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Date:   Mon, 16 Oct 2023 09:35:57 +0200
From:   Marco Elver <elver@...gle.com>
To:     Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>
Cc:     Heiner Kallweit <hkallweit1@...il.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, nic_swsd@...ltek.com,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH v1 3/3] r8169: fix the KCSAN reported data race in rtl_rx
 while reading desc->opts1

On Sat, 14 Oct 2023 at 05:16, Mirsad Goran Todorovac
<mirsad.todorovac@....unizg.hr> wrote:
>
> KCSAN reported the following data-race bug:
>
> ==================================================================
> BUG: KCSAN: data-race in rtl8169_poll (drivers/net/ethernet/realtek/r8169_main.c:4430 drivers/net/ethernet/realtek/r8169_main.c:4583) r8169
>
> race at unknown origin, with read to 0xffff888117e43510 of 4 bytes by interrupt on cpu 21:
> rtl8169_poll (drivers/net/ethernet/realtek/r8169_main.c:4430 drivers/net/ethernet/realtek/r8169_main.c:4583) 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)
> sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1074 (discriminator 14))
> asm_sysvec_apic_timer_interrupt (./arch/x86/include/asm/idtentry.h:645)
> 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: 0x80003fff -> 0x3402805f
>
> 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
> ==================================================================
>
> drivers/net/ethernet/realtek/r8169_main.c:
> ==========================================
>    4429
>  → 4430                 status = le32_to_cpu(desc->opts1);
>    4431                 if (status & DescOwn)
>    4432                         break;
>    4433
>    4434                 /* This barrier is needed to keep us from reading
>    4435                  * any other fields out of the Rx descriptor until
>    4436                  * we know the status of DescOwn
>    4437                  */
>    4438                 dma_rmb();
>    4439
>    4440                 if (unlikely(status & RxRES)) {
>    4441                         if (net_ratelimit())
>    4442                                 netdev_warn(dev, "Rx ERROR. status = %08x\n",
>
> Marco Elver explained that dma_rmb() doesn't prevent the compiler to tear up the access to
> desc->opts1 which can be written to concurrently. READ_ONCE() should prevent that from
> happening:
>
>    4429
>  → 4430                 status = le32_to_cpu(READ_ONCE(desc->opts1));
>    4431                 if (status & DescOwn)
>    4432                         break;
>    4433
>
> As the consequence of this fix, this KCSAN warning was eliminated.
>
> Fixes: 6202806e7c03a ("r8169: drop member opts1_mask from struct rtl8169_private")
> Suggested-by: Marco Elver <elver@...gle.com>
> Cc: Heiner Kallweit <hkallweit1@...il.com>
> Cc: nic_swsd@...ltek.com
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: netdev@...r.kernel.org
> Link: https://lore.kernel.org/lkml/dc7fc8fa-4ea4-e9a9-30a6-7c83e6b53188@alu.unizg.hr/
> Signed-off-by: Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>
>
> Signed-off-by: Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>

Double sign-off? Otherwise,

Acked-by: Marco Elver <elver@...gle.com>

> ---
>  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/ethernet/realtek/r8169_main.c
> index 281aaa851847..81be6085a480 100644
> --- a/drivers/net/ethernet/realtek/r8169_main.c
> +++ b/drivers/net/ethernet/realtek/r8169_main.c
> @@ -4427,7 +4427,7 @@ static int rtl_rx(struct net_device *dev, struct rtl8169_private *tp, int budget
>                 dma_addr_t addr;
>                 u32 status;
>
> -               status = le32_to_cpu(desc->opts1);
> +               status = le32_to_cpu(READ_ONCE(desc->opts1));
>                 if (status & DescOwn)
>                         break;
>
> --
> 2.34.1
>

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