[ovs-dev] [PATCH] dpif-netdev: Fix time delta overflow in case of race for meter lock.

Ilya Maximets i.maximets at ovn.org
Mon Oct 28 17:04:01 UTC 2019

On 25.10.2019 17:55, William Tu wrote:
> On Fri, Oct 25, 2019 at 4:44 AM Ilya Maximets <i.maximets at ovn.org> wrote:
>> There is a race window between getting the time and getting the meter
>> lock.  This could lead to situation where the thread with larger
>> current time (this thread called time_{um}sec() later than others)
>> will acquire meter lock first and update meter->used to the large
>> value.  Next threads will try to calculate time delta by subtracting
>> the large meter->used from their lower time getting the negative value
>> which will be converted to a big unsigned delta.
>> Fix that by assuming that all these threads received packets in the
>> same time in this case, i.e. dropping negative delta to 0.
>> CC: Jarno Rajahalme <jarno at ovn.org>
>> Fixes: 4b27db644a8c ("dpif-netdev: Simple DROP meter implementation.")
>> Reported-at: https://mail.openvswitch.org/pipermail/ovs-dev/2019-September/363126.html
>> Signed-off-by: Ilya Maximets <i.maximets at ovn.org>
>> ---
> Thanks for the fix
> Acked-by: William Tu <u9012063 at gmail.com>

Thanks, William! Applied to master and backported.

Best regards, Ilya Maximets.

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