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Date: Mon, 18 Sep 2023 11:43:23 +0200
From: Mirsad Todorovac <mirsad.todorovac@....unizg.hr>
To: Eric Dumazet <edumazet@...gle.com>
Cc: nic_swsd@...ltek.com, Heiner Kallweit <hkallweit1@...il.com>,
"David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: BUG: KCSAN: data-race in rtl8169_poll
On 9/18/23 09:41, Eric Dumazet wrote:
> On Mon, Sep 18, 2023 at 8:15 AM Mirsad Todorovac
> <mirsad.todorovac@....unizg.hr> wrote:
>>
>> Hi all,
>>
>> In the vanilla torvalds tree kernel on Ubuntu 22.04, commit 6.6.0-rc1-kcsan-00269-ge789286468a9,
>> KCSAN discovered a data-race in rtl8169_poll():
>>
>> [ 9591.740976] ==================================================================
>> [ 9591.740990] BUG: KCSAN: data-race in rtl8169_poll (drivers/net/ethernet/realtek/r8169_main.c:4430 drivers/net/ethernet/realtek/r8169_main.c:4583) r8169
>>
>> [ 9591.741060] race at unknown origin, with read to 0xffff888109773130 of 4 bytes by interrupt on cpu 21:
>> [ 9591.741073] rtl8169_poll (drivers/net/ethernet/realtek/r8169_main.c:4430 drivers/net/ethernet/realtek/r8169_main.c:4583) r8169
>> [ 9591.741135] __napi_poll (net/core/dev.c:6527)
>> [ 9591.741149] net_rx_action (net/core/dev.c:6596 net/core/dev.c:6727)
>> [ 9591.741161] __do_softirq (kernel/softirq.c:553)
>> [ 9591.741175] __irq_exit_rcu (kernel/softirq.c:427 kernel/softirq.c:632)
>> [ 9591.741185] irq_exit_rcu (kernel/softirq.c:647)
>> [ 9591.741194] common_interrupt (arch/x86/kernel/irq.c:247 (discriminator 14))
>> [ 9591.741206] asm_common_interrupt (./arch/x86/include/asm/idtentry.h:636)
>> [ 9591.741217] cpuidle_enter_state (drivers/cpuidle/cpuidle.c:291)
>> [ 9591.741227] cpuidle_enter (drivers/cpuidle/cpuidle.c:390)
>> [ 9591.741237] call_cpuidle (kernel/sched/idle.c:135)
>> [ 9591.741249] do_idle (kernel/sched/idle.c:219 kernel/sched/idle.c:282)
>> [ 9591.741259] cpu_startup_entry (kernel/sched/idle.c:378 (discriminator 1))
>> [ 9591.741268] start_secondary (arch/x86/kernel/smpboot.c:210 arch/x86/kernel/smpboot.c:294)
>> [ 9591.741281] secondary_startup_64_no_verify (arch/x86/kernel/head_64.S:433)
>>
>> [ 9591.741300] value changed: 0x80003fff -> 0x34044510
>>
>> [ 9591.741314] Reported by Kernel Concurrency Sanitizer on:
>> [ 9591.741322] CPU: 21 PID: 0 Comm: swapper/21 Tainted: G L 6.6.0-rc1-kcsan-00269-ge789286468a9-dirty #4
>> [ 9591.741334] Hardware name: ASRock X670E PG Lightning/X670E PG Lightning, BIOS 1.21 04/26/2023
>> [ 9591.741343] ==================================================================
>>
>> (The taint is not from the proprietary module, but triggered from the previous reported and unfixed bug.)
>>
>> Apparently, it is this code:
>>
>> static int rtl8169_poll(struct napi_struct *napi, int budget)
>> {
>> struct rtl8169_private *tp = container_of(napi, struct rtl8169_private, napi);
>> struct net_device *dev = tp->dev;
>> int work_done;
>>
>> rtl_tx(dev, tp, budget);
>>
>> → work_done = rtl_rx(dev, tp, budget);
>>
>> if (work_done < budget && napi_complete_done(napi, work_done))
>> rtl_irq_enable(tp);
>>
>> return work_done;
>> }
>>
>> and
>>
>> static int rtl_rx(struct net_device *dev, struct rtl8169_private *tp, int budget)
>> {
>> struct device *d = tp_to_dev(tp);
>> int count;
>>
>> for (count = 0; count < budget; count++, tp->cur_rx++) {
>> unsigned int pkt_size, entry = tp->cur_rx % NUM_RX_DESC;
>> struct RxDesc *desc = tp->RxDescArray + entry;
>> struct sk_buff *skb;
>> const void *rx_buf;
>> dma_addr_t addr;
>> u32 status;
>>
>> → status = le32_to_cpu(desc->opts1);
>> if (status & DescOwn)
>> break;
>>
>> /* This barrier is needed to keep us from reading
>> * any other fields out of the Rx descriptor until
>> * we know the status of DescOwn
>> */
>> dma_rmb();
>>
>> if (unlikely(status & RxRES)) {
>> .
>> .
>> .
>>
>> The reason isn't obvious, so it might be interesting if this is a valid report and whether it caused spurious corruption
>> of the network data on Realtek 8169 compatible cards ...
>>
>
> I think this is pretty much expected.
>
> Driver reads a piece of memory that the hardware can modify.
>
> Adding data_race() annotations could avoid these false positives.
>
>> Hope this helps.
>>
>> Best regards,
>> Mirsad Todorovac
Well, another approach was this quick fix that eliminated all those rtl8169_poll() KCSAN warnings.
If READ_ONCE(desc->opts1) fixed it, then maybe there is more to this than meets the eye?
-------------------------------------------------
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 6351a2dc13bc..051551ee2a15 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;
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