From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (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 DEECF1FCC for ; Mon, 17 Jul 2023 06:32:43 +0000 (UTC) Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2AE2CD9; Sun, 16 Jul 2023 23:32:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1689575562; x=1721111562; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=UIvScjBMq2tJ7obc7FO/ZTmBFLS/+sEbi6AjYJ3oqcc=; b=BT/9+IXhbgKgcCBzQy6mYEkMXdirLWUm5Ya6iv46LOb7zqr7u/8Ow33c k3Fu3ZGWAV0R+uFE5IcNxzKiORB9hXy/40hkOPotLGlb0sZAbnLtUxU9P uVpklhfVZkVfbsgfBIN8srS7by6ZZL50whXKWeNGrfL/FAV+Z6kn/OQTr OzbezQAfpc7A3OFquHML5ZyQt04GqzHOMun7PQ3X3ZWTJcJPMJdrUsU9S BaXYtewzNhqRSyIERskt6VYh3alCGMXSMbTXrBTT4UwOFhZ0iabj/dwof VQiace8CR+dHfvhHo1bm8z+I8dOMCIKZSDWw6nM2al1suKn1UBFPTN9bk Q==; X-IronPort-AV: E=McAfee;i="6600,9927,10773"; a="350721120" X-IronPort-AV: E=Sophos;i="6.01,211,1684825200"; d="scan'208";a="350721120" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Jul 2023 23:32:41 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10773"; a="788532240" X-IronPort-AV: E=Sophos;i="6.01,211,1684825200"; d="scan'208";a="788532240" Received: from naamamex-mobl.ger.corp.intel.com (HELO [10.13.12.54]) ([10.13.12.54]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Jul 2023 23:32:36 -0700 Message-ID: <68dcdf3c-226c-9a94-0860-68c6d4b8ca0e@linux.intel.com> Date: Mon, 17 Jul 2023 09:32:33 +0300 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [Intel-wired-lan] [PATCH net v3] igc: Prevent garbled TX queue with XDP ZEROCOPY Content-Language: en-US To: Florian Kauer , Jesse Brandeburg , Tony Nguyen , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Vedang Patel , Maciej Fijalkowski , Jithu Joseph , Andre Guedes , Simon Horman Cc: netdev@vger.kernel.org, kurt@linutronix.de, linux-kernel@vger.kernel.org, intel-wired-lan@lists.osuosl.org References: <20230630120306.8534-1-florian.kauer@linutronix.de> From: "naamax.meir" In-Reply-To: <20230630120306.8534-1-florian.kauer@linutronix.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_EF,NICE_REPLY_A, RCVD_IN_DNSWL_BLOCKED,SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On 6/30/2023 15:03, Florian Kauer wrote: > In normal operation, each populated queue item has > next_to_watch pointing to the last TX desc of the packet, > while each cleaned item has it set to 0. In particular, > next_to_use that points to the next (necessarily clean) > item to use has next_to_watch set to 0. > > When the TX queue is used both by an application using > AF_XDP with ZEROCOPY as well as a second non-XDP application > generating high traffic, the queue pointers can get in > an invalid state where next_to_use points to an item > where next_to_watch is NOT set to 0. > > However, the implementation assumes at several places > that this is never the case, so if it does hold, > bad things happen. In particular, within the loop inside > of igc_clean_tx_irq(), next_to_clean can overtake next_to_use. > Finally, this prevents any further transmission via > this queue and it never gets unblocked or signaled. > Secondly, if the queue is in this garbled state, > the inner loop of igc_clean_tx_ring() will never terminate, > completely hogging a CPU core. > > The reason is that igc_xdp_xmit_zc() reads next_to_use > before acquiring the lock, and writing it back > (potentially unmodified) later. If it got modified > before locking, the outdated next_to_use is written > pointing to an item that was already used elsewhere > (and thus next_to_watch got written). > > Fixes: 9acf59a752d4 ("igc: Enable TX via AF_XDP zero-copy") > Signed-off-by: Florian Kauer > Reviewed-by: Kurt Kanzenbach > Tested-by: Kurt Kanzenbach > Acked-by: Vinicius Costa Gomes > --- > > v2 -> v3: > Resolve merge conflict > > v1 -> v2: > I added some more context for further clarification, > but it is also just how I interpret the code. > Also the typo is fixed and it is reverse christmas again 😉 > > --- > drivers/net/ethernet/intel/igc/igc_main.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) Tested-by: Naama Meir