop the change from the older stable trees, please let me know. thanks, greg k-h