netdev - [PATCH net] net: let net.core.dev

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Message-ID: <20250116143053.4146855-1-liujian56@huawei.com>
Date: Thu, 16 Jan 2025 22:30:53 +0800
From: Liu Jian <liujian56@...wei.com>
To: <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <horms@...nel.org>, <stephen@...workplumber.org>,
	<matthias.tafelmeier@....net>
CC: <netdev@...r.kernel.org>, <liujian56@...wei.com>
Subject: [PATCH net] net: let net.core.dev_weight always be non-zero

The following problem was encountered during stability test:

(NULL net_device): NAPI poll function process_backlog+0x0/0x530 \
	returned 1, exceeding its budget of 0.
------------[ cut here ]------------
list_add double add: new=ffff88905f746f48, prev=ffff88905f746f48, \
	next=ffff88905f746e40.
WARNING: CPU: 18 PID: 5462 at lib/list_debug.c:35 \
	__list_add_valid_or_report+0xf3/0x130
CPU: 18 UID: 0 PID: 5462 Comm: ping Kdump: loaded Not tainted 6.13.0-rc7+
RIP: 0010:__list_add_valid_or_report+0xf3/0x130
Call Trace:
? __warn+0xcd/0x250
? __list_add_valid_or_report+0xf3/0x130
enqueue_to_backlog+0x923/0x1070
netif_rx_internal+0x92/0x2b0
__netif_rx+0x15/0x170
loopback_xmit+0x2ef/0x450
dev_hard_start_xmit+0x103/0x490
__dev_queue_xmit+0xeac/0x1950
ip_finish_output2+0x6cc/0x1620
ip_output+0x161/0x270
ip_push_pending_frames+0x155/0x1a0
raw_sendmsg+0xe13/0x1550
__sys_sendto+0x3bf/0x4e0
__x64_sys_sendto+0xdc/0x1b0
do_syscall_64+0x5b/0x170
entry_SYSCALL_64_after_hwframe+0x76/0x7e

The reproduction command is as follows:
sysctl -w net.core.dev_weight=0
Ping 127.0.0.1

This is because when the napi's weight is set to 0, process_backlog() may
return 0 and clear the NAPI_STATE_SCHED bit of napi->state, causing this
napi to be re-polled in net_rx_action() until __do_softirq() times out.
Since the NAPI_STATE_SCHED bit has been cleared, napi_schedule_rps() can
be retriggered in enqueue_to_backlog(), causing this issue.

Making the napi's weight always non-zero solves this problem.

Fixes: e38766054509 ("[NET]: Fix sysctl net.core.dev_weight")
Fixes: 3d48b53fb2ae ("net: dev_weight: TX/RX orthogonality")
Signed-off-by: Liu Jian <liujian56@...wei.com>
---
 net/core/sysctl_net_core.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index cb8d32e5c14e..ad2741f1346a 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -319,7 +319,7 @@ static int proc_do_dev_weight(const struct ctl_table *table, int write,
 	int ret, weight;
 
 	mutex_lock(&dev_weight_mutex);
-	ret = proc_dointvec(table, write, buffer, lenp, ppos);
+	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 	if (!ret && write) {
 		weight = READ_ONCE(weight_p);
 		WRITE_ONCE(net_hotdata.dev_rx_weight, weight * dev_weight_rx_bias);
@@ -412,6 +412,7 @@ static struct ctl_table net_core_table[] = {
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= proc_do_dev_weight,
+		.extra1         = SYSCTL_ONE,
 	},
 	{
 		.procname	= "dev_weight_rx_bias",
@@ -419,6 +420,7 @@ static struct ctl_table net_core_table[] = {
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= proc_do_dev_weight,
+		.extra1         = SYSCTL_ONE,
 	},
 	{
 		.procname	= "dev_weight_tx_bias",
@@ -426,6 +428,7 @@ static struct ctl_table net_core_table[] = {
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= proc_do_dev_weight,
+		.extra1         = SYSCTL_ONE,
 	},
 	{
 		.procname	= "netdev_max_backlog",
-- 
2.34.1