netdev - Re: [PATCH net] selftests: rtnetlink: try double sleep to give WQ a chance

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Message-ID: <20250711071729.14d727f6@kernel.org>
Date: Fri, 11 Jul 2025 07:17:29 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Hangbin Liu <liuhangbin@...il.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
 pabeni@...hat.com, andrew+netdev@...n.ch, horms@...nel.org,
 shuah@...nel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net] selftests: rtnetlink: try double sleep to give WQ a
 chance

On Fri, 11 Jul 2025 02:14:03 +0000 Hangbin Liu wrote:
> >  	sleep 5
> > +	# Schedule out for a bit, address GC runs from the power efficient WQ
> > +	# if the long sleep above has put the whole system into sleep state
> > +	# the WQ may have not had a chance to run.
> > +	sleep 0.1
> > +  
> 
> How about use slowwait to check if the address still exists.

Weirdly if we read the addresses twice they disappear, I haven't looked
into the code for the why, but seemed like using slowwait could
potentially mask the addresses sticking around when nobody runs 
the Netlink handlers for a while? Dunno..

I queued this debug patch a couple of months ago:

 	sleep 5
-	run_cmd_grep_fail "10.23.11." ip addr show dev "$devdummy"
+	ip addr show dev "$devdummy" > /tmp/a
+	run_cmd_grep_fail "10.23.11." cat /tmp/a
 	if [ $? -eq 0 ]; then
-		check_err 1
-		end_test "FAIL: preferred_lft addresses remaining"
+	    check_err 1
+	    cat /tmp/a
+	    echo "==="
+		ip addr show dev "$devdummy"
+		end_test "FAIL: preferred_lft addresses remaining ($lft)"
 		return
 	fi

And when it flakes the output looks like this:

# 7.23 [+7.00] 297: test-dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000
# 7.23 [+0.00]     link/ether 9e:a6:c4:c2:1b:16 brd ff:ff:ff:ff:ff:ff
# 7.23 [+0.00]     inet 10.23.11.81/32 scope global deprecated dynamic test-dummy0
# 7.23 [+0.00]        valid_lft 0sec preferred_lft 0sec
# 7.23 [+0.00]     inet 10.23.11.84/32 scope global deprecated dynamic test-dummy0
# 7.24 [+0.00]        valid_lft 0sec preferred_lft 0sec
# 7.24 [+0.00]     inet 10.23.11.93/32 scope global deprecated dynamic test-dummy0
# 7.24 [+0.00]        valid_lft 0sec preferred_lft 0sec
# 7.24 [+0.00]     inet 10.23.11.94/32 scope global deprecated dynamic test-dummy0
# 7.24 [+0.00]        valid_lft 0sec preferred_lft 0sec
# 7.24 [+0.00]     inet 10.23.11.97/32 scope global deprecated dynamic test-dummy0
# 7.24 [+0.00]        valid_lft 0sec preferred_lft 0sec
# 7.24 [+0.00]     inet 10.23.11.99/32 scope global deprecated dynamic test-dummy0
# 7.24 [+0.00]        valid_lft 0sec preferred_lft 0sec
# 7.24 [+0.00]     inet6 fe80::9ca6:c4ff:fec2:1b16/64 scope link proto kernel_ll 
# 7.24 [+0.00]        valid_lft forever preferred_lft forever
# 7.24 [+0.00] ===
# 7.25 [+0.00] 297: test-dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000
# 7.25 [+0.00]     link/ether 9e:a6:c4:c2:1b:16 brd ff:ff:ff:ff:ff:ff
# 7.25 [+0.00]     inet6 fe80::9ca6:c4ff:fec2:1b16/64 scope link proto kernel_ll 
# 7.25 [+0.00]        valid_lft forever preferred_lft forever
# 7.25 [+0.00] FAIL: preferred_lft addresses remaining (1)