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net: make unregister netdev warning timeout configurable

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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: Dmitry 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: David S. Miller <davem@davemloft.net>
This commit is contained in:
Dmitry Vyukov 2021-03-23 07:49:23 +01:00 • committed by David S. Miller
parent 4c94fe88cd
commit 5aa3afe107
4 changed files with 27 additions and 1 deletions
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11
Documentation/admin-guide/sysctl/net.rst
View file

@ -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 If set to 1 (default), timestamps are sampled as soon as possible, before
queueing. 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 optmem_max
---------- ----------

1
include/linux/netdevice.h
View file

@ -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_max_backlog;
extern int netdev_tstamp_prequeue; extern int netdev_tstamp_prequeue;
extern int netdev_unregister_timeout_secs;
extern int weight_p; extern int weight_p;
extern int dev_weight_rx_bias; extern int dev_weight_rx_bias;
extern int dev_weight_tx_bias; extern int dev_weight_tx_bias;

6
net/core/dev.c
View file

@ -10322,6 +10322,8 @@ int netdev_refcnt_read(const struct net_device *dev)
} }
EXPORT_SYMBOL(netdev_refcnt_read); EXPORT_SYMBOL(netdev_refcnt_read);
int netdev_unregister_timeout_secs __read_mostly = 10;
#define WAIT_REFS_MIN_MSECS 1 #define WAIT_REFS_MIN_MSECS 1
#define WAIT_REFS_MAX_MSECS 250 #define WAIT_REFS_MAX_MSECS 250
/** /**
@ -10383,7 +10385,9 @@ static void netdev_wait_allrefs(struct net_device *dev)
refcnt = netdev_refcnt_read(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", pr_emerg("unregister_netdevice: waiting for %s to become free. Usage count = %d\n",
dev->name, refcnt); dev->name, refcnt);
warning_time = jiffies; warning_time = jiffies;

10
net/core/sysctl_net_core.c
View file

@ -24,6 +24,7 @@
static int two = 2; static int two = 2;
static int three = 3; static int three = 3;
static int int_3600 = 3600;
static int min_sndbuf = SOCK_MIN_SNDBUF; static int min_sndbuf = SOCK_MIN_SNDBUF;
static int min_rcvbuf = SOCK_MIN_RCVBUF; static int min_rcvbuf = SOCK_MIN_RCVBUF;
static int max_skb_frags = MAX_SKB_FRAGS; static int max_skb_frags = MAX_SKB_FRAGS;
@ -570,6 +571,15 @@ static struct ctl_table net_core_table[] = {
.proc_handler = proc_dointvec_minmax, .proc_handler = proc_dointvec_minmax,
.extra1 = SYSCTL_ONE, .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,
},
{ } { }
}; };