Commit 5aa3afe1 authored by Dmitry Vyukov's avatar Dmitry Vyukov Committed by David S. Miller
Browse files

net: make unregister netdev warning timeout configurable 



netdev_wait_allrefs() issues a warning if refcount does not drop to 0
after 10 seconds. While 10 second wait generally should not happen
under normal workload in normal environment, it seems to fire falsely
very often during fuzzing and/or in qemu emulation (~10x slower).
At least it's not possible to understand if it's really a false
positive or not. Automated testing generally bumps all timeouts
to very high values to avoid flake failures.
Add net.core.netdev_unregister_timeout_secs sysctl to make
the timeout configurable for automated testing systems.
Lowering the timeout may also be useful for e.g. manual bisection.
The default value matches the current behavior.

Signed-off-by: default avatarDmitry Vyukov <dvyukov@google.com>
Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=211877


Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 4c94fe88

Documentation/admin-guide/sysctl/net.rst

+11 −0
Original line number Diff line number Diff line
@@ -311,6 +311,17 @@ permit to distribute the load on several cpus. 
If set to 1 (default), timestamps are sampled as soon as possible, before

queueing.



netdev_unregister_timeout_secs

------------------------------



Unregister network device timeout in seconds.

This option controls the timeout (in seconds) used to issue a warning while

waiting for a network device refcount to drop to 0 during device

unregistration. A lower value may be useful during bisection to detect

a leaked reference faster. A larger value may be useful to prevent false

warnings on slow/loaded systems.

Default value is 10, minimum 0, maximum 3600.



optmem_max

----------

include/linux/netdevice.h

+1 −0
Original line number Diff line number Diff line
@@ -4661,6 +4661,7 @@ void dev_get_tstats64(struct net_device *dev, struct rtnl_link_stats64 *s); 


extern int		netdev_max_backlog;

extern int		netdev_tstamp_prequeue;

extern int		netdev_unregister_timeout_secs;

extern int		weight_p;

extern int		dev_weight_rx_bias;

extern int		dev_weight_tx_bias;

net/core/dev.c

+5 −1
Original line number Diff line number Diff line
@@ -10322,6 +10322,8 @@ int netdev_refcnt_read(const struct net_device *dev) 
}

EXPORT_SYMBOL(netdev_refcnt_read);



int netdev_unregister_timeout_secs __read_mostly = 10;



#define WAIT_REFS_MIN_MSECS 1

#define WAIT_REFS_MAX_MSECS 250

/**
@@ -10383,7 +10385,9 @@ static void netdev_wait_allrefs(struct net_device *dev) 


		refcnt = netdev_refcnt_read(dev);



		if (refcnt != 1 && time_after(jiffies, warning_time + 10 * HZ)) {

		if (refcnt &&

		    time_after(jiffies, warning_time +

			       netdev_unregister_timeout_secs * HZ)) {

			pr_emerg("unregister_netdevice: waiting for %s to become free. Usage count = %d\n",

				 dev->name, refcnt);

			warning_time = jiffies;

net/core/sysctl_net_core.c

+10 −0
Original line number Diff line number Diff line
@@ -24,6 +24,7 @@ 


static int two = 2;

static int three = 3;

static int int_3600 = 3600;

static int min_sndbuf = SOCK_MIN_SNDBUF;

static int min_rcvbuf = SOCK_MIN_RCVBUF;

static int max_skb_frags = MAX_SKB_FRAGS;
@@ -570,6 +571,15 @@ static struct ctl_table net_core_table[] = { 
		.proc_handler	= proc_dointvec_minmax,

		.extra1		= SYSCTL_ONE,

	},

	{

		.procname	= "netdev_unregister_timeout_secs",

		.data		= &netdev_unregister_timeout_secs,

		.maxlen		= sizeof(unsigned int),

		.mode		= 0644,

		.proc_handler	= proc_dointvec_minmax,

		.extra1		= SYSCTL_ZERO,

		.extra2		= &int_3600,

	},

	{ }

};