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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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6
net/core/dev.c
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@@ -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;