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Message-Id: <20230927184158.243575-1-mirsad.todorovac@alu.unizg.hr>
Date: Wed, 27 Sep 2023 20:41:57 +0200
From: Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>
To: Heiner Kallweit <hkallweit1@...il.com>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: 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>,
Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>,
Marco Elver <elver@...gle.com>
Subject: [PATCH RFC v1 1/3] r8169: fix the KCSAN reported data-race in rtl_tx() while reading tp->cur_tx
KCSAN reported the following data-race:
==================================================================
BUG: KCSAN: data-race in rtl8169_poll [r8169] / rtl8169_start_xmit [r8169]
write (marked) to 0xffff888102474b74 of 4 bytes by task 5358 on cpu 29:
rtl8169_start_xmit (drivers/net/ethernet/realtek/r8169_main.c:4254) r8169
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/neighbour.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/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/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
==================================================================
The write side of drivers/net/ethernet/realtek/r8169_main.c is:
==================
4251 /* rtl_tx needs to see descriptor changes before updated tp->cur_tx */
4252 smp_wmb();
4253
→ 4254 WRITE_ONCE(tp->cur_tx, tp->cur_tx + frags + 1);
4255
4256 stop_queue = !netif_subqueue_maybe_stop(dev, 0, rtl_tx_slots_avail(tp),
4257 R8169_TX_STOP_THRS,
4258 R8169_TX_START_THRS);
The read side is the function rtl_tx():
4355 static void rtl_tx(struct net_device *dev, struct rtl8169_private *tp,
4356 int budget)
4357 {
4358 unsigned int dirty_tx, bytes_compl = 0, pkts_compl = 0;
4359 struct sk_buff *skb;
4360
4361 dirty_tx = tp->dirty_tx;
4362
4363 while (READ_ONCE(tp->cur_tx) != dirty_tx) {
4364 unsigned int entry = dirty_tx % NUM_TX_DESC;
4365 u32 status;
4366
4367 status = le32_to_cpu(tp->TxDescArray[entry].opts1);
4368 if (status & DescOwn)
4369 break;
4370
4371 skb = tp->tx_skb[entry].skb;
4372 rtl8169_unmap_tx_skb(tp, entry);
4373
4374 if (skb) {
4375 pkts_compl++;
4376 bytes_compl += skb->len;
4377 napi_consume_skb(skb, budget);
4378 }
4379 dirty_tx++;
4380 }
4381
4382 if (tp->dirty_tx != dirty_tx) {
4383 dev_sw_netstats_tx_add(dev, pkts_compl, bytes_compl);
4384 WRITE_ONCE(tp->dirty_tx, dirty_tx);
4385
4386 netif_subqueue_completed_wake(dev, 0, pkts_compl, bytes_compl,
4387 rtl_tx_slots_avail(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 request 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 */
→ 4397 if (tp->cur_tx != 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) != dirty_tx) {
but the same solution is required for protecting the other access to tp->cur_tx:
→ 4397 if (READ_ONCE(tp->cur_tx) != 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 the 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 have occurred in line
4254 in the meantime.
Fixes: 94d8a98e6235c ("r8169: reduce number of workaround doorbell rings")
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: Marco Elver <elver@...gle.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>
---
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/ethernet/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 is
* triggered after the last fragment is marked transmitted.
*/
- if (tp->cur_tx != dirty_tx && skb)
+ if (READ_ONCE(tp->cur_tx) != dirty_tx && skb)
rtl8169_doorbell(tp);
}
}
--
2.34.1
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