From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E701EC433F5 for ; Fri, 18 Mar 2022 19:04:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240292AbiCRTGD (ORCPT ); Fri, 18 Mar 2022 15:06:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54582 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233464AbiCRTGA (ORCPT ); Fri, 18 Mar 2022 15:06:00 -0400 Received: from mail-pf1-x429.google.com (mail-pf1-x429.google.com [IPv6:2607:f8b0:4864:20::429]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EF81812E76E; Fri, 18 Mar 2022 12:04:40 -0700 (PDT) Received: by mail-pf1-x429.google.com with SMTP id a5so10285740pfv.2; Fri, 18 Mar 2022 12:04:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=xM89dBLgHUjq97tcZvokpl3g97A4c94XFB2GzNk5daY=; b=ew4IiMQ8LKtfQHCC4Bn86a8CTNsF9Yvl1PYpFN7NXvEBeBNxmCmbPV6TTumQa4srqY SBpv8qD+9w+UVdpwVmPzPkn9R1A83d2AJO2SW3+74O1Ogd8Q7k0599nUG4csNL5qXbhW H/XO9OWumsd6RUy4OwzkFq1f1xrTeYdi7CQsGgTZFLQa5IcTCYYNX12iUMAUzY5iApXX RptzrcDE5mPlG3oPXMMibc7nqQ86KnNbUpL7YQfvpvPOmRCjt4D2umelF35qNpJy1OOM chStPclo/4rwWODufXs0LA1WspD3lWAd/eMVviq9iB6dXcsd4TiiOgt4fzFHsMTxuweO Op4Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=xM89dBLgHUjq97tcZvokpl3g97A4c94XFB2GzNk5daY=; b=iGsdKqpLEZeEI8wZCVd/hpn/daVYcyXbjMd8tNnncRb93o0NXJ2AueaPzigPYAoNas Hr9iOLUwQyh+y8atyE7+ghWSZc4DdT+DzNCUbTyYgkudmfPgebIccO3yMWClm4dJkQE8 HakLsqHKlvK6jacdqaRCvKq8ZPkNUqy7PwQhVSdLMD6eNoaDHk+tpZ/SJ//l/6d8waVM V0KLQUcNUDA9rM72MfZcrFiZkXOsY0+LxukTFY9paiqxMdZ/7iS2IB7amh76IxsxRXs7 GukoYHmV6raTYUTfoZBtoh8Alrdji2LVuvRNqhHmTEtetfLXUPRPbx8bZ9PKMgmwJrsT APog== X-Gm-Message-State: AOAM530j11sQF85JwemkYDfeNuFxSfdHwmCg52mP54tGrcspfB/lOjPU QZeqKdu6lr+aDOghKru4O4s= X-Google-Smtp-Source: ABdhPJyq3BvxkXs1FefMxiG5jjm/IXVFVwKoPwbMJWV4VWmFd5K6ge47aHJCCA9T/oHnmBhvMayrxw== X-Received: by 2002:a05:6a00:14c9:b0:4f7:763b:2efd with SMTP id w9-20020a056a0014c900b004f7763b2efdmr11712823pfu.55.1647630280402; Fri, 18 Mar 2022 12:04:40 -0700 (PDT) Received: from [10.67.48.245] ([192.19.223.252]) by smtp.googlemail.com with ESMTPSA id q21-20020a63e215000000b00373efe2cbcbsm8026080pgh.80.2022.03.18.12.04.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 18 Mar 2022 12:04:39 -0700 (PDT) Subject: Re: [PATCH] net: bcmgenet: Use stronger register read/writes to assure ordering To: Jeremy Linton , netdev@vger.kernel.org Cc: opendmb@gmail.com, f.fainelli@gmail.com, davem@davemloft.net, kuba@kernel.org, bcm-kernel-feedback-list@broadcom.com, linux-kernel@vger.kernel.org, Peter Robinson References: <20220310045358.224350-1-jeremy.linton@arm.com> From: Florian Fainelli Message-ID: <0465ecd0-0cd7-1376-51bf-38aa385c128a@gmail.com> Date: Fri, 18 Mar 2022 12:04:34 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: <20220310045358.224350-1-jeremy.linton@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/9/22 8:53 PM, Jeremy Linton wrote: > GCC12 appears to be much smarter about its dependency tracking and is > aware that the relaxed variants are just normal loads and stores and > this is causing problems like: > > [ 210.074549] ------------[ cut here ]------------ > [ 210.079223] NETDEV WATCHDOG: enabcm6e4ei0 (bcmgenet): transmit queue 1 timed out > [ 210.086717] WARNING: CPU: 1 PID: 0 at net/sched/sch_generic.c:529 dev_watchdog+0x234/0x240 > [ 210.095044] Modules linked in: genet(E) nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat] > [ 210.146561] ACPI CPPC: PCC check channel failed for ss: 0. ret=-110 > [ 210.146927] CPU: 1 PID: 0 Comm: swapper/1 Tainted: G E 5.17.0-rc7G12+ #58 > [ 210.153226] CPPC Cpufreq:cppc_scale_freq_workfn: failed to read perf counters > [ 210.161349] Hardware name: Raspberry Pi Foundation Raspberry Pi 4 Model B/Raspberry Pi 4 Model B, BIOS EDK2-DEV 02/08/2022 > [ 210.161353] pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) > [ 210.161358] pc : dev_watchdog+0x234/0x240 > [ 210.161364] lr : dev_watchdog+0x234/0x240 > [ 210.161368] sp : ffff8000080a3a40 > [ 210.161370] x29: ffff8000080a3a40 x28: ffffcd425af87000 x27: ffff8000080a3b20 > [ 210.205150] x26: ffffcd425aa00000 x25: 0000000000000001 x24: ffffcd425af8ec08 > [ 210.212321] x23: 0000000000000100 x22: ffffcd425af87000 x21: ffff55b142688000 > [ 210.219491] x20: 0000000000000001 x19: ffff55b1426884c8 x18: ffffffffffffffff > [ 210.226661] x17: 64656d6974203120 x16: 0000000000000001 x15: 6d736e617274203a > [ 210.233831] x14: 2974656e65676d63 x13: ffffcd4259c300d8 x12: ffffcd425b07d5f0 > [ 210.241001] x11: 00000000ffffffff x10: ffffcd425b07d5f0 x9 : ffffcd4258bdad9c > [ 210.248171] x8 : 00000000ffffdfff x7 : 000000000000003f x6 : 0000000000000000 > [ 210.255341] x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000001000 > [ 210.262511] x2 : 0000000000001000 x1 : 0000000000000005 x0 : 0000000000000044 > [ 210.269682] Call trace: > [ 210.272133] dev_watchdog+0x234/0x240 > [ 210.275811] call_timer_fn+0x3c/0x15c > [ 210.279489] __run_timers.part.0+0x288/0x310 > [ 210.283777] run_timer_softirq+0x48/0x80 > [ 210.287716] __do_softirq+0x128/0x360 > [ 210.291392] __irq_exit_rcu+0x138/0x140 > [ 210.295243] irq_exit_rcu+0x1c/0x30 > [ 210.298745] el1_interrupt+0x38/0x54 > [ 210.302334] el1h_64_irq_handler+0x18/0x24 > [ 210.306445] el1h_64_irq+0x7c/0x80 > [ 210.309857] arch_cpu_idle+0x18/0x2c > [ 210.313445] default_idle_call+0x4c/0x140 > [ 210.317470] cpuidle_idle_call+0x14c/0x1a0 > [ 210.321584] do_idle+0xb0/0x100 > [ 210.324737] cpu_startup_entry+0x30/0x8c > [ 210.328675] secondary_start_kernel+0xe4/0x110 > [ 210.333138] __secondary_switched+0x94/0x98 > > The assumption when these were relaxed seems to be that device memory > would be mapped non reordering, and that other constructs > (spinlocks/etc) would provide the barriers to assure that packet data > and in memory rings/queues were ordered with respect to device > register reads/writes. This itself seems a bit sketchy, but the real > problem with GCC12 is that it is moving the actual reads/writes around > at will as though they were independent operations when in truth they > are not, but the compiler can't know that. When looking at the > assembly dumps for many of these routines its possible to see very > clean, but not strictly in program order operations occurring as the > compiler would be free to do if these weren't actually register > reads/write operations. > > Its possible to suppress the timeout with a liberal bit of dma_mb()'s > sprinkled around but the device still seems unable to reliably > send/receive data. A better plan is to use the safer readl/writel > everywhere. > > Since this partially reverts an older commit, which notes the use of > the relaxed variants for performance reasons. I would suggest that > any performance problems with this commit are targeted at relaxing only > the performance critical code paths after assuring proper barriers. > > Fixes: 69d2ea9c79898 ("net: bcmgenet: Use correct I/O accessors") > Reported-by: Peter Robinson > Signed-off-by: Jeremy Linton Acked-by: Florian Fainelli -- Florian