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 AED1A23D6 for ; Fri, 13 Oct 2023 07:21:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="pzOa5h6G" Received: from mail-vs1-xe31.google.com (mail-vs1-xe31.google.com [IPv6:2607:f8b0:4864:20::e31]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 33C81B8 for ; Fri, 13 Oct 2023 00:21:43 -0700 (PDT) Received: by mail-vs1-xe31.google.com with SMTP id ada2fe7eead31-4577c1259c6so832826137.3 for ; Fri, 13 Oct 2023 00:21:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1697181702; x=1697786502; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=j8abOWZApChL1PiO6AUXU9AraOSNbvy4h27WNIKy1U8=; b=pzOa5h6G+lnHpaZY8t2znU2TwS1KthQ+/97ZXN8Hs1rk4xj5125RaPKW9r3HX8Cfbm sfenu3ex8G3pN8nt+FdP+frvctpew/iUOSAhG7K0Ewx1GLmABGyDxrPQLyc8skJPSbye jmx7e3nximNAGdxz5Nevpnfr0ZelAdEny8NJf19YAEmMCU4CXuzheNkHnkkLyN3ao544 3bBjWVnnMxLz4ummO8akiR9xyvqh70tSVJS9NegW5xCHCKCboXITnDuds/eum5+HnZwj 5MimExDuLNVQIOmVtc5JhREEVNNHRCdOZHM0dDx6YLNUb0AYFHYl6T3n4pOti/IooJIS XEAQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1697181702; x=1697786502; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=j8abOWZApChL1PiO6AUXU9AraOSNbvy4h27WNIKy1U8=; b=MVNRmZLuErQZi+fRjUzUWDU5iXI9EbSWj17xmsEmd5wWVcXWtWH5TLO4FKtQTF2ktJ raanoniV5tImf3icuKDjW/hm2dgHhONNC6VhpYJ0Kyg1Qt1dXQO97S6r1JpIruJEgkbW Y+yl3qPFEf3n2iFMbghy5H5djk2D8RGo5JcxICE8jfyR08SdACnKQpCBnIbowmlNad2p gAIoc63z7ZTSMZse7T8MoSFjpkgq7RBrIad2h6TMfwUhY9T6H1AB/td9hmyh2acs7ucA 6q6X+gz2bgbg4kNHi/V7Up3UX5MjHW1bqFyt3QkyGvfLbo2SMfZiO6B8uL6eSerFTA+z 5M/w== X-Gm-Message-State: AOJu0Yw8yjOOpaVC/pfDps32YGXRzB+829hl1/mUMrVmBEvLfhQlhJtr UA/iFS839FsIRHkweiN9fIB/gn2OYbiVsdOSnb/Glg== X-Google-Smtp-Source: AGHT+IGBIJ1+IYHOty4ow0VY+MIqV07mOzDrS2bzkJ5Er9WYHkkAIWiaTji+gKQOJegDt6nOcK6hqcbAv+JhMs9BdEc= X-Received: by 2002:a67:fd49:0:b0:452:5a4c:7278 with SMTP id g9-20020a67fd49000000b004525a4c7278mr20272141vsr.20.1697181701700; Fri, 13 Oct 2023 00:21:41 -0700 (PDT) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20230927184158.243575-1-mirsad.todorovac@alu.unizg.hr> <0a201a6f-90dd-403c-97d0-94372be1e3e6@gmail.com> <250140d1-d592-45f4-aa27-691c1d68a528@alu.unizg.hr> In-Reply-To: <250140d1-d592-45f4-aa27-691c1d68a528@alu.unizg.hr> From: Marco Elver Date: Fri, 13 Oct 2023 09:21:05 +0200 Message-ID: Subject: Re: [PATCH RFC v1 1/3] r8169: fix the KCSAN reported data-race in rtl_tx() while reading tp->cur_tx To: Mirsad Goran Todorovac Cc: Heiner Kallweit , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, nic_swsd@realtek.com, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-17.6 required=5.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, ENV_AND_HDR_SPF_MATCH,RCVD_IN_DNSWL_BLOCKED,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL,USER_IN_DEF_SPF_WL 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 Fri, 13 Oct 2023 at 07:01, Mirsad Goran Todorovac wrote: > > On 9/28/2023 8:02 AM, Marco Elver wrote: > > On Wed, 27 Sept 2023 at 21:52, Heiner Kallweit w= rote: > >> > >> On 27.09.2023 20:41, Mirsad Goran Todorovac wrote: > >>> KCSAN reported the following data-race: > >>> > >>> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > >>> BUG: KCSAN: data-race in rtl8169_poll [r8169] / rtl8169_start_xmit [r= 8169] > >>> > >>> write (marked) to 0xffff888102474b74 of 4 bytes by task 5358 on cpu 2= 9: > >>> rtl8169_start_xmit (drivers/net/ethernet/realtek/r8169_main.c:4254) r= 8169 > >>> dev_hard_start_xmit (./include/linux/netdevice.h:4889 ./include/linux= /netdevice.h:4903 net/core/dev.c:3544 net/core/dev.c:3560) > >>> sch_direct_xmit (net/sched/sch_generic.c:342) > >>> __dev_queue_xmit (net/core/dev.c:3817 net/core/dev.c:4306) > >>> ip_finish_output2 (./include/linux/netdevice.h:3082 ./include/net/nei= ghbour.h:526 ./include/net/neighbour.h:540 net/ipv4/ip_output.c:233) > >>> __ip_finish_output (net/ipv4/ip_output.c:311 net/ipv4/ip_output.c:293= ) > >>> ip_finish_output (net/ipv4/ip_output.c:328) > >>> ip_output (net/ipv4/ip_output.c:435) > >>> ip_send_skb (./include/net/dst.h:458 net/ipv4/ip_output.c:127 net/ipv= 4/ip_output.c:1486) > >>> udp_send_skb (net/ipv4/udp.c:963) > >>> udp_sendmsg (net/ipv4/udp.c:1246) > >>> inet_sendmsg (net/ipv4/af_inet.c:840 (discriminator 4)) > >>> sock_sendmsg (net/socket.c:730 net/socket.c:753) > >>> __sys_sendto (net/socket.c:2177) > >>> __x64_sys_sendto (net/socket.c:2185) > >>> do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80) > >>> entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120) > >>> > >>> read to 0xffff888102474b74 of 4 bytes by interrupt on cpu 21: > >>> rtl8169_poll (drivers/net/ethernet/realtek/r8169_main.c:4397 drivers/= net/ethernet/realtek/r8169_main.c:4581) r8169 > >>> __napi_poll (net/core/dev.c:6527) > >>> net_rx_action (net/core/dev.c:6596 net/core/dev.c:6727) > >>> __do_softirq (kernel/softirq.c:553) > >>> __irq_exit_rcu (kernel/softirq.c:427 kernel/softirq.c:632) > >>> irq_exit_rcu (kernel/softirq.c:647) > >>> common_interrupt (arch/x86/kernel/irq.c:247 (discriminator 14)) > >>> asm_common_interrupt (./arch/x86/include/asm/idtentry.h:636) > >>> cpuidle_enter_state (drivers/cpuidle/cpuidle.c:291) > >>> cpuidle_enter (drivers/cpuidle/cpuidle.c:390) > >>> call_cpuidle (kernel/sched/idle.c:135) > >>> do_idle (kernel/sched/idle.c:219 kernel/sched/idle.c:282) > >>> cpu_startup_entry (kernel/sched/idle.c:378 (discriminator 1)) > >>> start_secondary (arch/x86/kernel/smpboot.c:210 arch/x86/kernel/smpboo= t.c:294) > >>> secondary_startup_64_no_verify (arch/x86/kernel/head_64.S:433) > >>> > >>> value changed: 0x002f4815 -> 0x002f4816 > >>> > >>> Reported by Kernel Concurrency Sanitizer on: > >>> CPU: 21 PID: 0 Comm: swapper/21 Tainted: G L 6.6.0-rc= 2-kcsan-00143-gb5cbe7c00aa0 #41 > >>> Hardware name: ASRock X670E PG Lightning/X670E PG Lightning, BIOS 1.2= 1 04/26/2023 > >>> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > >>> > >>> The write side of drivers/net/ethernet/realtek/r8169_main.c is: > >>> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > >>> 4251 /* rtl_tx needs to see descriptor changes before upd= ated tp->cur_tx */ > >>> 4252 smp_wmb(); > >>> 4253 > >>> =E2=86=92 4254 WRITE_ONCE(tp->cur_tx, tp->cur_tx + frags + = 1); > >>> 4255 > >>> 4256 stop_queue =3D !netif_subqueue_maybe_stop(dev, 0, rt= l_tx_slots_avail(tp), > >>> 4257 R8169_TX_STO= P_THRS, > >>> 4258 R8169_TX_STA= RT_THRS); > >>> > >>> The read side is the function rtl_tx(): > >>> > >>> 4355 static void rtl_tx(struct net_device *dev, struct rtl8169_pr= ivate *tp, > >>> 4356 int budget) > >>> 4357 { > >>> 4358 unsigned int dirty_tx, bytes_compl =3D 0, pkts_compl= =3D 0; > >>> 4359 struct sk_buff *skb; > >>> 4360 > >>> 4361 dirty_tx =3D tp->dirty_tx; > >>> 4362 > >>> 4363 while (READ_ONCE(tp->cur_tx) !=3D dirty_tx) { > >>> 4364 unsigned int entry =3D dirty_tx % NUM_TX_DES= C; > >>> 4365 u32 status; > >>> 4366 > >>> 4367 status =3D le32_to_cpu(tp->TxDescArray[entry= ].opts1); > >>> 4368 if (status & DescOwn) > >>> 4369 break; > >>> 4370 > >>> 4371 skb =3D tp->tx_skb[entry].skb; > >>> 4372 rtl8169_unmap_tx_skb(tp, entry); > >>> 4373 > >>> 4374 if (skb) { > >>> 4375 pkts_compl++; > >>> 4376 bytes_compl +=3D skb->len; > >>> 4377 napi_consume_skb(skb, budget); > >>> 4378 } > >>> 4379 dirty_tx++; > >>> 4380 } > >>> 4381 > >>> 4382 if (tp->dirty_tx !=3D dirty_tx) { > >>> 4383 dev_sw_netstats_tx_add(dev, pkts_compl, byte= s_compl); > >>> 4384 WRITE_ONCE(tp->dirty_tx, dirty_tx); > >>> 4385 > >>> 4386 netif_subqueue_completed_wake(dev, 0, pkts_c= ompl, bytes_compl, > >>> 4387 rtl_tx_slots_a= vail(tp), > >>> 4388 R8169_TX_START= _THRS); > >>> 4389 /* > >>> 4390 * 8168 hack: TxPoll requests are lost when = the Tx packets are > >>> 4391 * too close. Let's kick an extra TxPoll req= uest when a burst > >>> 4392 * of start_xmit activity is detected (if it= is not detected, > >>> 4393 * it is slow enough). -- FR > >>> 4394 * If skb is NULL then we come here again on= ce a tx irq is > >>> 4395 * triggered after the last fragment is mark= ed transmitted. > >>> 4396 */ > >>> =E2=86=92 4397 if (tp->cur_tx !=3D dirty_tx && skb) > >>> 4398 rtl8169_doorbell(tp); > >>> 4399 } > >>> 4400 } > >>> > >>> Obviously from the code, an earlier detected data-race for tp->cur_tx= was fixed in the > >>> line 4363: > >>> > >>> 4363 while (READ_ONCE(tp->cur_tx) !=3D dirty_tx) { > >>> > >>> but the same solution is required for protecting the other access to = tp->cur_tx: > >>> > >>> =E2=86=92 4397 if (READ_ONCE(tp->cur_tx) !=3D dirty= _tx && skb) > >>> 4398 rtl8169_doorbell(tp); > >>> > >>> The write in the line 4254 is protected with WRITE_ONCE(), but the re= ad in the line 4397 > >>> might have suffered read tearing under some compiler optimisations. > >>> > >>> The fix eliminated the KCSAN data-race report for this bug. > >>> > >>> It is yet to be evaluated what happens if tp->cur_tx changes between = the test in line 4363 > >>> and line 4397. This test should certainly not be cached by the compil= er in some register > >>> for such a long time, while asynchronous writes to tp->cur_tx might h= ave occurred in line > >>> 4254 in the meantime. > >>> > >> > >> netif_subqueue_completed_wake() has barriers ensuring that no cached v= alue for tp->cur_tx > >> is used in line 4397. I'm not aware of any reported issues with an obv= ious link to the > >> potentential issue you describe. > >> I don't have a strong opinion on these patches. They shouldn't hurt, a= nd if they make > >> KCSAN happy, why not. > > > > Barries don't protect unmarked accesses from being miscompiled. So the > > use of barriers and marked accesses like READ_ONCE() is correct: > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree= /tools/memory-model/Documentation/access-marking.txt > > That said, actually encountering a miscompilation depends on > > architecture and compiler. Using the right marked accesses just > > ensures things don't suddenly break because the compiler decided to be > > a little more clever. > > > >>> Fixes: 94d8a98e6235c ("r8169: reduce number of workaround doorbell ri= ngs") > >>> Cc: Heiner Kallweit > >>> Cc: nic_swsd@realtek.com > >>> Cc: "David S. Miller" > >>> Cc: Eric Dumazet > >>> Cc: Jakub Kicinski > >>> Cc: Paolo Abeni > >>> Cc: Marco Elver > >>> Cc: netdev@vger.kernel.org > >>> Link: https://lore.kernel.org/lkml/dc7fc8fa-4ea4-e9a9-30a6-7c83e6b531= 88@alu.unizg.hr/ > >>> Signed-off-by: Mirsad Goran Todorovac > > > > Acked-by: Marco Elver > > Hi, Marco, > > Does this Acked-by: cover all of the [123]/3 in the patch series? Technically, no. (Only if this was the cover lettter i.e. 0/n) Send the non-RFC separately and I'll ack them.