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    Subject[PATCH] net: make unregister netdev warning timeout configurable
    From
    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.
    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
    ---
    net/Kconfig | 12 ++++++++++++
    net/core/dev.c | 4 +++-
    2 files changed, 15 insertions(+), 1 deletion(-)

    diff --git a/net/Kconfig b/net/Kconfig
    index 8cea808ad9e8d..ebb9cc00ac81d 100644
    --- a/net/Kconfig
    +++ b/net/Kconfig
    @@ -461,6 +461,18 @@ config ETHTOOL_NETLINK
    netlink. It provides better extensibility and some new features,
    e.g. notification messages.

    +config UNREGISTER_NETDEV_TIMEOUT
    + int "Unregister network device timeout in seconds"
    + default 10
    + range 0 3600
    + help
    + 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.
    +
    endif # if NET

    # Used by archs to tell that they support BPF JIT compiler plus which flavour.
    diff --git a/net/core/dev.c b/net/core/dev.c
    index 0f72ff5d34ba0..ca03ee407133b 100644
    --- a/net/core/dev.c
    +++ b/net/core/dev.c
    @@ -10405,7 +10405,9 @@ static void netdev_wait_allrefs(struct net_device *dev)

    refcnt = netdev_refcnt_read(dev);

    - if (refcnt && time_after(jiffies, warning_time + 10 * HZ)) {
    + if (refcnt &&
    + time_after(jiffies, warning_time +
    + CONFIG_UNREGISTER_NETDEV_TIMEOUT * HZ)) {
    pr_emerg("unregister_netdevice: waiting for %s to become free. Usage count = %d\n",
    dev->name, refcnt);
    warning_time = jiffies;
    base-commit: 5aa3c334a449bab24519c4967f5ac2b3304c8dcf
    --
    2.31.0.291.g576ba9dcdaf-goog

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