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Date: Tue, 10 Jul 2018 19:28:49 -0700
From: "Nambiar, Amritha" <amritha.nambiar@...el.com>
To: Andrei Vagin <avagin@...tuozzo.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net,
alexander.h.duyck@...el.com, willemdebruijn.kernel@...il.com,
sridhar.samudrala@...el.com, alexander.duyck@...il.com,
edumazet@...gle.com, hannes@...essinduktion.org,
tom@...bertland.com, tom@...ntonium.net, jasowang@...hat.com,
gaowanlong@...fujitsu.com
Subject: Re: [net-next, v6, 6/7] net-sysfs: Add interface for Rx queue(s) map
per Tx queue
On 7/4/2018 12:20 AM, Andrei Vagin wrote:
> Hello Amritha,
>
> I see a following warning on 4.18.0-rc3-next-20180703.
> It looks like a problem is in this series.
>
> [ 1.084722] ============================================
> [ 1.084797] WARNING: possible recursive locking detected
> [ 1.084872] 4.18.0-rc3-next-20180703+ #1 Not tainted
> [ 1.084949] --------------------------------------------
> [ 1.085024] swapper/0/1 is trying to acquire lock:
> [ 1.085100] 00000000cf973d46 (cpu_hotplug_lock.rw_sem){++++}, at: static_key_slow_inc+0xe/0x20
> [ 1.085189]
> [ 1.085189] but task is already holding lock:
> [ 1.085271] 00000000cf973d46 (cpu_hotplug_lock.rw_sem){++++}, at: init_vqs+0x513/0x5a0
> [ 1.085357]
> [ 1.085357] other info that might help us debug this:
> [ 1.085450] Possible unsafe locking scenario:
> [ 1.085450]
> [ 1.085531] CPU0
> [ 1.085605] ----
> [ 1.085679] lock(cpu_hotplug_lock.rw_sem);
> [ 1.085753] lock(cpu_hotplug_lock.rw_sem);
> [ 1.085828]
> [ 1.085828] *** DEADLOCK ***
> [ 1.085828]
> [ 1.085916] May be due to missing lock nesting notation
> [ 1.085916]
> [ 1.085998] 3 locks held by swapper/0/1:
> [ 1.086074] #0: 00000000244bc7da (&dev->mutex){....}, at: __driver_attach+0x5a/0x110
> [ 1.086164] #1: 00000000cf973d46 (cpu_hotplug_lock.rw_sem){++++}, at: init_vqs+0x513/0x5a0
> [ 1.086248] #2: 000000005cd8463f (xps_map_mutex){+.+.}, at: __netif_set_xps_queue+0x8d/0xc60
> [ 1.086336]
> [ 1.086336] stack backtrace:
> [ 1.086419] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.0-rc3-next-20180703+ #1
> [ 1.086504] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> [ 1.086587] Call Trace:
> [ 1.086667] dump_stack+0x85/0xcb
> [ 1.086744] __lock_acquire+0x68a/0x1330
> [ 1.086821] ? lock_acquire+0x9f/0x200
> [ 1.086900] ? find_held_lock+0x2d/0x90
> [ 1.086976] ? lock_acquire+0x9f/0x200
> [ 1.087051] lock_acquire+0x9f/0x200
> [ 1.087126] ? static_key_slow_inc+0xe/0x20
> [ 1.087205] cpus_read_lock+0x3e/0x80
> [ 1.087280] ? static_key_slow_inc+0xe/0x20
> [ 1.087355] static_key_slow_inc+0xe/0x20
> [ 1.087435] __netif_set_xps_queue+0x216/0xc60
> [ 1.087512] virtnet_set_affinity+0xf0/0x130
> [ 1.087589] init_vqs+0x51b/0x5a0
> [ 1.087665] virtnet_probe+0x39f/0x870
> [ 1.087742] virtio_dev_probe+0x170/0x220
> [ 1.087819] driver_probe_device+0x30b/0x480
> [ 1.087897] ? set_debug_rodata+0x11/0x11
> [ 1.087972] __driver_attach+0xe0/0x110
> [ 1.088064] ? driver_probe_device+0x480/0x480
> [ 1.088141] bus_for_each_dev+0x79/0xc0
> [ 1.088221] bus_add_driver+0x164/0x260
> [ 1.088302] ? veth_init+0x11/0x11
> [ 1.088379] driver_register+0x5b/0xe0
> [ 1.088402] ? veth_init+0x11/0x11
> [ 1.088402] virtio_net_driver_init+0x6d/0x90
> [ 1.088402] do_one_initcall+0x5d/0x34c
> [ 1.088402] ? set_debug_rodata+0x11/0x11
> [ 1.088402] ? rcu_read_lock_sched_held+0x6b/0x80
> [ 1.088402] kernel_init_freeable+0x1ea/0x27b
> [ 1.088402] ? rest_init+0xd0/0xd0
> [ 1.088402] kernel_init+0xa/0x110
> [ 1.088402] ret_from_fork+0x3a/0x50
> [ 1.094190] i8042: PNP: PS/2 Controller [PNP0303:KBD,PNP0f13:MOU] at 0x60,0x64 irq 1,12
>
>
> https://travis-ci.org/avagin/linux/jobs/399867744
>
With this patch series, I introduced static_key for XPS maps
(xps_needed), so static_key_slow_inc() is used to switch branches. The
definition of static_key_slow_inc() has cpus_read_lock in place. In the
virtio_net driver, XPS queues are initialized after setting the
queue:cpu affinity in virtnet_set_affinity() which is already protected
within cpus_read_lock. Hence, the warning here trying to acquire
cpus_read_lock when it is already held.
A quick fix for this would be to just extract netif_set_xps_queue() out
of the lock by simply wrapping it with another put/get_online_cpus
(unlock right before and hold lock right after). But this may not a
clean solution. It'd help if I can get suggestions on what would be a
clean option to fix this without extensively changing the code in
virtio_net. Is it mandatory to protect the affinitization with
read_lock? I don't see similar lock in other drivers while setting the
affinity. I understand this warning should go away, but isn't it safe to
have multiple readers.
> On Fri, Jun 29, 2018 at 09:27:07PM -0700, Amritha Nambiar wrote:
>> Extend transmit queue sysfs attribute to configure Rx queue(s) map
>> per Tx queue. By default no receive queues are configured for the
>> Tx queue.
>>
>> - /sys/class/net/eth0/queues/tx-*/xps_rxqs
>>
>> Signed-off-by: Amritha Nambiar <amritha.nambiar@...el.com>
>> ---
>> net/core/net-sysfs.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 83 insertions(+)
>>
>> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
>> index b39987c..f25ac5f 100644
>> --- a/net/core/net-sysfs.c
>> +++ b/net/core/net-sysfs.c
>> @@ -1283,6 +1283,88 @@ static ssize_t xps_cpus_store(struct netdev_queue *queue,
>>
>> static struct netdev_queue_attribute xps_cpus_attribute __ro_after_init
>> = __ATTR_RW(xps_cpus);
>> +
>> +static ssize_t xps_rxqs_show(struct netdev_queue *queue, char *buf)
>> +{
>> + struct net_device *dev = queue->dev;
>> + struct xps_dev_maps *dev_maps;
>> + unsigned long *mask, index;
>> + int j, len, num_tc = 1, tc = 0;
>> +
>> + index = get_netdev_queue_index(queue);
>> +
>> + if (dev->num_tc) {
>> + num_tc = dev->num_tc;
>> + tc = netdev_txq_to_tc(dev, index);
>> + if (tc < 0)
>> + return -EINVAL;
>> + }
>> + mask = kcalloc(BITS_TO_LONGS(dev->num_rx_queues), sizeof(long),
>> + GFP_KERNEL);
>> + if (!mask)
>> + return -ENOMEM;
>> +
>> + rcu_read_lock();
>> + dev_maps = rcu_dereference(dev->xps_rxqs_map);
>> + if (!dev_maps)
>> + goto out_no_maps;
>> +
>> + for (j = -1; j = netif_attrmask_next(j, NULL, dev->num_rx_queues),
>> + j < dev->num_rx_queues;) {
>> + int i, tci = j * num_tc + tc;
>> + struct xps_map *map;
>> +
>> + map = rcu_dereference(dev_maps->attr_map[tci]);
>> + if (!map)
>> + continue;
>> +
>> + for (i = map->len; i--;) {
>> + if (map->queues[i] == index) {
>> + set_bit(j, mask);
>> + break;
>> + }
>> + }
>> + }
>> +out_no_maps:
>> + rcu_read_unlock();
>> +
>> + len = bitmap_print_to_pagebuf(false, buf, mask, dev->num_rx_queues);
>> + kfree(mask);
>> +
>> + return len < PAGE_SIZE ? len : -EINVAL;
>> +}
>> +
>> +static ssize_t xps_rxqs_store(struct netdev_queue *queue, const char *buf,
>> + size_t len)
>> +{
>> + struct net_device *dev = queue->dev;
>> + struct net *net = dev_net(dev);
>> + unsigned long *mask, index;
>> + int err;
>> +
>> + if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
>> + return -EPERM;
>> +
>> + mask = kcalloc(BITS_TO_LONGS(dev->num_rx_queues), sizeof(long),
>> + GFP_KERNEL);
>> + if (!mask)
>> + return -ENOMEM;
>> +
>> + index = get_netdev_queue_index(queue);
>> +
>> + err = bitmap_parse(buf, len, mask, dev->num_rx_queues);
>> + if (err) {
>> + kfree(mask);
>> + return err;
>> + }
>> +
>> + err = __netif_set_xps_queue(dev, mask, index, true);
>> + kfree(mask);
>> + return err ? : len;
>> +}
>> +
>> +static struct netdev_queue_attribute xps_rxqs_attribute __ro_after_init
>> + = __ATTR_RW(xps_rxqs);
>> #endif /* CONFIG_XPS */
>>
>> static struct attribute *netdev_queue_default_attrs[] __ro_after_init = {
>> @@ -1290,6 +1372,7 @@ static struct attribute *netdev_queue_default_attrs[] __ro_after_init = {
>> &queue_traffic_class.attr,
>> #ifdef CONFIG_XPS
>> &xps_cpus_attribute.attr,
>> + &xps_rxqs_attribute.attr,
>> &queue_tx_maxrate.attr,
>> #endif
>> NULL
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