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[2620:137:e000::3:4]) by mx.google.com with ESMTPS id b15-20020a170903228f00b001c611ca886bsi13702919plh.478.2023.09.28.09.48.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 Sep 2023 09:48:30 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:4 as permitted sender) client-ip=2620:137:e000::3:4; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20230601 header.b=TxN++rnX; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:4 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com Received: from out1.vger.email (depot.vger.email [IPv6:2620:137:e000::3:0]) by howler.vger.email (Postfix) with ESMTP id C18EF8374E5E; Wed, 27 Sep 2023 23:03:57 -0700 (PDT) X-Virus-Status: Clean X-Virus-Scanned: clamav-milter 0.103.10 at howler.vger.email Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230223AbjI1GDn (ORCPT + 99 others); Thu, 28 Sep 2023 02:03:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39322 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230205AbjI1GDk (ORCPT ); Thu, 28 Sep 2023 02:03:40 -0400 Received: from mail-lf1-x129.google.com (mail-lf1-x129.google.com [IPv6:2a00:1450:4864:20::129]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E3E009F for ; Wed, 27 Sep 2023 23:03:37 -0700 (PDT) Received: by mail-lf1-x129.google.com with SMTP id 2adb3069b0e04-50336768615so21395199e87.0 for ; Wed, 27 Sep 2023 23:03:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1695881016; x=1696485816; 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=7JTXwSgZvIedjVBLF/u7wxA0QR3Df5ehqpCs3rBkC+E=; b=TxN++rnXPMD/FF1r0MHzHHCT7vUzxWrHricbgADluxJbTkaVu/bxkizXhWIdfz5809 Lfks+ecpcX2LKUhWBruJtOOtDyviRFh2bx/p3CrZ34E/seslVI9HNfoH9FNbyheUrJdq GvppFX3/+cBu4lPHFS0SRoO10y10lhs6u4amCtoYO1HyH29a8kxHbwhe5ZSgv0WAq7sT WLmrJ5xm3HbVAfo6Kur0DMyVVqqWhTqWjiWwqoIAUKlHW33tJCLx4HnjK44KBPFgPA7d i420ZX1ddETawTMfHrCh9JHM5tm/NT6Nz/OZkj4L7lkln339Vz8L5GRDpFVn1nD5KOZl Xu3A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1695881016; x=1696485816; 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=7JTXwSgZvIedjVBLF/u7wxA0QR3Df5ehqpCs3rBkC+E=; b=pXicrLM7nSmId9vFxjoTsNhjAb4PIWx0VfVvTQi6w6Xj65BNeqto9N6B7Bpfcr1oAw pIg/nwAnQlpvYjjpg4Ye3xcidU0Q/O9l6cLC5BBvOm2MPuYlzrEwtc9/3KOU2k72lQqU WHbgdjKzHrxh6NEPy7P/hSzQUyXEKGeuzptTqa7oYrLvsG6v2LTNtnf24skalYCfznk2 ufBerCr3eGgP1EGnr5ENpIzFgOSYqby6lgAtTR31xdeE5VM7ODXQv8mdHjSu06ToVnOU iRextjp9rFOKVnbWOTQlrqwFoefQLKuOM+F0Yv0DLUUTmClETjE1briovk1q3EOxxgAw eDpQ== X-Gm-Message-State: AOJu0YyX3A9/Y8KPI//bxH/rNQQ/laKHHALTqJX+82VvYQQYKhp+Q8hK /DD9xshNQOvHtxu71RBVdSQG2XDLDEXwJI/IgXAt4A== X-Received: by 2002:ac2:4e81:0:b0:500:771f:4887 with SMTP id o1-20020ac24e81000000b00500771f4887mr224008lfr.55.1695881015922; Wed, 27 Sep 2023 23:03:35 -0700 (PDT) MIME-Version: 1.0 References: <20230927184158.243575-1-mirsad.todorovac@alu.unizg.hr> <0a201a6f-90dd-403c-97d0-94372be1e3e6@gmail.com> In-Reply-To: <0a201a6f-90dd-403c-97d0-94372be1e3e6@gmail.com> From: Marco Elver Date: Thu, 28 Sep 2023 08:02:58 +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: Heiner Kallweit Cc: Mirsad Goran Todorovac , 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (howler.vger.email [0.0.0.0]); Wed, 27 Sep 2023 23:03:58 -0700 (PDT) On Wed, 27 Sept 2023 at 21:52, Heiner Kallweit wrote= : > > 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 [r81= 69] > > > > write (marked) to 0xffff888102474b74 of 4 bytes by task 5358 on cpu 29: > > rtl8169_start_xmit (drivers/net/ethernet/realtek/r8169_main.c:4254) r81= 69 > > dev_hard_start_xmit (./include/linux/netdevice.h:4889 ./include/linux/n= etdevice.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/neigh= bour.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/ipv4/= 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/ne= t/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/smpboot.= 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-rc2-= kcsan-00143-gb5cbe7c00aa0 #41 > > Hardware name: ASRock X670E PG Lightning/X670E PG Lightning, BIOS 1.21 = 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 update= d 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, rtl_t= x_slots_avail(tp), > > 4257 R8169_TX_STOP_T= HRS, > > 4258 R8169_TX_START_= THRS); > > > > The read side is the function rtl_tx(): > > > > 4355 static void rtl_tx(struct net_device *dev, struct rtl8169_priva= te *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_DESC; > > 4365 u32 status; > > 4366 > > 4367 status =3D le32_to_cpu(tp->TxDescArray[entry].o= pts1); > > 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, bytes_c= ompl); > > 4384 WRITE_ONCE(tp->dirty_tx, dirty_tx); > > 4385 > > 4386 netif_subqueue_completed_wake(dev, 0, pkts_comp= l, bytes_compl, > > 4387 rtl_tx_slots_avai= l(tp), > > 4388 R8169_TX_START_TH= RS); > > 4389 /* > > 4390 * 8168 hack: TxPoll requests are lost when the= Tx packets are > > 4391 * too close. Let's kick an extra TxPoll reques= t 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 once = a tx irq is > > 4395 * triggered after the last fragment is marked = 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 w= as 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 read= 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 th= e test in line 4363 > > and line 4397. This test should certainly not be cached by the compiler= in some register > > for such a long time, while asynchronous writes to tp->cur_tx might hav= e occurred in line > > 4254 in the meantime. > > > > netif_subqueue_completed_wake() has barriers ensuring that no cached valu= e for tp->cur_tx > is used in line 4397. I'm not aware of any reported issues with an obviou= s link to the > potentential issue you describe. > I don't have a strong opinion on these patches. They shouldn't hurt, and = 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/too= ls/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 ring= s") > > 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-e9a9-30a6-7c83e6b53188= @alu.unizg.hr/ > > Signed-off-by: Mirsad Goran Todorovac Acked-by: Marco Elver > > --- > > v1: > > the initial patch proposal. fixes the KCSAN warning. > > > > drivers/net/ethernet/realtek/r8169_main.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/et= hernet/realtek/r8169_main.c > > index 6351a2dc13bc..281aaa851847 100644 > > --- a/drivers/net/ethernet/realtek/r8169_main.c > > +++ b/drivers/net/ethernet/realtek/r8169_main.c > > @@ -4394,7 +4394,7 @@ static void rtl_tx(struct net_device *dev, struct= rtl8169_private *tp, > > * If skb is NULL then we come here again once a tx irq i= s > > * triggered after the last fragment is marked transmitte= d. > > */ > > - if (tp->cur_tx !=3D dirty_tx && skb) > > + if (READ_ONCE(tp->cur_tx) !=3D dirty_tx && skb) > > rtl8169_doorbell(tp); > > } > > } >