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Date: Wed, 8 Aug 2018 20:07:35 -0700
From: Andrei Vagin <avagin@...nvz.org>
To: "David S. Miller" <davem@...emloft.net>
Cc: netdev@...r.kernel.org, Andrei Vagin <avagin@...il.com>,
"Nambiar, Amritha" <amritha.nambiar@...el.com>,
"Michael S. Tsirkin" <mst@...hat.com>,
Jason Wang <jasowang@...hat.com>
Subject: [PATCH net-next v2] net: allow to call netif_reset_xps_queues() under cpus_read_lock
From: Andrei Vagin <avagin@...il.com>
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. Lockdep prints a warning when we are trying to acquire
cpus_read_lock when it is already held.
This patch adds an ability to call __netif_set_xps_queue under
cpus_read_lock().
============================================
WARNING: possible recursive locking detected
4.18.0-rc3-next-20180703+ #1 Not tainted
--------------------------------------------
swapper/0/1 is trying to acquire lock:
00000000cf973d46 (cpu_hotplug_lock.rw_sem){++++}, at: static_key_slow_inc+0xe/0x20
but task is already holding lock:
00000000cf973d46 (cpu_hotplug_lock.rw_sem){++++}, at: init_vqs+0x513/0x5a0
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(cpu_hotplug_lock.rw_sem);
lock(cpu_hotplug_lock.rw_sem);
*** DEADLOCK ***
May be due to missing lock nesting notation
3 locks held by swapper/0/1:
#0: 00000000244bc7da (&dev->mutex){....}, at: __driver_attach+0x5a/0x110
#1: 00000000cf973d46 (cpu_hotplug_lock.rw_sem){++++}, at: init_vqs+0x513/0x5a0
#2: 000000005cd8463f (xps_map_mutex){+.+.}, at: __netif_set_xps_queue+0x8d/0xc60
v2: move cpus_read_lock() out of __netif_set_xps_queue()
Cc: "Nambiar, Amritha" <amritha.nambiar@...el.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Jason Wang <jasowang@...hat.com>
Fixes: 8af2c06ff4b1 ("net-sysfs: Add interface for Rx queue(s) map per Tx queue")
Signed-off-by: Andrei Vagin <avagin@...il.com>
---
drivers/net/virtio_net.c | 4 +++-
net/core/dev.c | 20 +++++++++++++++-----
net/core/net-sysfs.c | 4 ++++
3 files changed, 22 insertions(+), 6 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 62311dde6e71..39a7f4452587 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1903,9 +1903,11 @@ static void virtnet_set_affinity(struct virtnet_info *vi)
i = 0;
for_each_online_cpu(cpu) {
+ const unsigned long *mask = cpumask_bits(cpumask_of(cpu));
+
virtqueue_set_affinity(vi->rq[i].vq, cpu);
virtqueue_set_affinity(vi->sq[i].vq, cpu);
- netif_set_xps_queue(vi->dev, cpumask_of(cpu), i);
+ __netif_set_xps_queue(vi->dev, mask, i, false);
i++;
}
diff --git a/net/core/dev.c b/net/core/dev.c
index f68122f0ab02..325fc5088370 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2176,6 +2176,7 @@ static void netif_reset_xps_queues(struct net_device *dev, u16 offset,
if (!static_key_false(&xps_needed))
return;
+ cpus_read_lock();
mutex_lock(&xps_map_mutex);
if (static_key_false(&xps_rxqs_needed)) {
@@ -2199,10 +2200,11 @@ static void netif_reset_xps_queues(struct net_device *dev, u16 offset,
out_no_maps:
if (static_key_enabled(&xps_rxqs_needed))
- static_key_slow_dec(&xps_rxqs_needed);
+ static_key_slow_dec_cpuslocked(&xps_rxqs_needed);
- static_key_slow_dec(&xps_needed);
+ static_key_slow_dec_cpuslocked(&xps_needed);
mutex_unlock(&xps_map_mutex);
+ cpus_read_unlock();
}
static void netif_reset_xps_queues_gt(struct net_device *dev, u16 index)
@@ -2250,6 +2252,7 @@ static struct xps_map *expand_xps_map(struct xps_map *map, int attr_index,
return new_map;
}
+/* Must be called under cpus_read_lock */
int __netif_set_xps_queue(struct net_device *dev, const unsigned long *mask,
u16 index, bool is_rxqs_map)
{
@@ -2317,9 +2320,9 @@ int __netif_set_xps_queue(struct net_device *dev, const unsigned long *mask,
if (!new_dev_maps)
goto out_no_new_maps;
- static_key_slow_inc(&xps_needed);
+ static_key_slow_inc_cpuslocked(&xps_needed);
if (is_rxqs_map)
- static_key_slow_inc(&xps_rxqs_needed);
+ static_key_slow_inc_cpuslocked(&xps_rxqs_needed);
for (j = -1; j = netif_attrmask_next(j, possible_mask, nr_ids),
j < nr_ids;) {
@@ -2448,11 +2451,18 @@ int __netif_set_xps_queue(struct net_device *dev, const unsigned long *mask,
kfree(new_dev_maps);
return -ENOMEM;
}
+EXPORT_SYMBOL_GPL(__netif_set_xps_queue);
int netif_set_xps_queue(struct net_device *dev, const struct cpumask *mask,
u16 index)
{
- return __netif_set_xps_queue(dev, cpumask_bits(mask), index, false);
+ int ret;
+
+ cpus_read_lock();
+ ret = __netif_set_xps_queue(dev, cpumask_bits(mask), index, false);
+ cpus_read_unlock();
+
+ return ret;
}
EXPORT_SYMBOL(netif_set_xps_queue);
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 0a95bcf64cdc..bd67c4d0fcfd 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -26,6 +26,7 @@
#include <linux/pm_runtime.h>
#include <linux/of.h>
#include <linux/of_net.h>
+#include <linux/cpu.h>
#include "net-sysfs.h"
@@ -1400,7 +1401,10 @@ static ssize_t xps_rxqs_store(struct netdev_queue *queue, const char *buf,
return err;
}
+ cpus_read_lock();
err = __netif_set_xps_queue(dev, mask, index, true);
+ cpus_read_unlock();
+
kfree(mask);
return err ? : len;
}
--
2.17.1
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