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 13A481B4153 for ; Thu, 17 Apr 2025 16:07:29 +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=1744906050; cv=none; b=Dd6qQALQdlfl8aQwEm5VpN+tP0QT+CHA8a8d03+5YBpsQgzNOVfmxVK6zz/BjY2RyEdCupRG3g7JuDox6LG093PUcy1dTSZ19cp0nx30CIkjNaF4CEtfyB5Y+KTW+QLE2Bm32/FbBpPZpYY46VYMF/VAfyzqsJRzxlyBoSJ2EYU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744906050; c=relaxed/simple; bh=Wa7gHZln12dvfA4pOGNKpc1rjCEwjtm8F7ok6Kc7dBY=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=nucXQzALPmCV4jRvTwngzcbtYoN5By4mwVBVEC5PdsxhuIZeb/aXqeuTFPZXaPqbkJZlO0tTGSO1ukId0sTxJ1p47QKmR+i/cfxyXJNXiywALBtcA3fTZXqDHWBijgdoa4Myv8Ie/V/uNymdvcYXOWljdpC2MgL9TAdgCUBbD70= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=E+sGNXaQ; 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="E+sGNXaQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 140D8C4CEE4; Thu, 17 Apr 2025 16:07:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1744906049; bh=Wa7gHZln12dvfA4pOGNKpc1rjCEwjtm8F7ok6Kc7dBY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=E+sGNXaQR7cJzpr5zel8DE7UW9/xQ3Kd0yafK9oAxu1S1dNoCaqATD+q9gCF0913o bhGk7SIbxKkpT11albXqdzXM2nJwqLA0TpjyrruR2uDuQYkfm5X+EiRXniJpbz1pjW h2tOLRtDaMugxe1bZD0tmTPQ6kM14O8yyLBABUw9NmDpV6ENS8kgPZkKnSVEAYhMS0 sGYtcjZ0dfOR6nD269cRKYz6Ks11MR0KzBFmL7+pbQN/D0bTEgP105+o3jjoM0L0zf EBjhk9+cGBBo/ig5D3QCsoPPHOIAl0tq7RYc+xwaWg9xiiB17g2x4HErJqgpzhHw/z fUOHWn9B6C5kw== Date: Thu, 17 Apr 2025 09:07:28 -0700 From: Jakub Kicinski To: Victor Nogueira Cc: netdev@vger.kernel.org, jhs@mojatatu.com, xiyou.wangcong@gmail.com, jiri@resnulli.us, davem@davemloft.net, edumazet@google.com, pabeni@redhat.com, toke@redhat.com, gerrard.tai@starlabs.sg, pctammela@mojatatu.com Subject: Re: [PATCH net v2 0/5] net_sched: Adapt qdiscs for reentrant enqueue cases Message-ID: <20250417090728.5325e724@kernel.org> In-Reply-To: <20250416102427.3219655-1-victor@mojatatu.com> References: <20250416102427.3219655-1-victor@mojatatu.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 16 Apr 2025 07:24:22 -0300 Victor Nogueira wrote: > As described in Gerrard's report [1], there are cases where netem can > make the qdisc enqueue callback reentrant. Some qdiscs (drr, hfsc, ets, > qfq) break whenever the enqueue callback has reentrant behaviour. > This series addresses these issues by adding extra checks that cater for > these reentrant corner cases. This series has passed all relevant test > cases in the TDC suite. Sorry for asking this question a bit late, but reentrant enqueue seems error prone. Is there a clear use case for netem as a child? If so should we also add some sort of "capability" to avoid new qdiscs falling into the same trap, without giving the problem any thought?