netdev - Re: [PATCH net-next v5 2/2] selftests: fib_tests: Add a test case for IPv6 garbage collection

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Date: Wed, 2 Aug 2023 21:09:29 -0700
From: Kui-Feng Lee <sinquersw@...il.com>
To: David Ahern <dsahern@...nel.org>, thinker.li@...il.com,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 netdev@...r.kernel.org, pabeni@...hat.com, martin.lau@...ux.dev,
 kernel-team@...a.com, yhs@...a.com
Cc: kuifeng@...a.com
Subject: Re: [PATCH net-next v5 2/2] selftests: fib_tests: Add a test case for
 IPv6 garbage collection



On 8/2/23 19:06, David Ahern wrote:
> On 8/1/23 6:43 PM, thinker.li@...il.com wrote:
> \> @@ -747,6 +750,97 @@ fib_notify_test()
>>   	cleanup &> /dev/null
>>   }
>>   
>> +fib6_gc_test()
>> +{
>> +	echo
>> +	echo "Fib6 garbage collection test"
>> +
>> +	STRACE=$(which strace)
>> +	if [ -z "$STRACE" ]; then
>> +	    echo "    SKIP: strace not found"
>> +	    ret=$ksft_skip
>> +	    return
>> +	fi
>> +
>> +	EXPIRE=10
>> +
>> +	setup
>> +
>> +	set -e
>> +
>> +	# Check expiration of routes every 3 seconds (GC)
>> +	$NS_EXEC sysctl -wq net.ipv6.route.gc_interval=300
>> +
>> +	$IP link add dummy_10 type dummy
>> +	$IP link set dev dummy_10 up
>> +	$IP -6 address add 2001:10::1/64 dev dummy_10
>> +
>> +	$NS_EXEC sysctl -wq net.ipv6.route.flush=1
>> +
>> +	# Temporary routes
>> +	for i in $(seq 1 1000); do
>> +	    # Expire route after $EXPIRE seconds
>> +	    $IP -6 route add 2001:20::$i \
>> +		via 2001:10::2 dev dummy_10 expires $EXPIRE
>> +	done
>> +	N_EXP=$($IP -6 route list |grep expires|wc -l)
>> +	if [ $N_EXP -ne 1000 ]; then
> 
> race condition here ... that you can install all 1000 routes and then
> run this command before any expire. 10 seconds is normally more than
> enough time, but on a loaded server it might not be. And really it does
> not matter. What matters is that you install routes with an expires and
> they disappear when expected - and I believe the flush below should not
> be needed to validate they have been removed.

Without the flush below, the result will be very unpredictable or need 
to wait longer, at least two gc_interval seconds. We can
shorten gc_interval to 10s, but we need to wait for 20s to make it
certain. It is more predictable with the flush.

About race condition, I will remove the check.  Just like what you said,
it is not necessary.